Learning Python, 4th Edition

www.it-ebooks.info interception of built-in attributes, 966– overloading class creation calls with 973 metaclasses, 1066Manager class, 643, 653 declaration, 1062manager functions, 1054 issues around use, 1052manual iteration, 354 potential roles, 1052manynames.py, 694 metafunctions, 804map function, 201, 346, 479 metaprograms, 591–594 method call expression, 173 lambda expressions and, 480 methods, 82, 84, 203, 638, 650, 684–686 list comprehensions and, 491 augmenting methods, 654 list comprehensions, versus, 486 bound and unbound methods, 750–756map iterator, 368 bound methods, 728matching algorithm, 1042 calls to methods, 685–686math module, 79 class methods, 686 example functions, 125 coding methods, 649mathematical functions, 108 comparison methods, 728max and min functions, 364 destructor method, 732mergdexc.py, 846 example, 685metaclass model, 1058–1062, 1058 static methods, 686, 795 (see also metaclasses) class statement protocol, 1061 (see also static methods) classes are instances of type, 1058 superclass constructors, calling, 686 metaclasses are subclasses of type, 1061 min and max functions, 125metaclasses, 781, 794, 807, 1051–1056, 1058 mins.py, 454 (see also metaclass model) mix-in classes, 757 adding methods to classes example, 1070– coding, 757–767 1076 instance attributes, listing, 758 manual augmentation, 1070 listing inherited attributes, 761 metaclass-based augmentation, 1071 listing object attributes in class trees, applying decorators to methods example, 763 1076–1083 module packages, 561 manual tracing, 1076 tracing with metaclasses and decorators, package imports, 561–569 import example, 564–566 1077 justification, 566–569 with any decorators, 1079 packages and search path settings, 562 class decorators, compared to, 1073–1076, __inti__.py, 563 1080 package relative imports (see package decorator-based augmentation, 1073 relative imports) managing instances instead of classes, modules, 42, 51, 75, 529 1074 as extension for import and from, 591 class decorators, compared with, 1056 attributes, 53, 531, 543 coding, 1063–1069 classes, as attributes of, 631 classes, versus, 703 basic metaclass, 1064 creating, 543 customizing construction and data hiding in, 583 design concepts, 598 initialization, 1065 exec, running module files with, 57 factory functions, using, 1066 from statement, 545 instances versus inheritance, 1068 future language features, enabling, 584 overloading class creation calls with global scope, 408 classes, 10671150 | Index

www.it-ebooks.info gotchas, 599–604 multiway branching, 312 from imports and reload, 601 mutable objects, 197, 649 from statement, 600 mutables from statement and variables, 601 recursive import failures, 603 in assignments, 388 statement order in top-level code, 599 mybooks.xml, 934 mydir.py, 592 import statement, 544 myfile.py, 53 importing N byte code compilation if required, 534 running, 535 name attribute, 102 importing by name string, 594 name mangling, 747–750 importing of modules, 533–535 namespace objects, 646 locating, 534 namespaces, 53, 55, 407, 529, 615, 693–701 imports and reloads, 51–57 metaprograms, 591–594 attribute names, 693 mixed-usage modes, 585–589 name assignment, 694–696 module extensions, 544 namespace dictionaries, 696–699 module namespaces, 550–554 namespace links, 699 attribute name qualification, 552 simple names, 693 generation from files, 550 negative offsets, 165 imports versus scopes, 552 nested scopes, 419–425 namespace nesting, 553 abitrary nesting, 424 module search path, 56, 534, 535–541 examples, 419 advanced module selection concepts, factory functions, 420 lambdas and, 422 540 nester.py, 812 module file selection, 539 .NET and IronPython, 30 search path configuration, 537 NetBeans, 63 search path variations, 538 “new-style” classes, 777–794 sys.path list, 538 changes, 778–787 third-party extensions, 540 class extensions, 788–795 module search path, changing, 590 namespaces, 55, 529 class properties, 792–794 naming conventions, 644 instance slots, 788–791 naming of, 543 metaclasses, 794 program structure and, 530 multiple __slot__ lists in superclasses, reloading modules, 554–558 example, 556 790 roles of, 530 slots and generic code, 788 scope, 550 __getattribute__ method, 794 standard library, 533 diamond inheritance change, 783–787 transitive module reloads, 595–598 example, 784 __name__ attribute, 585–589 explicit conflict resolution, 785 command-line arguments with, 587 scope of search order, 787 unit tests, 586 type model changes, 779–783Monty Python’s Flying Circus, 17 object type objects, 782multiline statements, 317 type testing implications, 781multiple inheritance, 617, 756–767 next function, 354 diamond pattern inheritance trees, 783 __next__ method, 352 mix-in classes (see mix-in classes) non-ASCII text, coding, encoding and decoding, 905–906 None object, 247 Index | 1151

