Core Python Programming (2nd Edition)

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DatabaseError Database error DataError Problems with the processed data OperationalError Error during database operation execution IntegrityError Database relational integrity error InternalError Error that occurs within the database ProgrammingError SQL command failed NotSupportedError Unsupported operation occurred 21.2.2. Connection Objects Connections are how your application gets to talk to the database. They represent the fundamental communication mechanism by which commands are sent to the server and results returned. Once a connection has been established (or a pool of connections), you create cursors to send requests to and receive replies from the database. Methods Connection objects are not required to have any data attributes but should define the methods shown in Table 21.5. Table 21.5. Connection Object Methods Method Name Description close() Close database connection commit() Commit current transaction rollback() Cancel current transaction cursor() Create (and return) a cursor or cursor-like object using this connection errorhandler(cxn, cur, errcls, errval) Serves as a handler for given connection cursor When close() is used, the same connection cannot be used again without running into an exception.
The commit() method is irrelevant if the database does not support transactions or if it has an autocommit feature that has been enabled. You can implement separate methods to turn auto-commit off or on if you wish. Since this method is required as part of the API, databases that do not have the concept of transactions should just implement "pass" for this method. Like commit(), rollback() only makes sense if transactions are supported in the database. After execution, rollback() should leave the database in the same state as it was when the transaction began. According to PEP 249, "Closing a connection without committing the changes first will cause an implicit rollback to be performed." If the RDBMS does not support cursors, cursor() should still return an object that faithfully emulates or imitates a real cursor object. These are just the minimum requirements. Each individual adapter developer can always add special attributes specifically for their interface or database. It is also recommended but not required for adapter writers to make all database module exceptions (see above) available via a connection. If not, then it is assumed that Connection objects will throw the corresponding module-level exception. Once you have completed using your connection and cursors closed, you should commit() any operations and close() your connection. 21.2.3. Cursor Objects Once you have a connection, you can start talking to the database. As we mentioned above in the introductory section, a cursor lets a user issue database commands and retrieve rows resulting from queries. A Python DB-API cursor object functions as a cursor for you, even if cursors are not supported in the database. In this case, the database adapter creator must implement CURSOR objects so that they act like cursors. This keeps your Python code consistent when you switch between database systems that have or do not have cursor support. Once you have created a cursor, you can execute a query or command (or multiple queries and commands) and retrieve one or more rows from the results set. Table 21.6 shows data attributes and methods that cursor objects have. Table 21.6. Cursor Object Attributes Object Attribute Description arraysize Number of rows to fetch at a time with fetch many(); defaults to 1 connection Connection that created this cursor (optional) description Returns cursor activity (7-item tuples): (name, type_code, display_size, internal_ size, precision, scale, null_ok); only name and type_code are required lastrowid Row ID of last modified row (optional; if row IDs not supported, default to None) rowcount Number of rows that the last execute*() produced or affected
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Table of Contents | Index Core Pyth
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The Complete Developer's Guide to P
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Table of Contents | Index Copyright
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Section 6.2. Strings Section 6.3. S
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Section 11.5. Formal Arguments Sect
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Section 19.4. Brief Tour of Other G
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Copyright Many of the designations
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Praise for Core Python Programming
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Prentice Hall Core Series Core J2EE
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Another set of first edition reader
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We will continue to update the book
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Dictionaries are Python's mapping o
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and you will find it fun! We first
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Acknowledgments Acknowledgments for
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Christian Tismer (creator of Stackl
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Chapter 1. Welcome to Python! Chapt
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1.2. Origins Work on Python began i
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which you can build an application,
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often provides an extended distract
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Build It Yourself For most other pl
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Windows/DOS To add Python to your s
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It is also possible in Unix to auto
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MacOS X is very Unix-like (based on
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Figure 1-5. Starting IDLE in Window
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1.6. Python Documentation Python do
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orrow features from languages such
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1.8. Other Implementations The "sta
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1.9. Exercises 1-1. Python Installa
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abs(4) 4 >>> abs(-4) 4 We will intr
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%s means to substitute a string whi
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It's very tempting for beginners to
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2.4. Operators The standard mathema
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2.5. Variables and Assignment Rules
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All numeric types are covered in Ch
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2.8. Lists and Tuples Lists and tup
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2.10. Code Blocks Use Indentation C
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2.12. while Loop The standard while
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Using the string format operator al
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2.14. List Comprehensions These are
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case you would have to revert back
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2.17. Functions Like many other lan
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2.18. Classes Classes are a core pa
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2.19. Modules A module is a logical
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2.20. Useful Functions In this chap
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2-4. User Input with raw_input(). a
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put in your own as you write your c
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Chapter 3. Python Basics Chapter To
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3.1.3. Multiple Statement Groups as
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3.2. Variable Assignment This secti
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Another way of assigning multiple v
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[a] access keyword obsoleted as of
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three PEPs: 7 (Style Guide for C Co
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3. Module imports Import all the mo
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Tests in the main body are an easy
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As responsible programmers, we are
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● It is explicitly removed from a
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Lines 13 The Unix startup line is f
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1 #!/usr/bin/env python 2 3 'readTe
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3.7. Related Modules/Developer Tool
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3-10. Exceptions. Replace the call
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4.1. Python Objects Python uses the
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4.3. Other Built-in Types ● Type
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4.4. Internal Types ● Code ● Fr
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4.5. Standard Type Operators 4.5.1.
