Is Python a

More documents

Recommendations

Info

B RAINB UILDERChapter Quiz1. What is the Python interpreter?2. What is source code?3. What is byte code?4. What is the PVM?5. Name two variations on Python’s standard execution model.6. How are CPython, Jython, and IronPython different?Quiz Answers1. The Python interpreter is a program that runs the Python programs you write.2. Source code is the statements you write for your program—it consists of text intext files that normally end with a .py extension.3. Byte code is the lower-level form of your program after Python compiles it.Python automatically stores byte code in files with a .pyc extension.4. The PVM is the Python Virtual Machine—the runtime engine of Python thatinterprets your compiled code.5. Psyco, Shedskin, and frozen binaries are all variations on the execution model.6. CPython is the standard implementation of the language. Jython and IronPythonimplement Python programs for use in Java and .NET environments, respectively;they are alternative compilers for Python.Chapter Quiz | 33
ChapterCHAPTER33How You Run Programs 3OK, it’s time to start running some code. Now that you have a handle on programexecution, you’re finally ready to start some real Python programming. At this point,I’ll assume that you have Python installed on your computer; if not, see the priorchapter and Appendix A for installation and configuration hints.There are a variety of ways to tell Python to execute the code you type. This chapterdiscusses all the program-launching techniques in common use today. Along theway, you’ll learn how to type code interactively, and how to save it in files to be runwith system command lines, icon clicks, module imports, IDE GUIs such as IDLEand Eclipse, and more.If you just want to find out how to run a Python program quickly, you may betempted to read the parts that pertain only to your platform and move on toChapter 4. But don’t skip the material on module imports, as that’s essential tounderstanding Python’s program architecture. I also encourage you at least to skimthe sections on IDLE and other IDEs, so you’ll know what tools are available forwhen you start developing more sophisticated Python programs.Interactive CodingPerhaps the simplest way to run Python programs is to type them at Python’s interactivecommand line. There are a variety of ways to start this command line—in anIDE, from a system console, and so on. Assuming the interpreter is installed as anexecutable program on your system, the most platform-neutral way to start an interactiveinterpreter session is usually just to type python at your operating system’sprompt, without any arguments. For example:% pythonPython 2.5 (r25:51908, Sep 19 2006, 09:52:17) [MSC v.1310 32 bit (Intel)] on win32Type "help", "copyright", "credits" or "license" for more information.>>>34
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 30 and 31: Preface1This book provides an intro
Page 32 and 33: In addition, this entire edition in
Page 34 and 35: This book is designed to be an intr
Page 36 and 37: Part I, Getting StartedWe begin wit
Page 38 and 39: Preparing for Python 3.0The first a
Page 40 and 41: • In the iterator protocol, the X
Page 42 and 43: We appreciate, but do not require,
Page 44 and 45: It’s been a long and winding road
Page 46: PART II.Getting Started
Page 49 and 50: Developer productivityPython boosts
Page 51 and 52: Is Python a “Scripting Language
Page 53 and 54: Who Uses Python Today?At this writi
Page 55 and 56: (both Classic and OS X). A free ext
Page 57 and 58: Gaming, Images, AI, XML, Robots, an
Page 59 and 60: Besides the language interpreter it
Page 61 and 62: Python Is Engineering, Not ArtWhen
Page 63 and 64: world, the truth is that Python cre
Page 65 and 66: B RAINB UILDERChapter QuizIn this e
Page 67 and 68: ChapterCHAPTER22How Python Runs Pro
Page 69 and 70: Because installation details are so
