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Exception Gotchas 627String Exceptions Match by Identity, Not by Value 628Catching the Wrong Thing 629Core Language Summary 629The <strong>Python</strong> Toolset 630Development Tools for Larger Projects 631Chapter Summary 634Brain Builder 635Chapter Quiz 635Quiz Answers 635Brain Builder: Part VII Exercises 636Part VIII. AppendixesA. Installation and Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 639B. Solutions to End-of-Part Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 646Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 681xxviii | Table of Contents
Page 2 and 3: Learning Python
Page 4 and 5: THIRD EDITIONLearning PythonMark Lu
Page 6: To Vera.You are my life.
Page 10 and 11: 3. How You Run Programs . . . . . .
Page 12 and 13: 5. Numbers . . . . . . . . . . . .
Page 14 and 15: 8. Lists and Dictionaries . . . . .
Page 16 and 17: Statement rule special cases 208Blo
Page 18 and 19: Iterators: A First Look 258File Ite
Page 20 and 21: Scopes and Nested Functions 320Nest
Page 22 and 23: How Imports Work 3891. Find It 390T
Page 24 and 25: Brain Builder 445Chapter Quiz 445Qu
Page 26: 25. Designing with Classes . . . .
Page 31 and 32: • Generator expressions (Chapter
Page 33 and 34: This Edition’s Scope ChangesThis
Page 35 and 36: people already familiar with applic
Page 37 and 38: Part VIII, AppendixesThe book ends
Page 39 and 40: • Octal and binary literals: the
Page 41 and 42: Although this list may seem somewha
Page 43 and 44: Safari® Books OnlineWhen you see a
Page 45 and 46: I also want to thank my original ed
Page 48 and 49: Chapter 1CHAPTER 1A Python Q&A Sess
Page 50 and 51: Software QualityBy design, Python m
Page 52 and 53: it allows programs to scale up in s
Page 54 and 55: writing software, whether for short
Page 56 and 57: frameworks, such as Python’s COM
Page 58 and 59: It’s FreePython is completely fre
Page 60 and 61: Built-in toolsTo process all those
Page 62 and 63: Consider this: when people create a
Page 64 and 65: Especially for programs that do mor
Page 66 and 67: 4. You can use Python for nearly an
Page 68 and 69: Python installation details vary by
Page 70 and 71: We’ve just run a Python script th
Page 72 and 73: This is why some Python code may no
Page 74 and 75: IronPythonA third (and, at this wri
Page 76 and 77: further detail here. Initial result
Page 78 and 79:
B RAINB UILDERChapter Quiz1. What i
Page 80 and 81:
Typing the word “python” at you
Page 82 and 83:
Using the Interactive PromptAlthoug
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Notice that the module file is call
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Unix Executable Scripts (#!)If you
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# A commentimport sysprint sys.plat
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your top-level files if and only if
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The reload function expects the nam
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from threenames import a, b, c # Co
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Windows, X Windows (for Linux, Unix
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• You must add “.py” explicit
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already familiar with a command-lin
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you would launch any other executab
Page 104 and 105:
B RAINB UILDERChapter Quiz1. How ca
Page 106 and 107:
B RAINB UILDERPart I ExercisesIt’
Page 108:
PART IIII.Types and Operations
Page 111 and 112:
Why Use Built-in Types?If you’ve
Page 113 and 114:
list. As you’ll learn, Python is
Page 115 and 116:
Sequence OperationsAs sequences, st
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one of its positions, but you can a
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The dir function simply gives the m
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Sequence OperationsBecause they are
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The first operation here fetches th
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Although the curly-braces literal f
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As mentioned earlier, because dicti
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will be quick enough as it is. If y
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This creates a file in the current
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How to Break Your Code’s Flexibil
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Moreover, keep in mind that the obj
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6. “Polymorphism” means that th
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Numeric LiteralsAmong its basic typ
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Python Expression OperatorsPerhaps
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Python ranks the complexity of nume
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2 + 4.0, 2.0 ** b # Mixed-type conv
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Division: Classic, Floor, and TrueN
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The L at the end of the digit strin
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Other Built-in Numeric ToolsIn addi
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mixed in expressions, Python conver
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Because of this customization, as o
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ChapterCHAPTER66The Dynamic Typing
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These links from variables to objec
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First, notice that x is set to a di
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One way to think of this is that, u
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Because Python caches and reuses sm
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B RAINB UILDERChapter Quiz1. Consid
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Table 7-1. Common string literals a
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The two characters \n stand for a s
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escapes can lead to trouble. It’s
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I said this was hackish because Pyt
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Strings in ActionIn Python 3.0, the
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The first line defines a four-chara
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You can also use a negative stride.