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Example 2: foo1 and foo2 reference
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4.5.3. Boolean In the above example
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4.6. Standard Type Built-in Functio
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str(2e10) '20000000000.0' >>> >>> s
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>>> type(foo) # assumes foo instant
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then we do not even need to check b
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4.7. Type Factory Functions Since P
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Another way of categorizing the sta
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Sequence types are those whose elem
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4.10. Exercises 4-1. Python Objects
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Chapter 5. Numbers Chapter Topics
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Okay, now that you have a good idea
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Core Style: Use uppercase "L" with
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5.3. Double Precision Floating Poin
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aComplex.real -8.333 >>> aComplex.i
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Automatic numeric coercion makes li
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True Division This is where divisio
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see that the unary operator binds m
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Bitwise Operator Function ~num (una
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In addition, because of the unifica
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divmod(10,2.5) (4.0, 0.0) >>> divmo
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floor(-1.2) -2.0 round(-1.2) -1.0 -
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5.7. Other Numeric Types 5.7.1. Boo
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cannot "be continued." If we were t
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uniform() Does almost the same thin
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5.9. Exercises The exercises in thi
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Why do we get 134L and not 1342 in
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Chapter 6. Sequences: Strings, List
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obj not in seq Tests if obj is not
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if not provided, or if None is used
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Extended Slicing with Stride Indice
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above. 6.1.3. Built-in Functions (B
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[a] New in Python 2.3. [b] key argu
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considered a substring. To access s
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6.3. Strings and Operators 6.3.1. S
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Notice how the omission of both ind
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numeric identifier strings that we
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method (see example below). There i
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6.4. String-Only Operators 6.4.1. F
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'6c' >>> >>> "%X" % 108 '6C' >>> >>
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>>> print s.substitute(lang='Python
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6.5. Built-in Functions 6.5.1. Stan
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isinstance() calls to verify type:
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string.isalpha() [a] , [b] [c] Retu
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>>> quest.endswith('color?') True >
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\t 011 9 0x09 HT Horizontal tab \n
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string was created when the operati
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convert the numeric value of the by
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Example 6.2. Simple Unicode String
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Mistake #2: Using the string module
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6.9. Related Modules Table 6.10 lis
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6.10. Summary of String Highlights
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How to Update Lists You can update
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str_list[2] 'over' >>> str_list[:2]
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Traceback (innermost last): File ""
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3. 4. 5. If elements are of the sam
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sum(a, 5) 20 >>> a = [6., 4., 5.] >
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[a] Removes and returns obj at give
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original list object is left as is,
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28 while True: 29 while True: 30 tr
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(Q)uit Enter choice: v You picked:
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Line-by-Line Explanation Because of
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6.16. Tuples Tuples are another con
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6.17. Tuple Operators and Built-in
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6.18. Special Features of Tuples 6.
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(4, True, 5) >>> (4, 2) < (3, 5) #
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6.19. Related Modules Table 6.12 li
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[id(x) for x in hubby] [9919616, 11
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6.21. Summary of Sequences Sequence
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str() • • • strip() • swapc
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d. Take a string and append a backw
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6-12. Strings. a. b. c. Create a fu
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6-19. Multi-Column Output. Given an
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7.1. Mapping Type: Dictionaries Dic
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dict2 = {'name': 'earth', 'port': 8
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dict2['arch'] = 'sunos5' # add new
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Beginning with Python 2.2, programm
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size, their keys match, and so do t
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dict(zip(('x', 'y'), (1, 2))) {'y':
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7.4. Mapping Type Built-in Methods
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dict2= {'host':'earth', 'port':80}
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7.5. Dictionary Keys Dictionary val
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39 try: 40 choice = raw_input(promp
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7.6. Set Types In mathematics, a se
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... print i ... c e h o p s How to
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superset of the second set (is a su
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s &= set('shop') >>> s set(['h', 's
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7.9. Set Type Built-in Methods 7.9.