Page 71 and 72: If Python cannot write the byte cod
Page 73 and 74: Python Implementation AlternativesR
Page 75 and 76: Roughly, while your program runs, P
Page 77: Future Possibilities?Finally, note
Page 81 and 82: Here, the last two lines typed are
Page 83 and 84: un it again without retyping it fro
Page 85 and 86: Using Command Lines and FilesRunnin
Page 87 and 88: In this case, you don’t need the
Page 89 and 90: The raw_input TrickUnfortunately, o
Page 91 and 92: In simple terms, every file of Pyth
Page 93 and 94: Alternatively, you can fetch (reall
Page 95 and 96: Because of these complications (and
Page 97 and 98: Figure 3-3. The main Python shell w
Page 99 and 100: start occasionally on some Windows
Page 101 and 102: Embedding CallsAt this point, we’
Page 103 and 104: Which Option Should I Use?With all
Page 105 and 106: 6. IDLE can still be hung by some t
Page 107 and 108: 5. Errors. Experiment with typing m
Page 110 and 111: Chapter 4CHAPTER 4Introducing Pytho
Page 112 and 113: Python’s Core Data TypesTable 4-1
Page 114 and 115: print the result—with more than 3
Page 116 and 117: In a slice, the left bound defaults
Page 118 and 119: S = 'spam'>>> S.upper( ) # Upper- a
Page 120 and 121: msg'\naaaaaaaaaaaaa\nbbb\'\'\'bbbbb
Page 122 and 123: M.reverse( )>>> M['cc', 'bb', 'aa']
Page 124 and 125: diag = [M[i][i] for i in [0, 1, 2]]
Page 126 and 127: ec['job'][-1] # Index the nested li
Page 128 and 129:
on any object that is a sequence an
Page 130 and 131:
TuplesThe tuple object (pronounced
Page 132 and 133:
Other Core TypesBeyond the core typ
Page 134 and 135:
def lastName(self):return self.name
Page 136 and 137:
B RAINB UILDERChapter QuizWe’ll e
Page 138 and 139:
Chapter 5CHAPTER 5Numbers5This chap
Page 140 and 141:
Hexadecimal and octal literalsThe r
Page 142 and 143:
Mixed Operators Follow Operator Pre
Page 144 and 145:
Numbers in ActionProbably the best
Page 146 and 147:
(2.0 + a) # Auto echo output: more
Page 148 and 149:
(9 / 3), (9.0 / 3), (9 // 3), (9 //
Page 150 and 151:
Hexadecimal and Octal NotationAs me
Page 152 and 153:
The random module can be useful for
Page 154 and 155:
Such operations are convenient when
Page 156 and 157:
B RAINB UILDERChapter Quiz1. What i
Page 158 and 159:
Python to use the name a as a varia
Page 160 and 161:
However, that’s not really what
Page 162 and 163:
Names References Objectsa=3b=aa 3bF
Page 164 and 165:
changes, they can impact other part
Page 166 and 167:
import sys>>> sys.getrefcount(1) #
Page 168 and 169:
Chapter 7CHAPTER 7Strings7The next
Page 170 and 171:
Single- and Double-Quoted Strings A
Page 172 and 173:
Some escape sequences allow you to
Page 174 and 175:
Triple Quotes Code Multiline Block
Page 176 and 177:
Because Unicode is designed to hand
Page 178 and 179:
Notice that operator overloading is
Page 180 and 181:
• Indexing (S[i]) fetches compone
Page 182 and 183:
Why You Will Care: SlicesThroughout
Page 184 and 185:
Such conversions can be used in con
Page 186 and 187:
The third example again inserts thr
Page 188 and 189:
eply = """Greetings...Hello %(name)
Page 190 and 191:
S = 'spammy'>>> S = S[:3] + 'xx' +
Page 192 and 193:
can pull out its components by spli
Page 194 and 195:
x'aspambspamcspam'To access the sam
Page 196 and 197:
B RAINB UILDERChapter Quiz1. Can th
Page 198 and 199:
Variable-length, heterogeneous, and
Page 200 and 201:
espond to all of the general sequen
Page 202 and 203:
Both index and slice assignments ar
Page 204 and 205:
In some types of programs, the list
Page 206 and 207:
Tables of object references (hash t
Page 208 and 209:
Later in this chapter and book, you
Page 210 and 211:
Dictionaries also provide a copy me
Page 212 and 213:
Here, it looks as if D is a 100-ite
Page 214 and 215:
Other ways to make dictionariesFina
Page 216 and 217:
B RAINB UILDERChapter Quiz1. Name t
Page 218 and 219:
Of the category immutable sequenceL
Page 220 and 221:
T = tuple(tmp) # Make a tuple from