www.it-ebooks.infononlocal statement, 409, 425–432 object-oriented programming, 13 absence from Python 2.6, 263 object-oriented scripting language, 5 basics, 425 object.attr expression, 687 examples, 426 object.attribute expression, 613 boundary cases, 428 object.attribute notation, 532 justification for, 429–432 objects, 75, 105, 145 Python 2.6 alternatives, 429 comparisons, equality, and truth, 244normal integers (Python 2.6), 107 compound object types, 241number object type, 78 copying versus referencing, 150number operations, 113–127 databases, storing objects in, 669 dynamic typing and, 144 bitwise operations, 124 iterable objects, 352 comparisons, 116 nonbuilt-in object types, 250 object classifications for built-in types, 240 chained comparisons, 116 references versus copies, 241 complex numbers, 122 truth and falsity, 246 division, 117–121 integer precision, 121 bool type, 248 math module functions, 125 None object, 247 notation, hexadecimal, octal, and binary, type hierarchies, 248 type object type, 250 122 octal numeric literals, 107 numeric display formats, 115 OOP (object-oriented programming), 613– variables and basic expressions, 113–115numeric display formats, 115 621numeric extensions, 140 as exemplified by coding of classes, 658numeric object type, 105–108 attribute inheritance search, 613 built-in numeric tools, 108 class method calls, 616 complexity ranking, 112 classes, 614, 615, 625 expression operators and precedence, 108 numeric literals, 106 class trees, 616–619 operator overloading and polymorphism, customization by inheritance, 629–632 code reuse, 619–621 112 design issues, 737 some noncore types, 127–140 bound and unbound methods, 750–756 composition, 740–745 Booleans, 139 delegation and wrapper classes, 745 decimal type, 127–129 generic object factories, 768 fraction types, 129–133 inheritance, 739 sets, 133–139 multiple inheritance, 756–767numeric precision, setting globally, 128 polymorphism, 738numeric programming, 11 pseudoprivate class attributes, 747–750NumPy numeric programming extension, 7, design patterns, 621 important concepts, 660 11, 140 instances, 614, 615, 625 object.attribute expression, 613O open call, (Python 2.6), 912 open function, 97, 99, 230object embedding, 661 mode string argument, 901object persistence, 669 operator overloading, 240, 613, 633–636, 651–object type categories, 193 653, 652, 705–733 mutable versus immutable types, 194 attribute references, 718–720 shared operation sets, 194object types, 102 built-in object types (see built-in object types)1152 | Index

www.it-ebooks.info attribute privacy, 720 scope, 574 Boolean tests, 730 packages, 561 call expressions, 725–728 parallel traversals, 345 parentheses ( ), 265, 269, 318 function interfaces, 727 common operator overloading methods, functions and, 389 generator expressions and, 497 706 tuples and, 96 comparisons, 728 Parrot project, 33 constructors and expressions, 706 parsing, 165 index iteration, 710 pass statement, 329, 330 indexing and slicing, 708–710 PATH environment variable, 36, 1093 pattern matching, 85 Python 2.6, 709 pdb debugger, 889 iterator objects, 711 PEP (Python Enhancement Proposal) protocol, multiple iterators on one object, 714 12 user defined iterators, 712 Person class, 644 justification, 636 membership, 716 incremental testing, 645 comparisons, Python 2.6, 716 subclassing, 653 object destruction, 732 version portability, 647 overloading methods, 1053 person.py, 644 overloading methods in Python 2.6, 747 Peters, Tim, 1052 overview, 705–707 pickle module, 236, 670, 744 right-side and in-place addition, 723–725 binary data requirement, 933 string representation, 721–723 string serialization (Python 3.0), 932operator precedence, 111 pizzashop.py, 741optimization, 889 polymorphism, 82, 101, 113, 401, 403, 620ORMs (object-relational mappers), 676 dynamic typing and, 153OverflowError class, 865 example, 656 overloading in Python versus otherP languages, 738package imports, 561 pop method, 87, 205, 211 justification, 566–569 portability, 14 import versus from, 569 Portable Python, 1090 root directory, 568 pow function, 125 packages and search path settings, 562 precedencepackage relative imports, 569–581 parentheses and, 111 absolute package paths, versus, 573 precedence rules, 111 basics, 570 print function, 263 examples, 575–581 print operations, 297–307 imports outside packages, 575 imports relative to CWD, 577 print and stdout, 307 imports still relative to CWD, 579 print function (Python 3.0), 298 imports within packages, 576 print statement (Python 2.6), 300 modules, selecting with relative and print stream redirection, 302 absolute imports, 578 version-neutral printing, 306 justification, 572 print statement (Python 2.6), 263 module lookup rules summary, 575 procedure, 396 Python 3.0, 572 profile module, 517, 888 changes, 570 profilers, 888 versus 2.6, 570 program execution, 24–28 Index | 1153