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7.10. Operator, Function/Method Sum
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7.11. Related Modules The sets modu
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7-5. userpw2.py. The following prob
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characters in srcstr that are beyon
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Chapter 8. Conditionals and Loops C
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8.2. else Statement Like other lang
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8.3. elif (aka else-if) Statement e
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8.4. Conditional Expressions (aka "
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One must use caution when using whi
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Iterating by Sequence Item >>> name
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ange(start, end, step=1) range() wi
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are "sequence-related" is that half
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8.8. continue Statement Core Note:
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8.10. else Statement ... Take Two I
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8.11. Iterators and the iter() Func
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Dictionaries Dictionaries and files
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8.12. List Comprehensions List comp
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and split each line up into words,
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of building up this long list, it w
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lines)? That way, we can use the ma
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8.15. Exercises 8-1. Conditionals.
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8-9. Fibonacci Numbers. The Fibonac
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Chapter 9. Files and Input/Output C
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9.2. File Built-in Functions [open(
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you see references to open(), you c
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Note that there is no "writeline()"
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We originally described how this pr
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f.seek(-12, 1) # move back 12 bytes
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9.4. File Built-in Attributes File
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9.6. Command-Line Arguments The sys
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9.7. File System Access to your fil
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Separation basename() Remove direct
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53 print '*** deleting test file' 5
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to confirm that the directory is in
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9.8. File Execution Whether we want
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other external extension modules th
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9.10. Related Modules There are ple
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Some other Python modules that gene
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9-10. Home Finances. Create a home
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9-15. Copying Files. Prompt for two
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9-24. File Transfer Between Archive
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10.1. What Are Exceptions? 10.1.1.
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10.2. Exceptions in Python As you w
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our case with the foo (non-)attribu
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As you can see, our code now runs s
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etval = None return retval Bear in
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except (Exc1[, Exc2[, ... ExcN]])[,
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except Exception, e: # handle real
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try: ... float(['float() does not',
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13 log = open('cardlog.txt', 'w') 1
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determine whether there were defect
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log.write('no txns this month\n') f
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10.4. Context Management 10.4.1. wi
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Now the with_suite executes. When e
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10.6. Raising Exceptions The interp
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aise string, args, tb Same as above
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try: assert 1 == 0, 'One does not e
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[d] Error in FloatingPointError flo
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[h] Unicode- UnicodeError related e
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10.9. *Creating Exceptions Although
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79 f.close() 80 81 for eachTest in
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the host's name and the port number
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10.10. Why Exceptions (Now)? There
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10.12. Exceptions and the sys Modul
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10.14. Exercises 10-1. Raising Exce
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10-9. Improving math.sqrt(). The ma
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11.1. What Are Functions? Functions
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Stated Number of Objects to Return
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Keyword arguments may also be used
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Line-by-Line Explanation Lines 14 O
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11.3. Creating Functions 11.3.1. de
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modules foo and bar, but can use th
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The main motivation behind decorato
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func = deco1(deco_arg)(deco2(func))
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11.4. Passing Functions The concept
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11.5. Formal Arguments A Python fun
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mandatory, whereas default argument
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11.6. Variable-Length Arguments The
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formal arg1: 1220 formal arg2: 740.
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We will leave a timeit() function a
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11.7. Functional Programming Python
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a(0,9) 9 >>> >>> b = lambda *z: z >
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In Figure 11-1, we observe our orig
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consisting of all the return values
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sequences together. This idiom was
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print 'the total is:', reduce((lamb
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some of those arguments, such as ma
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11.8. Variable Scope The scope of a
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print is_this_global def 11.8.3. Nu
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count2 = counter(100) >>> print cou
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For example, let us assume that fun
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name, e.g., post_logged() will log
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variable. Beginning in 2.1, the ent
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11.9. *Recursion A function is recu
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Now that we have our generator func
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count.next() 5 >>> count.next() 6 >
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11-3. Functions. In this exercise,
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11-14. *Recursion. We also looked a
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12.1. What Are Modules? A module al
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definitely vary as you go from syst
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Notice that each of the namespaces
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You will see just how useful they a
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It is possible to import specific m
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12.5. Features of Module Import 12.