Page 222 and 223:
Table 9-2. Common file operations (
Page 224 and 225:
F.write('%s,%s,%s\n' % (X, Y, Z)) #
Page 226 and 227:
We get back an equivalent dictionar
Page 228 and 229:
Why You Will Care: Operator Overloa
Page 230 and 231:
We studied this phenomenon in Chapt
Page 232 and 233:
For instance, a comparison of list
Page 234 and 235:
Python also provides a special obje
Page 236 and 237:
Because types can be subclassed in
Page 238 and 239:
Beware of Cyclic Data StructuresWe
Page 240 and 241:
B RAINB UILDERChapter Quiz1. How ca
Page 242 and 243:
c. Finally, how does Python handle
Page 244:
PART IIIIII.Statements and Syntax
Page 247 and 248:
Python’s StatementsTable 10-1 sum
Page 249 and 250:
What Python AddsThe one new syntax
Page 251 and 252:
Why Indentation Syntax?The indentat
Page 253 and 254:
My point is that even when a langua
Page 255 and 256:
prints, function calls, and the lik
Page 257 and 258:
Armed with this information, we can
Page 259 and 260:
an except part that gives the excep
Page 261 and 262:
B RAINB UILDERChapter Quiz1. What t
Page 263 and 264:
• Implicit assignments: import, f
Page 265 and 266:
In fact, the original tuple and lis
Page 267 and 268:
Notice that this code is using the
Page 269 and 270:
Augmented assignments have three ad
Page 271 and 272:
Reserved words are off-limitsNames
Page 273 and 274:
Expression StatementsIn Python, you
Page 275 and 276:
Table 11-5. print statement formsOp
Page 277 and 278:
The print >> file ExtensionThis tri
Page 279 and 280:
In Python 3.0, the print statement
Page 281 and 282:
ChapterCHAPTER1212if Tests 12This c
Page 283 and 284:
If you’ve used languages like C o
Page 285 and 286:
As you’ve seen, there are no vari
Page 287 and 288:
• Triple-quoted string literals c
Page 289 and 290:
[ ] or 33>>> [ ] or { }{ }In the fi
Page 291 and 292:
of Python 2.5. Again, though, you s
Page 293 and 294:
ChapterCHAPTER1313while and for Loo
Page 295 and 296:
Finally, notice that Python doesn
Page 297 and 298:
Because continue jumps to the top o
Page 299 and 300:
print 'Ni'breakx = x[1:]else:print
Page 301 and 302:
ExamplesLet’s type a few for loop
Page 303 and 304:
Note that this example is easier to
Page 305 and 306:
eadlines loads a file all at once i
Page 307 and 308:
Moreover, the iterator version has
Page 309 and 310:
We saw the sorted function used her
Page 311 and 312:
Although such range results may be
Page 313 and 314:
To really change the list as we mar
Page 315 and 316:
Dictionary construction with zipIn
Page 317 and 318:
List Comprehensions: A First LookIn
Page 319 and 320:
and add it to the result list. Agai
Page 321 and 322:
B RAINB UILDERChapter Quiz1. When i
Page 323 and 324:
ChapterCHAPTER1414The Documentation
Page 325 and 326:
Only some of the many names are dis
Page 327 and 328:
Note that you will generally want t
Page 329 and 330:
FILE(built-in)DESCRIPTIONThis modul
Page 331 and 332:
too). Enter the name of a module yo
Page 333 and 334:
Figure 14-3. PyDoc can serve up doc
Page 335 and 336:
Figure 14-4. Python’s standard ma
Page 337 and 338:
• Use simple for loops instead of
Page 339 and 340:
B RAINB UILDERChapter Quiz1. When s
Page 341 and 342:
if found:print 'at index', ielse:pr
Page 344 and 345:
Chapter 15CHAPTER 15Function Basics
Page 346 and 347:
In this chapter, we will explore ho
Page 348 and 349:
def Executes at RuntimeThe Python d
Page 350 and 351:
Polymorphism in PythonAs we just sa
Page 352 and 353:
s1 = "SPAM">>> s2 = "SCAM">>> inter
Page 354 and 355:
Page 356 and 357:
In all cases, the scope of a variab
Page 358 and 359:
lambdas, then the global (G) scope,
Page 360 and 361:
have to import it in order to inspe
Page 362 and 363:
Here, x, y, and z are all globals i
Page 364 and 365:
Here again, the best prescription i
Page 366 and 367:
Notice that the global declaration
Page 368 and 369:
Retaining enclosing scopes’ state
Page 370 and 371:
def makeActions( ):... acts = []...