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int(S) + I # Force addition43>>> S
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garbage collects (reclaims the spac
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The character codes in Table 7-3 sh
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Putting these two together allows u
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change strings. If you have to appl
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'Ni' in lineTrue>>> sub = 'Ni!\n'>>
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at work on strings—concatenation,
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ChapterCHAPTER88Lists and Dictionar
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Table 8-1. Common list literals and
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For example, one of the simplest wa
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Perhaps the most commonly used list
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Python’s manuals, Python’s dir
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a dictionary, it stores its items i
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Such lists are useful in loops that
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Dictionary Usage NotesDictionaries
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try:... print Matrix[(2,3,6)] # Try
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As suggested near the end of Table
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ChapterCHAPTER99Tuples, Files, and
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T = (1, 2, 3, 4) # Indexing, slicin
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Tuples can also be used in places t
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Calling the file close method termi
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As we have learned, int translates
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Binary data files are advanced and
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Let’s look at an example of nesti
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For example, say you have a list an
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Here, L1 is greater than L2 because
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NumbersCollectionsIntegersFloatSequ
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This effect usually becomes importa
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We also learned that files are retu
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B RAINB UILDERPart II ExercisesThis
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8. String indexing. Define a string
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Chapter 10CHAPTER 10Introducing Pyt
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Table 10-1. Python statements (cont
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In Python, the general rule is that
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while (x > 0) {--------;--------;--
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dictionary braces ({}). Any code en
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• The raw_input built-in function
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We’ll study the if statement in m
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Chapter SummaryThat concludes our q
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Chapter 11CHAPTER 11Assignment, Exp
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Multiple-target assignmentsThe fift
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As the last example in this interac
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issue, initialize mutable objects i
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L += [9, 10] # Mapped to L.extend([
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Naming conventionsBesides these rul
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Expression Statements and In-Place
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This code explicitly calls the writ
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This extended form of print is also
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B RAINB UILDERChapter Quiz1. Name t
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else:# Optional elseBasic ExamplesT
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Although dictionary-based multiway
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In general, top-level (unnested) co
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Truth TestsThe notions of compariso
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variable. For these reasons (and, f
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B RAINB UILDERChapter Quiz1. How mi
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General FormatIn its most complex f
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ExamplesLet’s turn to a few simpl
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x = y / 2 # For some y > 1while x >
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Why You Will Care: Emulating C whil
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In fact, as we’ll see in a moment
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Why You Will Care: File ScannersIn
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f.next( )'print sys.path\n'>>> f.ne
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In recent versions of Python, thoug
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Loop Coding TechniquesThe for loop
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for instead of while whenever possi
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for (x, y) in zip(L1, L2):... print
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Generating Both Offsets and Items:
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es = []>>> for x in L:... res.appen
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For example, the following builds a
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6. The best way to read lines from
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As summarized in Table 14-1, there
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User-defined docstringsFor example,
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You can also read about built-in fu
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help(docstrings.square)Help on func
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Figure 14-2. When you find a module
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Cool PyDoc trick of the day: if you
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Common Coding GotchasBefore the pro
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Chapter SummaryThis chapter took us
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B RAINB UILDERPart III ExercisesNow
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PART IVIV.Functions
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Why Use Functions?Before we get int
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• Arguments, return values, and v
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DefinitionHere’s a definition typ
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A Second Example: Intersecting Sequ
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Local VariablesThe variable res ins
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ChapterCHAPTER1616Scopes and Argume
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• Each call to a function creates
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Scope ExampleLet’s look at a larg
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Functions can similarly hide global
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Python—local variables disappear
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def test( ):print varlocal(); glob1
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(described in Part VI) are usually
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If you avoid nesting this way, you
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Arbitrary scope nestingBefore endin
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Figure 16-2 illustrates the name/ob
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can usually simulate it by returnin
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Special matching modes let you be f
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Collecting argumentsThe first use,
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The min Wakeup CallTo make this mor
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eval built-in function (see the lib
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If you mix arguments in any other o
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ChapterCHAPTER1717Advanced Function
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act = knights( )>>> act('robin')'Si
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Because expressions like these can
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Applying Functions to ArgumentsSome
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Mapping Functions over Sequences: m
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Items in the sequence for which the
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List comprehensions collect the res
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Finally, here is a much more comple
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Comprehending List ComprehensionsWi
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The chief code difference between g
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However, generators allow functions
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Traceback (most recent call last):F
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When I ran this in IDLE on Windows
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• Coupling: avoid changing variab
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Local Names Are Detected Statically
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saver( )[1, 1, 1]Some see this beha
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here because they are just as relat
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6. The map call is similar to a lis
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oth arguments, feel free to pick a
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PART VV.Modules
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object. As we saw in the last part
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For instance, suppose the file b.py
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To better understand module imports
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and then only if you must import ac
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at import time when a .zip file is
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As this chapter demonstrated, the i
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ChapterCHAPTER1919Module Coding Bas
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The from statementBy contrast, beca
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Here, x is not a shared mutable obj
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Probably the best real-world advice
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The first time this module is impor
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The second module, modb.py, defines
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doesn’t help in every situation,
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eload(changer) # Forces new code to
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B RAINB UILDERChapter Quiz1. How do
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Furthermore, these imports imply th