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# impter.py # ############# import
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getting them "registered" (or rathe
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foo() We are going to ask for the d
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Furthermore, we can go down one mor
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12.8. Other Features of Modules 12.
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# overly massive handlers for the c
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12.9. Related Modules The following
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12-6. Extended Import. Create a new
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13.1. Introduction Before we get in
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class MyNewObjectType: 'define MyNe
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(We will add print statements to ou
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Each subclass must define its own c
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13.2. Object-Oriented Programming T
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interfacing with components of the
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derive; and class_suite consists of
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100 >>> C.foo = C.foo + 1 >>> print
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As you can tell, dir() returns a li
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ascertain the location of a class s
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In contrast for those of you using
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id(c1), id(c2), id(c3) # all refer
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13.6. Instance Attributes Instances
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wasWkEnd = HotelRoomCalc(119, 0.045
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The __dict__ attribute consists of
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However, we can only update the val
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As we have seen above, it is perilo
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override a parent method where you
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tcm = TestClassMethod() >>> TestCla
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13.10. Subclassing and Derivation C
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13.11. Inheritance Inheritance desc
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Now let us create the child class C
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class C(P): def __init__(self): sup
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def keys(self): return sorted(self.
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gc = GC() >>> gc.foo() # GC C1 P1 c
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class B(object): pass class C(objec
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isinstance(c2, C2) True >>> isinsta
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The super() function was added in 2
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13.13. Customizing Classes with Spe
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C.__*rshift__(self, obj) Right shif
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The Numeric Types set of special me
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We still have a few problems ... on
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The output is very nice, exactly wh
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1 #!/usr/bin/env python 2 3 class T
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from randseq import RandSeq >>> for
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Addition We define the addition ope
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[9 :: 'foofoofoo'] >>> b + e [3 ::
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which we raise in such cases. Lines
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13.15. *Delegation 13.15.1. Wrappin
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wrappedComplex.imag # imaginary att
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Creation time, modification time, a
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Wrapping a Specific Object with Enh
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13.16. Advanced Features of New-Sty
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preventing users from adding instan
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A descriptor is a class attribute,
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hide such a descriptor, just as you
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43 FileDescr.saved.remove(self.name
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If we try it out, we see that it sa
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def fget(self): return ~self.__x de
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print '*** Created class %r at: %s'
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44 __metaclass__ = ReqStrSugRepr 45
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... print '%s(%d, %d) = %d' % \ ...
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13.18. Exercises 13-1. Programming.
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cash.update(100000.4567) >>> cash 1
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13-9. Queue Class. A queue is a dat
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13-17. Subclassing Numeric Types. T
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Chapter 14. Execution Environment C
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Internally, BIFs are represented as
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__dict__ object. Later on in this c
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>>> c.foo # bound method object >>
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14.2. Code Objects Callables are a
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14.3.2. compile() compile() is a fu
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not a string representation of an i
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The above was performed with raw_in
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-----------------------------------
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A sequence was chosen; enter the se
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them into real Python objects. Othe
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import import2 And here are the con
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$ python /usr/local/lib/python2x/CG
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wait() Wait for child process to co
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As you can see, popen() returns a f
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14.5.5. subprocess Module After Pyt
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14.6. Restricted Execution At one t
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Calling sys.exit() causes the Pytho
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14.8. Miscellaneous Operating Syste
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14.9. Related Modules In Table 14.9
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14-9. Shells. Create a shell (opera
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Chapter 15. Regular Expressions Cha
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Python supports REs through the sta
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15.2. Special Symbols and Character
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"\.". 15.2.3. Matching from the Beg
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We will now introduce the most comm
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\d+(\.\d*)? Strings representing si
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match(pattern, string, flags=0) Att
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m = re.match('foo', 'foo') # patter
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15.3.7. Matching Any Single Charact
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... >>> In the above code, we creat
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Subgroup searches result in a more
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saving the output to a whodata.txt
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15.4. Regular Expressions Example W
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domain. After the final double-colo
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patt = '\d+-\d+-\d+' >>> re.search(
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15.5. Exercises Regular Expressions
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15-19. Extract the complete timesta
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16.1. Introduction 16.1.1. What Is
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The teller is, of course, the serve
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16.2. Sockets: Communication Endpoi
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word "datagram." Because these sock
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Method Description Server Socket Me
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We do not implement this in our exa
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it can immediately make a connectio
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One way to create this "friendly" e
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cs = socket() # create client socke
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[a] Socket address families support
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16.4. *SocketServer Module SocketSe
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Lines 1115 18 print 'waiting for co
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$ And here is the server's: $ tsTse
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This is a timestamp TCP server usin
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calling the write() method of the t
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16.7. Exercises 16-1. Sockets. What
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3. Add logging capability to your n
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17.1. What Are Internet Clients? Be
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3. 4. Client logs in with username
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pwd() Current working directory cwd
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31 f.quit() 32 return 33 print '***
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after-hours, using Python is a grea
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17.3.3. Python and NNTP Based on yo
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article (id) Also similar to body()
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16 except socket.gaierror, e: 17 pr
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deltas = [ x[1]-x[0] for x in parti
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17.4. Electronic Mail Electronic ma
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4. Make service request(s) Quit As
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data: (250, 'ok ; id=20051226235837
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... p.quit() Before we take a look
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any errors. Example 17.3. SMTP and
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17.5. Related Modules One of Python
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17.6. Exercises FTP 17-1. Simple FT
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E-MAIL 17-16. Threaded Newsreader.