Page 372 and 373:
Python’s pass-by-assignment schem
Page 374 and 375:
Avoiding Mutable Argument ChangesAr
Page 376 and 377:
Defaults: specify values for argume
Page 378 and 379:
DefaultsWe talked a little about de
Page 380 and 381:
func(*args)1 2 3 4Similarly, the **
Page 382 and 383:
if arg < res:res = argreturn resdef
Page 384 and 385:
def union(*args):res = []for seq in
Page 386 and 387:
For both scopes and arguments, we a
Page 388 and 389:
Quiz Answers1. The output here is '
Page 390 and 391:
Function objects returned by runnin
Page 392 and 393:
a dictionary becomes a more general
Page 394 and 395:
What wasn’t illustrated in the pr
Page 396 and 397:
around this, simply build up the ar
Page 398 and 399:
Moreover, map can be used in more a
Page 400 and 401:
Together with map, filter and reduc
Page 402 and 403:
... if x % 2 == 0:... res.append(x)
Page 404 and 405:
List comprehensions are powerful to
Page 406 and 407:
Why You Will Care: List Comprehensi
Page 408 and 409:
If you want to see what is going on
Page 410 and 411:
for key in D:... print key, D[key].
Page 412 and 413:
I’ve mentioned a few times that l
Page 414 and 415:
For more insight, try modifying the
Page 416 and 417:
seen some of these uses in earlier
Page 418 and 419:
...>>> selector( )99Remember, thoug
Page 420 and 421:
Functions Without returnsIn Python
Page 422 and 423:
Page 424 and 425:
B RAINB UILDERPart IV ExercisesIn t
Page 426:
Package this code as a reusable fun
Page 430 and 431:
Chapter 18CHAPTER 18Modules: The Bi
Page 432 and 433:
How to Structure a ProgramGenerally
Page 434 and 435:
in any other programs you may write
Page 436 and 437:
Home directoryPython first looks fo
Page 438 and 439:
Module file selectionKeep in mind t
Page 440 and 441:
Because this last import step actua
Page 442 and 443:
B RAINB UILDERChapter Quiz1. How do
Page 444 and 445:
ecause if is a reserved word—when
Page 446 and 447:
As one consequence, because top-lev
Page 448 and 449:
Like all assignments, the from stat
Page 450 and 451:
Files Generate NamespacesSo, how do
Page 452 and 453:
Qualification is really an expressi
Page 454 and 455:
X = 1import mod2print X,print mod2.
