Beginning Python - From Novice to Professional

More documents

Recommendations

Info

CHAPTER 11 ■ FILES AND STUFF 261 ■Note An alternative to readlines that can be useful when iterating is xreadlines. For more information, see the section “Iterating Over File Contents,” later in this chapter. The method writelines is the opposite of readlines: Give it a list (or, in fact, any sequence or iterable object) of strings, and it writes all the strings to the file (or stream). Note that newlines are not added: you have to add those yourself. Also, there is no writeline method because you can just use write. ■Note On platforms that use other line separators, substitute “carriage return” (Mac) or “carriage return and newline” (Windows) for “newline.” Closing Your Files You should remember to close your files by calling their close method. Usually, a file object is closed automatically when you quit your program (and possibly before that), and not closing files you have been reading from isn’t really that important (although it can’t hurt, and might help to avoid keeping the file uselessly “locked” against modification in some operating systems and settings). But you should always close a file you have written to because Python may buffer (keep stored temporarily somewhere, for efficiency reasons) the data you have written, and if your program crashes for some reason, the data might not be written to the file at all. The safe thing is to close your files after you’re finished with them. If you want to be certain that your file is closed, you should use a try/finally statement with the call to close in the finally clause: # Open your file here try: # Write data to your file finally: file.close() ■Tip After writing something to a file, you usually want the changes to appear in that file, so other programs reading the same file can see the changes. Well, isn’t that what happens, you say. Not necessarily. As mentioned, the data may be buffered (stored temporarily somewhere in memory), and not written until you close the file. If you want to keep working with the file (and not close it) but still want to make sure the file on disk is updated to reflect your changes, call the file object’s flush method. (Note, however, that flush might not allow other programs running at the same time to access the file, due to locking considerations that depend on your operating system and settings. Whenever you can conveniently close the file, that is preferable.)
262 CHAPTER 11 ■ FILES AND STUFF Examples Assume that somefile.txt contains the text in Listing 11-3. What can you do with it? Listing 11-3. A Simple Text File Welcome to this file There is nothing here except This stupid haiku Let’s try the methods you know: read(n): >>> f = open(r'c:\text\somefile.txt') >>> f.read(7) 'Welcome' >>> f.read(4) ' to ' >>> f.close() read(): >>> f = open(r'c:\text\somefile.txt') >>> print f.read() Welcome to this file There is