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Miscellaneous c. d. e. - Is the mes
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Chapter 18. Multithreaded Programmi
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18.2. Threads and Processes 18.2.1.
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Those of you interested in the sour
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18.3.5. Python Threading Modules Py
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The same loops from onethr.py are e
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25 thread.start_new_thread(loop, 26
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18.5. tHReading Module We will now
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isDaemon() Return daemon flag of th
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In this example we pass in a callab
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19 print 'start loop', nloop, 'at:'
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16 def sum(x): 17 sleep(0.1) 18 if
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We use the Queue module to provide
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for random numbers!) Seriously, tho
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18.7. Exercises 18-1. Processes ver
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Chapter 19. GUI Programming Chapter
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distribution for specific instructi
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some applications use root rather t
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either from the Tkinter topics page
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Example 19.2. Button Widget Demo (t
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in the Label widget. The greater th
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PFAs fits perfectly into a situatio
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Lines 3033 These lines represent ou
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71 def doLS(self, ev=None): 72 erro
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Line-by-Line Explanation Lines 15 T
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The last pieces of code in listdir.
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Things are different once we start
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Our second example uses the Python
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Lines 537 Here we instantiate a Fra
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our primary widgets. This is exactl
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Qt/KDE-Related Modules PyQt Python
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19-9. Multithreaded Chat Applicatio
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20.1. Introduction This introductor
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As you can see from the figure, the
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net_loc can be broken down into sev
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urlunparse(urltup) Unparses a tuple
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urlretrieve(urlstr, localfile=None,
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87 if eachLink not in self.q: 88 se
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urllib Functions Description urlope
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(). This code was inspired by Mike
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parse the newly downloaded page and
Page 882 and 883: 20.4. CGI: Helping Web Servers Proc
Page 884 and 885: Finally, as you can probably guess,
Page 886 and 887: This HTML file presents a form to t
Page 888 and 889: Example 20.4. Results Screen CGI co
Page 890 and 891: Both friends.html and friends1.py a
Page 892 and 893: The other reason for creating actio
Page 894 and 895: 12 ERROR 13 %s 14 16 ''' 17 18 def
Page 896 and 897: link with all the existing informat
Page 898 and 899: Now the user is able to make change
Page 900 and 901: This script outputs Unicode strings
Page 902 and 903: When more than one checkbox is subm
Page 904 and 905: Figure 20-16. Submitting our advanc
Page 906 and 907: Figure 20-17. Results page generate
Page 908 and 909: This script has one main class that
Page 910 and 911: 113 MAXBYTES = 1024 114 langlist =
Page 912 and 913: all the information and sends the f
Page 914 and 915: 20.8. Web (HTTP) Servers Until now,
Page 916 and 917: 33 main() This server subclasses Ba
Page 918 and 919: [b] Interface to the non-validating
Page 920 and 921: 20.10. Exercises 20-1. urllib Modul
Page 922 and 923: 20-19. Electronic Commerce Engine.