Page 456 and 457:
• Reloads impact all clients that
Page 458 and 459:
Although we’ve already seen enoug
Page 460 and 461:
Chapter 20CHAPTER 20Module Packages
Page 462 and 463:
dir0\dir1\dir2\mod.pyand an import
Page 464 and 465:
import dir1.dir2.mod # Later import
Page 466 and 467:
A Tale of Three SystemsThe only tim
Page 468 and 469:
Also, notice in the install hierarc
Page 470 and 471:
Page 472 and 473:
from * copies out all names, the im
Page 474 and 475:
Unit Tests with _ _name_ _In fact,
Page 476 and 477:
of a running Python program, and so
Page 478 and 479:
This defines a package named mypkg
Page 480 and 481:
• Modules should rarely change ot
Page 482 and 483:
We’ve also provided self-test log
Page 484 and 485:
To get around this, you need to use
Page 486 and 487:
from module import X. . .reload(mod
Page 488 and 489:
import typesdef status(module):prin
Page 490 and 491:
Page 492:
5. Package imports. Import your fil
Page 496 and 497:
Chapter 22CHAPTER 22OOP: The Big Pi
Page 498 and 499:
Customization via inheritanceClasse
Page 500 and 501:
ecause the search proceeds bottom-u
Page 502 and 503:
• Each class statement generates
Page 504 and 505:
The _ _init_ _ method is known as t
Page 506 and 507:
This is yet another instance of the
Page 508 and 509:
Page 510 and 511:
Chapter 23CHAPTER 23Class Coding Ba
Page 512 and 513:
A First ExampleLet’s turn to a re
Page 514 and 515:
Although less common, we could even
Page 516 and 517:
Z (instance)- datais-aSecondClass-
Page 518 and 519:
foster object interfaces that are m
Page 520 and 521:
Specially named methods such as _ _
Page 522 and 523:
Really, these instances have no att
Page 524 and 525:
B RAINB UILDERChapter Quiz1. How ar
Page 526 and 527:
Chapter 24CHAPTER 24Class Coding De
Page 528 and 529:
Here, because the name spam is assi
Page 530 and 531:
always go through self to fetch or
Page 532 and 533:
In Python, inheritance happens when
Page 534 and 535:
This extension coding pattern is al
Page 536 and 537:
def delegate(self):self.action( )de
Page 538 and 539:
All operator overloading methods ar
Page 540 and 541:
def _ _iter_ _(self): # Get iterato
Page 542 and 543:
class SkipIterator:def _ _init_ _(s
Page 544 and 545:
makes age look like a real attribut
Page 546 and 547:
class addrepr(adder): # Inherit _ _
Page 548 and 549:
class Prod:... def _ _init_ _(self,
Page 550 and 551:
You’ll also see another _ _call_
Page 552 and 553:
principle translates to code, and s
Page 554 and 555:
To help you understand how attribut
Page 556 and 557:
X._ _dict_ _{'data1': 'spam', 'data
Page 558 and 559:
every attribute in the instance. It
Page 560 and 561:
JonesTrace through the code in this
Page 562 and 563:
6. Printing sue ultimately runs the
Page 564 and 565:
Overloading by Call Signatures (or
Page 566 and 567:
mark = Person('ml', 'trainer')>>> d
Page 568 and 569:
Employee does stuffChef makes foodS
Page 570 and 571:
def processor(reader, converter, wr
Page 572 and 573:
Because composition is a design iss
Page 574 and 575:
Multiple InheritanceIn a class stat
Page 576 and 577:
if __name__ == "_ _main_ _":X = Sub
Page 578 and 579:
Why Factories?So what good is the f
Page 580 and 581:
On the other hand, if we qualify th
Page 582 and 583:
docstr.func._ _doc_ _'I am: docstr.