www.it-ebooks.info development implications, 28 configuration, 1093 Python compared to other languages, 27 DOS variables in autoexec.bat, 1095program portability, 4 environment variables, 1093program shipping options, 889 path files, 1096program structure, imports, 531 setting configuration options, 1095program units, 77 Unix/Linux shell variables, 1095programs, 5, 42, 75 Windows environment variable GUI, icons, opening with, 47 1095 launching, 35 Windows registry, 1096 additional launch options, 64 installing, 23 choosing a launch option, 66 Python 2.0 clicking file icons, 47 exec function, 57 string module, 178 from the command line, 43 Python 2.6, xxxii IDLE user interface, 58 input function, 49 backward compatibility to older versions, module imports and reloads, 51, 56 xxxii Unix executable scripts, 46 Windows automatic file extensions, 44 binary and Unicode strings, handling of, running interactively, 35–41 895 experimentation, 38 testing, 39 Booleans, 731 saving in files, 41 iteration method X.next( ), 356 structure, 261, 530–533 nonlocal statement, alternatives to in, 429 Windows, saving under, 45 operator overloading methods, 747property built-in function, 942 Python 3.0 print function, emulating, 457 computed attributes, 945 decorators, 946 using keyword-only arguments, 459 first example, 944 raw_input function, 50proxy classes, 745 reload function, 53pseudoprivate attributes, justification, 748 string object types, 157pseudoprivate names, 747 unicode and str operation sets, 911PSF (Python Software Foundation), 13 “new-style” and “classic” classes, 777Psyco just-in-time compiler, 30, 889 Python 3.0, xxxii.pth file extension, 1096 built-in attributes, 662.pth path file directories, 537 compared 2.x versions, xxxvPVM (Python Virtual Machine), 27 comparisons and sorts, 204.py file extension, 25, 43, 543 dictionary changes, 217py2exe, 32, 889 dictionary comparisons, 246.pyc file extension, 26, 534 extended sequence unpacking, 281, 284PyChecker, PyLint, and PyUnit, 887PyDev, 63 in for loops, 338PyDoc, 84, 380–385, 887 function annotations, 472 help function, 380 incompatibility with older versions, xxxii HTML reports, 383 input function, 50PyInstaller, 32, 889 new iterables, 366–371PyPy project, 33 “new-style” classes, 777Python older version tools removed from, xxxvi command-line options, 1097–1098 special character coding, 908 string object types, 157 string type, changes in, 896 text and binary files, 233 Unicode and binary data support, 895 unsupported raise syntax, 850 Python interpreter, 231154 | Index

