Core Python Programming (2nd Edition)

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Chapter 22. Extending Python Chapter Topics ● Introduction/Motivation ● Extending Python ❍ Create Application Code ❍ Wrap Code in Boilerplate ❍ Compile ❍ Import and Test ❍ Reference Counting ❍ Threading and the GIL ● Related Topics In this chapter, we will discuss how to take code written externally and integrate that functionality into the Python programming environment. We will first give you motivation for doing this, then take you through the step-by-step process on how to do it. We should point out, though, that because extensions are primarily done in the C language, all of the example code you will see in this section is pure C but is easily portable to C++.
22.1. Introduction/Motivation 22.1.1. What Are Extensions? In general, any code that you write that can be integrated or imported into another Python script can be considered an extension. This new code can be written in pure Python or in a compiled language like C and C++ (or Java for Jython and C# or VisualBasic.NET for IronPython). One great feature of Python is that its extensions interact with the interpreter in exactly the same way as the regular Python modules. Python was designed so that the abstraction of module import hides the underlying implementation details from the code that uses such extensions. Unless the client programmer searches the file system, he or she simply cannot tell whether a module is written in Python or in a compiled language. Core Note: Creating extensions on different platforms We will note here that extensions are generally available in a development environment where you compile your own Python interpreter. There is a subtle relationship between manual compilation versus obtaining the binaries. Although compilation may be a bit trickier than just downloading and installing binaries, you have the most flexibility in customizing the version of Python you are using. If you intend to create extensions, you should perform this task in a similar environment. The examples in this chapter are built on a Unix-based system (which usually comes with a compilers), but, assuming you do have access to a C/C++ (or Java) compiler and a Python development environment in C/C++ (or Java), the only differences are in your compilation method. The actual code to make your extensions usable in the Python world is the same on any platform. If you are developing on a Win32 platform, you will need Visual C++ "Developer Studio." The Python distribution comes with project files for version 7.1, but you may use older versions of VC++. More information on building extensions on Win32 can be found at: http://docs.python.org/ext/building-on-windows.html Caution:Although we know enough not to move binaries between different hosts, it is also a good idea just to compile on the same box and not move extensions between boxes either, even if they are of the same architecture. Sometimes slight differences of compiler or CPU will cause code not to work consistently. 22.1.2. Why Extend Python? Throughout the brief history of software engineering, programming languages have always been taken at face value. What you see is what you get; it was impossible to add new functionality to an existing language. In today's programming environment, however, the ability to customize one's programming environment is now a desired feature; it also promotes code reuse. Languages such as TCL and Python are among the first languages to provide the ability to extend the base language. So why would you want to extend a language like Python, which is already feature-rich? There are several good reasons:
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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
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20.4. CGI: Helping Web Servers Proc
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Finally, as you can probably guess,
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This HTML file presents a form to t
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Example 20.4. Results Screen CGI co
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Both friends.html and friends1.py a
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The other reason for creating actio
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12 ERROR 13 %s 14 16 ''' 17 18 def
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link with all the existing informat
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Now the user is able to make change
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This script outputs Unicode strings
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When more than one checkbox is subm
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Figure 20-16. Submitting our advanc
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Figure 20-17. Results page generate
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This script has one main class that
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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 932 and 933: DatabaseError Database error DataEr
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 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
Page 982 and 983: 22.4. Exercises 22-1. Extending Pyt
Page 984 and 985: 23.1. Web Services There are many W
Page 986 and 987: The field names are given in the or
Page 988 and 989: 23.2. Programming Microsoft Office
Page 990 and 991: This script launches Excel and writ
Page 992 and 993: 23.2.3. Microsoft Word The next dem
Page 994 and 995: Applying PowerPoint in an applicati
Page 996 and 997: This script launches Outlook, creat
Page 998 and 999: Then when you are trying to send a
Page 1000 and 1001: Lines 113 We import all of the attr
Page 1002 and 1003: 23.3. Python and Java Programming w
Page 1004 and 1005: Example 23.8. Swing "Hello World" i
Page 1006 and 1007: 23.4. Exercises Web Services 23-1.
Page 1008 and 1009: 23-15. Excel Cell Formatting. In th
Page 1010 and 1011: 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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