Page 584 and 585:
Chapter 26CHAPTER 26Advanced Class
Page 586 and 587:
This change allows you to customize
Page 588 and 589:
explored in Chapter 5; this type pr
Page 590 and 591:
class C2:def metha(self): self._ _X
Page 592 and 593:
Diamond inheritance exampleTo illus
Page 594 and 595:
ensures that your code won’t vary
Page 596 and 597:
x = classic( )>>> x.age # Runs _ _g
Page 598 and 599:
class attributes instead of instanc
Page 600 and 601:
such methods, classes call the buil
Page 602 and 603:
Python provides some built-in funct
Page 604 and 605:
Class GotchasMost class issues can
Page 606 and 607:
in which we list them in the class
Page 608 and 609:
A better alternative would be to re
Page 610 and 611:
B RAINB UILDERChapter Quiz1. Name t
Page 612 and 613:
c. Is there a general way to route
Page 614 and 615:
The order simulation works as follo
Page 616 and 617:
Why You Will Care: OOP by the Maste
Page 618:
PART VIIVII.Exceptions and Tools
Page 621 and 622:
Why Use Exceptions?In a nutshell, e
Page 623 and 624:
However, if we ask this function to
Page 625 and 626:
... print 'after fetch'...'m'after
Page 627 and 628:
except , :except (name3, name4):exc
Page 629 and 630:
uns the statements under the first
Page 631 and 632:
def gosouth(x):print gobad(x, 0)gos
Page 633 and 634:
• If an exception does occur duri
Page 635 and 636:
The code in this statement’s main
Page 637 and 638:
When this code is run, the followin
Page 639 and 640:
the globals reside in. Passing extr
Page 641 and 642:
traps programming errors itself, th
Page 643 and 644:
The Context Management ProtocolThe
Page 645 and 646:
Notice that this class’ _ _exit_
Page 647 and 648:
ChapterCHAPTER2828Exception Objects
Page 649 and 650:
Class-Based ExceptionsStrings are a
Page 651 and 652:
Why Class Exceptions?Because there
Page 653 and 654:
But this workaround might catch mor
Page 655 and 656:
except StandardError:...handle Pyth
Page 657 and 658:
def parser( ):... # when error foun
Page 659 and 660:
aise instanceraise class, instance#
Page 661 and 662:
B RAINB UILDERChapter Quiz1. How ar
Page 663 and 664:
try:func1()except E:...def func1():
Page 665 and 666:
Really, this code just sets up the
Page 667 and 668:
Functions Signal Conditions with ra
Page 669 and 670:
At the end of this chapter, we’ll
Page 671 and 672:
For example, scripts normally exit
Page 673 and 674:
String Exceptions Match by Identity
Page 675 and 676:
The Python ToolsetFrom this point f
Page 677 and 678:
DoctestThe doctest standard library
Page 679 and 680:
To learn about other large-scale Py
Page 681 and 682:
B RAINB UILDERPart VII ExercisesAs
Page 684 and 685:
Appendix AAPPENDIX AInstallation an
Page 686 and 687:
When installed on Windows, Python a
Page 688 and 689:
These variables are straightforward
Page 690 and 691:
eboot your machine for the changes
Page 692 and 693:
Python’s search path. The .pyc fi
Page 694 and 695:
S = "ham">>> "eggs " + S'eggs ham'>
Page 696 and 697:
4. Tuple assignment. The values of
Page 698 and 699:
9. Immutable types. Either of the f
Page 700 and 701:
a => 1b => 2c => 3d => 4e => 5f =>
Page 702 and 703:
3. varargs. Two alternative adder f
Page 704 and 705:
7. More argument-matching examples.
Page 706 and 707:
es[1.4142135623730951, 2.0, 3.0, 4.
Page 708 and 709:
% python myclient.py13 346As for th
Page 710 and 711:
% python>>> from adder import *>>>
Page 712 and 713:
Note that it’s important to copy
Page 714 and 715:
My solution to the multiple-operand
Page 716 and 717:
class Customer:def _ _init_ _(self)
Page 718 and 719:
if _ _name_ _ == '_ _main_ _': doom
Page 720 and 721:
allsizes.sort( )print allsizes[:2]p
Page 722 and 723:
win = Tk( )L = Label(win, text='Spa
Page 724 and 725:
# CGI client-side script to interac
Page 726 and 727:
IndexSymbols# comments, 279% (remai
Page 728 and 729:
ord function, 355pow function, 353r
Page 730 and 731:
delegation, 527-528, 556descriptor
Page 732 and 733:
Part I - Modules, 646Part I - Progr
Page 734 and 735:
Hhandler, 578“has-a” relationsh
Page 736 and 737:
Kkeyed-access files, 86KeyError (bu
Page 738 and 739:
imports and reloads, 45-50example,
Page 740 and 741:
overloading by call signatures, 519
Page 742 and 743:
cross-file changes, minimizing, 318
Page 744 and 745:
Tkinter, 9, 31environment setting,
Page 746:
About the AuthorMark Lutz is the wo
show all

Is Python a

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?