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from * statement behaviorAs an adva
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in the next chapter, can also help
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Now the problem starts to materiali
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Chapter SummaryThis chapter introdu
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ChapterCHAPTER2121Advanced Module T
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Mixed Usage Modes: _ _name_ _ and _
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But, if we import the file, its nam
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For example, presently, a statement
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This form imports the string module
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For instance, to get to an attribut
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Generally, forward references are o
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If we use import to get the whole m
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As you can see, there are problems
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import recur1Traceback (innermost l
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B RAINB UILDERPart V ExercisesSee
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PART VIVI.Classes and OOP
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Why Use Classes?Remember when I tol
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In Python, this is all very literal
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The primary difference between clas
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I1.setname('bob')I2.setname('mel')p
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As an example, suppose you’re ass
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you often simply code a subclass th
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6. You create a class instance by c
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The following is a quick summary of
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X- dataY- datais-ais-aFirstClass- s
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The net effect, and the main purpos
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...class spam:...class ham:...class
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A Third ExampleOn to another exampl
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you might code. In fact, even thoug
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There is nothing about a class here
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5. self is the name commonly given
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def method(self,...):self.member =
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1 spam2 spamThe net result is that
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Calling Superclass ConstructorsMeth
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The net result is a tree of attribu
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print '\nProvider...'x = Provider(
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As discussed previously, the _ _ini
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In fact, it’s really a case of
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Notice that this example would prob
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produce just one value at a time, w
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class Test1(Privacy):privates = ['a
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In practice, _ _str_ _ (or its low-
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Now, in the context of a GUI, we ca
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Namespaces: The Whole StoryNow that
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The outputs that are printed when t
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super._ _dict_ _{'_ _module_ _': '_
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superclasses that have empty _ _bas
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if _ _name_ _ == '_ _main_ _':bob =
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ChapterCHAPTER2525Designing with Cl
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This code emulates tools like recor
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of Employee. In OOP terms, we call
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class PizzaShop:def _ _init_ _(self
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To process different sorts of strea
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attributes, a wrapper class (someti
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the instance’s memory address by
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Classes Are Objects: Generic Object
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Methods Are Objects: Bound or Unbou
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def method(self, arg):"I am: spam.m
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Extending Types by EmbeddingRemembe
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lists to add just methods and opera
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Name mangling happens only in class
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New-style classes are almost comple
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Here, a tree of classic classes is
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x = limiter( )>>> x.age # Must assi
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... if name == 'age':... self._ _di
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spam.printNumInstances( )Number of
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spans all instances generated from
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Decorator ExampleHere is an example
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Is this a useful feature or a dange
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Classes introduce local scopes, jus
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when used well. However, you’ll s
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B RAINB UILDERPart VI ExercisesThes
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f. How would you go about emulating
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AnimalMammalCatDogPrimateHackerFigu
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OtherAnd, of course, the number one
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Chapter 27CHAPTER 27Exception Basic
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Event notificationExceptions can al
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This time, after the exception is c
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In practice, try/except combination
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finally clauses run on the way out,
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The try/else ClauseAt first glance,
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Sometimes, though, you’ll want to
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This particular example’s functio
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Again, the finally block is always
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So, what’s an exception name? It
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Running a raise this way reraises t
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The expression here is assumed to r
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Why You Will Care: Error ChecksOne
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String-Based ExceptionsIn all the e
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def raiser1( ):X = Specific1( )rais
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Now, when people use your library,
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maintenance issues than strings do.
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As we learned earlier, the _ _repr_
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try:parser( )except FormatError, ex
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Chapter SummaryIn this chapter, we
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Chapter 29CHAPTER 29Designing with
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Example: Control-Flow NestingLet’
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finally runfinally runTraceback (mo
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In the following, the empty except
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• However, there are exceptions t
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As a rule of thumb, be as specific
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... print 'got it'...got itThis wor
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Development Tools for Larger Projec
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encountered. Because IDEs such as I
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B RAINB UILDERChapter Quiz1. (This
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PART VIIIVIII.Appendixes
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You can always fetch the latest and
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The Python 2.5 MSI Installer on Win
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Getting Tkinter (and IDLE) GUI Supp
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AppendixAPPENDIXBBSolutions to End-
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The reason for the cycle is subtle
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2. Indexing and slicing. Indexing o
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7. Generic operations. Question ans
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Part III, Statements and SyntaxSee
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if (2 ** X) in L:print (2 ** X), 'w
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print adder( )print adder(5)print a
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print y, 'not prime'else:x = y // 2
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Incidentally, to do the “ambitiou
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C:\Python25> python>>> import mypkg
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2. Operator overloading. The soluti
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... def _ _setattr_ _(self, name, v
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x.intersect([1,2,3], [2,3,4], [1,2,
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9. The Dead Parrot Sketch. Here’s
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import oopssafe(oops.oops)% python
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for line in open(filename):cols = l
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class MySubGui(MyGui):colors = ['bl
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# Database script to populate a she
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ArithmeticError (built-in exception
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classes (continued)objects (see obj
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end of line, 204enumerate function,
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files (continued)manual close, 177o
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inheritance (continued)example, 547
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loops (continued)list comprehension
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object persistence, 86object types,
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Python (continued)gaming, images, A
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strings (continued)immutability, 71
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Vvan Rossum, Guido, 18, 546varargs,
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