nothing here except This stupid haiku >>> f.close() readline(): >>> f = open(r'c:\text\somefile.txt') >>> for i in range(3): print str(i) + ': ' + f.readline(), 0: Welcome to this file 1: There is nothing here except 2: This stupid haiku >>> f.close() readlines(): >>> import pprint >>> pprint.pprint(open(r'c:\text\somefile.txt').readlines()) ['Welcome to this file\n', 'There is nothing here except\n', 'This stupid haiku'] Note that I relied on the file object being closed automatically in this example.
Page 2 and 3:
Beginning Python From Novice to Pro
Page 4:
For Ranveig
Page 7 and 8:
■CHAPTER 23 Project 4: In the New
Page 9 and 10:
viii ■CONTENTS Strings . . . . .
Page 11 and 12:
x ■CONTENTS ■CHAPTER 5 Conditio
Page 13 and 14:
xii ■CONTENTS ■CHAPTER 8 Except
Page 15 and 16:
xiv ■CONTENTS ■CHAPTER 11 Files
Page 17 and 18:
xvi ■CONTENTS Dynamic Web Pages w
Page 19 and 20:
xviii ■CONTENTS ■CHAPTER 20 Pro
Page 21 and 22:
xx ■CONTENTS Second Implementatio
Page 23 and 24:
xxii ■CONTENTS Preparations . . .
Page 26:
About the Technical Reviewer ■JER
Page 30 and 31:
Introduction A C program is like a
Page 32 and 33:
CHAPTER 1 ■ ■ ■ Instant Hacki
Page 34 and 35:
CHAPTER 1 ■ INSTANT HACKING: THE
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 44 and 45:
Page 46 and 47:
Page 48 and 49:
Page 50 and 51:
Page 52 and 53:
Page 54 and 55:
Page 56 and 57:
Page 58 and 59:
Page 60 and 61:
Page 62 and 63:
CHAPTER 2 ■ ■ ■ Lists and Tup
Page 64 and 65:
CHAPTER 2 ■ LISTS AND TUPLES 33 I
Page 66 and 67:
CHAPTER 2 ■ LISTS AND TUPLES 35 A
Page 68 and 69:
CHAPTER 2 ■ LISTS AND TUPLES 37 >
Page 70 and 71:
CHAPTER 2 ■ LISTS AND TUPLES 39 M
Page 72 and 73:
CHAPTER 2 ■ LISTS AND TUPLES 41 T
Page 74 and 75:
CHAPTER 2 ■ LISTS AND TUPLES 43 L
Page 76 and 77:
CHAPTER 2 ■ LISTS AND TUPLES 45 W
Page 78 and 79:
CHAPTER 2 ■ LISTS AND TUPLES 47
Page 80 and 81:
CHAPTER 2 ■ LISTS AND TUPLES 49 a
Page 82 and 83:
CHAPTER 2 ■ LISTS AND TUPLES 51 S
Page 84 and 85:
CHAPTER 3 ■ ■ ■ Working with
Page 86 and 87:
CHAPTER 3 ■ WORKING WITH STRINGS
Page 88 and 89:
Page 90 and 91:
Page 92 and 93:
Page 94 and 95:
Page 96 and 97:
Page 98 and 99:
CHAPTER 4 ■ ■ ■ Dictionaries:
Page 100 and 101:
CHAPTER 4 ■ DICTIONARIES: WHEN IN
Page 102 and 103:
Page 104 and 105:
Page 106 and 107:
Page 108 and 109:
Page 110:
Page 113 and 114:
82 CHAPTER 5 ■ CONDITIONALS, LOOP
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
100 CHAPTER 5 ■ CONDITIONALS, LOO
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
110 CHAPTER 6 ■ ABSTRACTION But w
Page 143 and 144:
112 CHAPTER 6 ■ ABSTRACTION ■Ti
Page 145 and 146:
114 CHAPTER 6 ■ ABSTRACTION Can I
Page 147 and 148:
116 CHAPTER 6 ■ ABSTRACTION stora
Page 149 and 150:
118 CHAPTER 6 ■ ABSTRACTION 4. Yo
Page 151 and 152:
120 CHAPTER 6 ■ ABSTRACTION The p
Page 153 and 154:
122 CHAPTER 6 ■ ABSTRACTION >>> p
Page 155 and 156:
124 CHAPTER 6 ■ ABSTRACTION Also,
Page 157 and 158:
126 CHAPTER 6 ■ ABSTRACTION Feel