www.it-ebooks.info installing, 1089 Chapter 9: Tuples, Files, and Everything on Linux, 1091 Else, 253 on PDAs, 1092 on Unix, 1091 Chapter 10: Introducing Python Statements, on Windows, 1091 276 on Windows Vista, 1092 Chapter 11: Assignments, Expressions, and website downloads link, 1090 Prints, 308Python programming language, xxxi Chapter 12: if Tests and Syntax Rules, 324 advantages of, 3–5 Chapter 13: while and for Loops, 349 common coding gotchas, 387 Chapter 14: Iterations and compared to other languages, 17 developer productivity and, 5 Comprehensions, Part 1, 372 development tools, 886 Chapter 15: The Documentation Interlude, documentation (see documentation) execution speed, 7 389 iteration protocol, 493 Chapter 16: Function Basics, 405 manuals and resources, 1098 Chapter 17: Scopes, 432 old and new versions, xxxii Chapter 18: Arguments, 461 Perl, compared to, 20 Chapter 19: Advanced Function Topics, portability, 14 primary implementations of, 29 483 so-called “optional” features, 1082 Chapter 20: Iterations and statically-typed languages, compared to, Comprehensions, Part 2, 523 401 Chapter 21: Modules, the Big Picture, 541 string model, 897–902 Chapter 22: Module Coding Basics, 558 support, 12 Chapter 23: Module Packages, 582 technical strengths, 13–17 Chapter 24: Advanced Module Topics, 604 user base, 7 Chapter 25: OOP: The Big Picture, 622 uses for, 9–12 Chapter 26: Class Coding Basics, 641PYTHONPATH, 1094 Chapter 27: A More Realistic Example,PYTHONPATH directories, 536PYTHONSTARTUP, 1094 677PythonWin, 63, 1090 Chapter 28: Class Coding Details, 703PyWin32, 1090 Chapter 29: Operator Overloading, 734 Chapter 30: Designing with Classes, 770Q Chapter 31: Advanced Class Topics, 815 Chapter 32: Exception Basics, 833quizzes, xliii Chapter 33: Exception Coding Details, 856 Chapter 1: A Python Q&A Session, 19 Chapter 34: Exception Objects, 870 Chapter 2: How Python Runs Programs, Chapter 35: Designing with Exceptions, 34 Chapter 3: How You Run Programs, 68 891 Chapter 4: Introducing Python Object Chapter 36: Unicode and Byte Strings, 937 Types, 103 Chapter 37: Managed Attributes, 979 Chapter 5: Numeric Types, 141 Chapter 38: Decorators, 1047 Chapter 6: The Dynamic Typing Interlude, Chapter 39: Metaclasses, 1084 153 quotes Chapter 7: Strings, 195 escaping, 158 Chapter 8: Lists and Dictionaries, 223 strings and, 158 triple quotes, 162 R raise statement, 829, 848–850 from clause Python 3.0 exception chaining, 849 Index | 1155

www.it-ebooks.info nonerror conditions, signaling with, 878 rstrip method, 235random module, 79, 127range S versus for loops, 388 SAX parsing, 935range function, 342 scientific programming, 11range iterator, 367 ScientificPython programming extensions, 12 SciPy programming extensions, 12, 140 support for multiple iterators, 369 scopes, 407–414rapid prototyping, 11rational number objects, 129 basics, 407raw string literals, 85 built-in scope, 412raw strings, 161 defaults with loop variables, versus, 423raw_input function (Python 2.x), 50 example, 411re (regular expression) module, 85 global statements, 408 module files and, 416 string handling in Python 3.0, 929 name resolution and the LEGB rule, 410read method, 233 namespaces, 407readline method, 98, 232 nested functions and, 419–425recursive functions, 465–469 nonlocal, 408 rules, 408 arbitrary structures, handling, 468 script0.py, 24 coding alternatives, 466 script1.py, 42 direct or indirect, 467 running with an import, 51 loop statements, versus, 467 scripts, 5, 42 summation, 465 search tables (see dictionaries)recursive imports, 603 self argument, 685reduce, 363 semicolon (;), 265reduce function, 481 send method, 496reference counters, 147 sequence assignment statements, 280references, 145 sequence assignments, 281–284 copies of objects, versus, 241 sequence operations, 80 shared references, 148–152 sequences, 80 set comprehensions, 507 equality, 151 set numeric type, 133–139 in-place changes, 149 dictionaries, compared to, 135relative imports, 561 immutable constraints and frozen sets, 136reload function, 52, 554–558 Python 2.6, 133 example, 556 Python 3.0, 135 from imports and, 601 set comprehensions in Python 3.0, 137 interactive testing, 602 set object type, 99 import and from, contrasted with, 555 setsubclass.py, 776 transitive module reloads, 595–598 shared references, 148–152 usage notes, 56 equality, 151 version 3.0 requirements, 53 in-place changes, 149reloadall.py, 596 Shedskin C++ translator, 31, 889remove method, 87, 206 shelve module, 670–675, 744repetition, 81 advantages and disadvantages, 673replace method, 83 database client, 672repr function, 79 database files, 672 str, compared to, 116 object storage in shelve databases, 671return statement, 397, 398, 404reverse method, 87, 205round function, 1261156 | Index