Page 924 and 925: Chapter 21. Database Programming Ch
Page 926 and 927: When you query a database, you can
Page 928 and 929: Python world. As a software enginee
Page 930 and 931: This string (not float) indicates t
Page 934 and 935: callproc( func[, args]) Call a stor
Page 936 and 937: ● http://python.org/topics/databa
Page 938 and 939: cur.execute("INSERT INTO users VALU
Page 940 and 941: '', None, '{pgsql=C*T*/pgsql}'] ['t
Page 942 and 943: 23 24 if db == 'sqlite': 25 try: 26
Page 944 and 945: 140 db = setup() 141 print '*** Con
Page 946 and 947: whereas Gadfly does not, so rows ha
Page 948 and 949: 21.3. Object-Relational Managers (O
Page 950 and 951: 54 def insert(self): 55 d = [dict(z
Page 952 and 953: 44 def create(self): 45 Users = sel
Page 954 and 955: the rows from the database and pret
Page 956 and 957: The code works something like this:
Page 958 and 959: We hope that we have provided you w
Page 960 and 961: adodbapi http://adodbapi.sf.net Syb
Page 962 and 963: Chapter 22. Extending Python Chapte
Page 964 and 965: ● Added/extra (non-Python) functi
Page 966 and 967: The following code represents our l
Page 968 and 969: usr/include/python2.x, where the "2
Page 970 and 971: } res = PyArg_ParseTuple(args, "i",
Page 972 and 973: PyArg_ParseTupleAndKeywords() with
Page 974 and 975: $ python setup.py build running bui
Page 976 and 977: 1 #include 2 #include 3 #include
Page 978 and 979: after its reference count has decre
Page 980 and 981: 22.3. Related Topics SWIG There is
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22.4. Exercises 22-1. Extending Pyt
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23.1. Web Services There are many W
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The field names are given in the or
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23.2. Programming Microsoft Office
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This script launches Excel and writ
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23.2.3. Microsoft Word The next dem
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Applying PowerPoint in an applicati
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This script launches Outlook, creat
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Then when you are trying to send a
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Lines 113 We import all of the attr
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23.3. Python and Java Programming w
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Example 23.8. Swing "Hello World" i
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23.4. Exercises Web Services 23-1.
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23-15. Excel Cell Formatting. In th
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23-21. Python and Jython. Find a Py
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Chapter 22 Chapter 23
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or print i, s[i] for i, x in enumer
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Chapter 4 1. Python objects All Pyt
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When i % 2 == 0, it's even (divisib
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Chapter 7 1. Dictionary methods dic
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Chapter 8 3. range() built-in funct
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Chapter 10 1. Raising exceptions e)
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Chapter 12 2. Importing attributes
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Chapter 14 1. Callable objects Func
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9. Python floats [0-9]+(\.[0-9]*)?
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Chapter 17 20. Identifiers pass is
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Chapter 19 1. Client/server archite
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Chapter 21 1. Extending Python ●
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Chapter 23 3. Web services and the
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Python Keywords Table B.1 lists Pyt
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[a] Boolean comparisons return eith
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% Modulo/remainder • • • •
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isnumeric() • isspace() • istit
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String Format Operator Conversion S
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- Use left justification + Use a pl
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string.isdigit() [b] [c] Returns tr
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List Type Built-in Methods In Table
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[c] New in Python 2.3. [d] New in P
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s.copy() Copy operation: return (sh
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[d] Encoding that this file useswhe
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OverflowError Calculation exceeded
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[i] Warning about FutureWarning con
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[a] Get attribute; getattr() built-
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__radd__, or __iadd__. [f] New in P
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= • • • • • • • •
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Index [SYMBOL] [A] [B] [C] [D] [E]
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| (pipe symbol) 2nd 3rd |= (pipe eq
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arguments class methods command-lin
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instance attributes vs. methods mod
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compound statements concatenation (
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copy( ) creating 2nd dict( ) exact
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sys module try statement with multi
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float( ) built-in function 2nd floa
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eturn values standard type 2nd vari
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grouping 2nd groups( ) method GTK+
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installing Python instance attribut
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through files iterators about any n
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list( ) built-in function 2nd list(
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for re module group(s) invoking 2nd
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modulus operator MRO [See method re
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and OOP classic classes vs. descrip
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intersection update ( &= ) key-look
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PyQt PyQtGPL Pyrex Python Enhanceme
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tuple elements/tuples repetition li
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for statement used with keys for 2n
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about as original Internet protocol
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ules for suites static data static
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subtraction ( - ) operator suites 2
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definition of examples exiting glob
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categorizing standard function to c
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Universal NEWLINE Support (UNS) 2nd
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wxGlade wxPython 2nd 3rd wxWidgets
Page 1154 and 1155:
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Core Python Programming (2nd Edition)

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