Page 159 and 160:
128 CHAPTER 6 ■ ABSTRACTION ■No
Page 161 and 162:
130 CHAPTER 6 ■ ABSTRACTION So yo
Page 163 and 164:
132 CHAPTER 6 ■ ABSTRACTION numer
Page 165 and 166:
134 CHAPTER 6 ■ ABSTRACTION LAMBD
Page 167 and 168:
136 CHAPTER 6 ■ ABSTRACTION In th
Page 169 and 170:
138 CHAPTER 6 ■ ABSTRACTION Scope
Page 171 and 172:
140 CHAPTER 7 ■ MORE ABSTRACTION
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
160 CHAPTER 8 ■ EXCEPTIONS >>> im
Page 193 and 194:
162 CHAPTER 8 ■ EXCEPTIONS Custom
Page 195 and 196:
164 CHAPTER 8 ■ EXCEPTIONS More T
Page 197 and 198:
166 CHAPTER 8 ■ EXCEPTIONS try: x
Page 199 and 200:
168 CHAPTER 8 ■ EXCEPTIONS Invali
Page 201 and 202:
170 CHAPTER 8 ■ EXCEPTIONS If you
Page 204 and 205:
CHAPTER 9 ■ ■ ■ Magic Methods
Page 206 and 207:
CHAPTER 9 ■ MAGIC METHODS, PROPER
Page 208 and 209:
Page 210 and 211:
Page 212 and 213:
Page 214 and 215:
Page 216 and 217:
Page 218 and 219:
Page 220 and 221:
Page 222 and 223:
Page 224 and 225:
Page 226 and 227:
Page 228 and 229:
Page 230 and 231:
Page 232 and 233:
Page 234 and 235:
CHAPTER 10 ■ ■ ■ Batteries In
Page 236 and 237:
CHAPTER 10 ■ BATTERIES INCLUDED 2
Page 238 and 239:
Page 240 and 241:
Page 242 and 243: CHAPTER 10 ■ BATTERIES INCLUDED 2
Page 284: CHAPTER 10 ■ BATTERIES INCLUDED 2
Page 287 and 288: 256 CHAPTER 11 ■ FILES AND STUFF
Page 291: 260 CHAPTER 11 ■ FILES AND STUFF
Page 301 and 302: 270 CHAPTER 12 ■ GRAPHICAL USER I
Page 316 and 317: CHAPTER 13 ■ ■ ■ Database Sup
Page 318 and 319: CHAPTER 13 ■ DATABASE SUPPORT 287
Page 326: CHAPTER 13 ■ DATABASE SUPPORT 295
Page 329 and 330: 298 CHAPTER 14 ■ NETWORK PROGRAMM
Page 343 and 344:
312 CHAPTER 14 ■ NETWORK PROGRAMM
Page 345 and 346:
314 CHAPTER 15 ■ PYTHON AND THE W
Page 347 and 348:
Page 349 and 350:
Page 351 and 352:
Page 353 and 354:
Page 355 and 356:
Page 357 and 358:
Page 359 and 360:
Page 361 and 362:
Page 363 and 364:
Page 365 and 366:
Page 367 and 368:
Page 369 and 370:
Page 372 and 373:
CHAPTER 16 ■ ■ ■ Testing, 1-2
Page 374 and 375:
CHAPTER 16 ■ TESTING, 1-2-3 343 W
Page 376 and 377:
CHAPTER 16 ■ TESTING, 1-2-3 345 d
Page 378 and 379:
CHAPTER 16 ■ TESTING, 1-2-3 347 u
Page 380 and 381:
CHAPTER 16 ■ TESTING, 1-2-3 349 F
Page 382 and 383:
CHAPTER 16 ■ TESTING, 1-2-3 351 P
Page 384 and 385:
CHAPTER 16 ■ TESTING, 1-2-3 353 "
Page 386:
CHAPTER 16 ■ TESTING, 1-2-3 355 N
Page 389 and 390:
358 CHAPTER 17 ■ EXTENDING PYTHON
Page 391 and 392:
Page 393 and 394:
Page 395 and 396:
Page 397 and 398:
Page 399 and 400:
Page 401 and 402:
Page 404 and 405:
CHAPTER 18 ■ ■ ■ Packaging Yo
Page 406 and 407:
CHAPTER 18 ■ PACKAGING YOUR PROGR
Page 408 and 409:
Page 410 and 411:
Page 412 and 413:
CHAPTER 19 ■ ■ ■ Playful Prog
Page 414 and 415:
CHAPTER 19 ■ PLAYFUL PROGRAMMING
Page 416 and 417:
Page 418 and 419:
Page 420:
Page 423 and 424:
392 CHAPTER 20 ■ PROJECT 1: INSTA
Page 425 and 426:
Page 427 and 428:
Page 429 and 430:
Page 431 and 432:
Page 433 and 434:
Page 435 and 436:
Page 437 and 438:
Page 439 and 440:
Page 442 and 443:
CHAPTER 21 ■ ■ ■ Project 2: P
Page 444 and 445:
CHAPTER 21 ■ PROJECT 2: PAINTING
Page 446 and 447:
Page 448 and 449:
Page 450 and 451:
Page 452 and 453:
CHAPTER 22 ■ ■ ■ Project 3: X
Page 454 and 455:
CHAPTER 22 ■ PROJECT 3: XML FOR A
Page 456 and 457:
Page 458 and 459:
Page 460 and 461:
Page 462 and 463:
Page 464 and 465:
Page 466 and 467:
Page 468:
Page 471 and 472:
440 CHAPTER 23 ■ PROJECT 4: IN TH
Page 473 and 474:
Page 475 and 476:
Page 477 and 478:
Page 479 and 480:
Page 481 and 482:
Page 483 and 484:
Page 486 and 487:
CHAPTER 24 ■ ■ ■ Project 5: A
Page 488 and 489:
CHAPTER 24 ■ PROJECT 5: A VIRTUAL
Page 490 and 491:
Page 492 and 493:
Page 494 and 495:
Page 496 and 497:
Page 498 and 499:
Page 500 and 501:
Page 502 and 503:
Page 504 and 505:
CHAPTER 25 ■ ■ ■ Project 6: R
Page 506 and 507:
CHAPTER 25 ■ PROJECT 6: REMOTE ED
Page 508 and 509:
Page 510 and 511:
Page 512:
Page 515 and 516:
484 CHAPTER 26 ■ PROJECT 7: YOUR
Page 517 and 518:
Page 519 and 520:
Page 521 and 522:
Page 523 and 524:
Page 525 and 526:
Page 527 and 528:
Page 529 and 530:
Page 531 and 532:
500 CHAPTER 27 ■ PROJECT 8: FILE
Page 533 and 534:
Page 535 and 536:
Page 537 and 538:
Page 539 and 540:
Page 541 and 542:
Page 543 and 544:
Page 545 and 546:
Page 547 and 548:
Page 549 and 550:
Page 551 and 552:
Page 553 and 554:
Page 555 and 556:
Page 558 and 559:
CHAPTER 29 ■ ■ ■ Project 10:
Page 560 and 561:
CHAPTER 29 ■ PROJECT 10: DO-IT-YO
Page 562 and 563:
Page 564 and 565:
Page 566 and 567:
Page 568 and 569:
Page 570 and 571:
Page 572 and 573:
Page 574 and 575:
Page 576 and 577:
Page 578 and 579:
APPENDIX A ■ ■ ■ The Short Ve
Page 580 and 581:
APPENDIX A ■ THE SHORT VERSION 54
Page 582 and 583:
Page 584 and 585:
Page 586:
Page 589 and 590:
558 APPENDIX B ■ PYTHON REFERENCE
Page 591 and 592:
Page 593 and 594:
Page 595 and 596:
Page 597 and 598:
Page 599 and 600:
Page 601 and 602:
Page 603 and 604:
572 APPENDIX C ■ ONLINE RESOURCES
Page 606 and 607:
Index ■Symbols - operator 558 !=
Page 608 and 609:
■INDEX 577 assertEqual method Tes
Page 610 and 611:
■INDEX 579 cmd module 252, 501 Cm
Page 612 and 613:
■INDEX 581 get method 74-75 has_k
Page 614 and 615:
■INDEX 583 ■F Factory class twi
Page 616 and 617:
■INDEX 585 finding conflicts 197
Page 618 and 619:
■INDEX 587 initialization 38 nami
Page 620 and 621:
■INDEX 589 localtime function tim
Page 622 and 623:
■INDEX 591 nesting blocks 88 Netw
Page 624 and 625:
■INDEX 593 playful programming 38
Page 626 and 627:
■INDEX 595 Python C API 365 hand-
Page 628 and 629:
■INDEX 597 ■S safe_substitute m
Page 630 and 631:
■INDEX 599 split function re modu
Page 632 and 633:
■INDEX 601 TestCase class methods
Page 634 and 635:
■INDEX 603 further exploration 47
Page 641:
forums.apress.com FOR PROFESSIONALS
show all

Beginning Python - From Novice to Professional

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

Delete template?

Save as template?