www.it-ebooks.info shelves and dictionaries, 670 colon (:), 264 updating a shelve’s objects, 674 indentation, 266simple functions, 796 interactive loops, 271–276single quotes (') and strings, 158 semicolons, 269site module, 537 statement separators, 269slice assignment in lists, 202 static methods, 686, 795–801slice objects, 168 alternatives to, 798slicing, 81, 165, 166 coding with decorator syntax, 804 example, 168 counting instances, 800 extended slicing, 167 Python 2.6 and 3.0, 796 loops, usage in, 343 using, 799software components, 653 staticmethod function, 799sort method, 87, 203, 388, 454 steps, 167sorted function, 93, 363 StopIteration exception, 352sorts in Python 3.0, 204 str, 79, 157, 169source code, 26 repr, compared to, 116source file character set encoding declarations, str object type data encoding in, 901 912 str string type, 899spaces, 314 Python 2.6 operation set, 911special characters, 897 Python 3.0 compared to 2.x, 899split method, 235 Unicode and, 85square brackets [ ], 78, 108, 269 stream processors, 742 stream redirection, 44 dictionaries and, 209 strides, 167 list comprehensions and, 359, 486, 504 string exceptions, 859 lists and, 89, 199 deprecation of, 858square roots, 126 string formatting, 179–183stack trace, 828, 840 advanced expressions, 181Stackless Python, 33 dictionary-based formatting expressions,standard library, 4, 533 library directories, 537 182standard manual set, 386 string formatting type codes, 181standard output stream (stdout), 297 string formatting method calls, 183–193state information, 102, 644 format method, 184–193 state retention, 429–432, 727, 997–1000state with classes, 430 % formatting expression, compared to,statements, 75, 261–276 187 assignment statements (see assignment justification for, 190 statements) keys, attributes, and offsets, 184 compound statements, 264 string methods, 172–179 differences from other C-like languages, additional examples, 177 changing strings example, 174 265 parsing text example, 176 end-of-line, 265 Python 2.x string module, 178 expression statements, 295 string method calls to format method, 185 string method calls, Python 3.0, 173 in-place changes, 296 string object type, 80–86, 155–163 indentation syntax, 266 coding special characters, 85 multiline statements, 317 pattern matching, 85 Python 3.0 statement set, 262 raw string literals, 85 syntax, 264 block rule special case, 270 Index | 1157

www.it-ebooks.info sequence operations and, 80 struct binary data module (Python 3.0), string literals, 157–163 930 common literals and operations, 155 text and binary files, 920 escape sequences, 158–161 BOM in Python 3.0, 926 raw strings and escapes, 161 file modes in Python 3.0, 921 single and double quoted strings, 158 type and content mismatches, 923 string backslash characters, 159 Unicode in Python 2.6, 928 triple quotes, 162 version 3.0 changes, 896 type conversions, 903 versions 2.6 and 3.0 string types, 157 Unicode files, using, 924string operations, 163–172 basic operations, 164 reading and writing in Python 3.0, 924 changing strings, 171 unicode strings, coding, 904 indexing, 165, 166 Unicode strings, Python 2.6 coding, 910 slicing, 165, 166 XML parsing tools, 934 extended slicing, 167 strong typing, 78 string conversions, 169 struct module string handling, Python 3.0, character code conversions, 170strings, 897 930 16- and 32-bit Unicode values, coding of, subclasses, 614, 629, 653–658 907 coding, 653–658 ASCII text, coding, 905 augmenting methods, 654–656 bytearray objects, using, 917–920 inheritance, customization, and bytes objects (Python 3.0), 913–917 extension, 657 OOP, as illustration of, 658 method calls, 913 polymorphism, 656 sequence operations, 914 bytes string type sum function, 125 making bytes objects, 915 Super class, 689 character encoding schemes and, 897 superclasses, 614, 629 encoding conversions, 909 escape sequence coding by type, 908 abstract superclasses, 690–693 examples of usage (Python 3.0), 902–904 syntax rules, 264–271, 314–319 literals and basic properties, 902 mixing string types, 916 indentation, 315 mutability or immutability of string types, multiline statements, 317 open syntactic pairs rule, 318 903 sys.exc_info, 880–882 non-ASCII text, coding, 905 sys.exit(statuscode) call, 883 non-ASCII text, encoding and decoding, sys.getdefaultencoding function, 896 sys.modules table, 534 906 sys.path list, 536, 538, 590 pickle object serialization module (Python system namespace partitioning and modules, 3.0), 932 530 Python 3.0 string types, usage, 920 systems programming, 9 re pattern matching module (Python 3.0), T 929 source file character set encoding termination actions, 830 testdriver function, 880 declarations, 912 tester, 426 string methods, 82 testing of code, 645 string types, 899 testmixin.py, 759 testprint30.py, 458 text files, 98, 233, 901, 920 in Python 3.0, 9211158 | Index