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1 Python 2.3 Quick Reference 2 3 4 25 Jan 2003 upgraded by Raymond Hettinger for Python 2.3 5 16 May 2001 upgraded by Richard Gruet and Simon Brunning for Python 2.0 6 2000/07/18 upgraded by Richard Gruet, rgruet@intraware.com for Python 1.5.2 7from V1.3 ref 81995/10/30, by Chris Hoffmann, choffman@vicorp.com 9 10Based on: 11 Python Bestiary, Author: Ken Manheimer, ken.manheimer@nist.gov 12 Python manuals, Authors: Guido van Rossum and Fred Drake 13 What's new in Python 2.0, Authors: A.M. Kuchling and Moshe Zadka 14 python-mode.el, Author: Tim Peters, tim_one@email.msn.com 15 16 and the readers of comp.lang.python 17 18Python's nest: http://www.python.org Developement: http:// 19python.sourceforge.net/ ActivePython : http://www.ActiveState.com/ASPN/ 20Python/ 21newsgroup: comp.lang.python Help desk: help@python.org 22Resources: http://starship.python.net/ 23 http://www.vex.net/parnassus/ 24 http://aspn.activestate.com/ASPN/Cookbook/Python 25FAQ: http://www.python.org/cgi-bin/faqw.py 26Full documentation: http://www.python.org/doc/ 27Excellent reference books: 28 Python Essential Reference by David Beazley (New Riders) 29 Python Pocket Reference by Mark Lutz (O'Reilly) 30 31 32Invocation Options 33 34python [-diOStuUvxX?] [-c command | script | - ] [args] 35 36 Invocation Options 37Option Effect 38-c cmd program passed in as string (terminates option list) 39-d Outputs parser debugging information (also PYTHONDEBUG=x) 40-E ignore environment variables (such as PYTHONPATH) 41-h print this help message and exit 42-i Inspect interactively after running script (also PYTHONINSPECT=x) and 43 force prompts, even if stdin appears not to be a terminal 44-m mod run library module as a script (terminates option list 45-O optimize generated bytecode (a tad; also PYTHONOPTIMIZE=x) 46-OO remove doc-strings in addition to the -O optimizations 47-Q arg division options: -Qold (default), -Qwarn, -Qwarnall, -Qnew 48-S Don't perform 'import site' on initialization 49-t Issue warnings about inconsistent tab usage (-tt: issue errors) 50-u Unbuffered binary stdout and stderr (also PYTHONUNBUFFERED=x). 51-v Verbose (trace import statements) (also PYTHONVERBOSE=x) 52-W arg : warning control (arg is action:message:category:module:lineno) 53-x Skip first line of source, allowing use of non-unix Forms of #!cmd 54-? Help! 55-3 warn about Python 3.x incompatibilities 56-c Specify the command to execute (see next section). This terminates the 57command option list (following options are passed as arguments to the command). 58 the name of a python file (.py) to execute read from stdin. 59script Anything afterward is passed as options to python script or command, 60 not interpreted as an option to interpreter itself. 61args passed to script or command (in sys.argv[1:]) 62 If no script or command, Python enters interactive mode. 63 64 * Available IDEs in std distrib: IDLE (tkinter based, portable), Pythonwin 65 (Windows). 66 67 68 69Environment variables 70 71 Environment variables 72 Variable Effect 73PYTHONHOME Alternate prefix directory (or prefix;exec_prefix). The 74 default module search path uses prefix/lib 75 Augments the default search path for module files. The format 76 is the same as the shell's $PATH: one or more directory 77 pathnames separated by ':' or ';' without spaces around 78 (semi-)colons! 79PYTHONPATH On Windows first search for Registry key HKEY_LOCAL_MACHINE\ 80 Software\Python\PythonCore\x.y\PythonPath (default value). You 81 may also define a key named after your application with a 82 default string value giving the root directory path of your 83 app. 84 If this is the name of a readable file, the Python commands in 85PYTHONSTARTUP that file are executed before the first prompt is displayed in 86 interactive mode (no default). 87PYTHONDEBUG If non-empty, same as -d option 88PYTHONINSPECT If non-empty, same as -i option 89PYTHONSUPPRESS If non-empty, same as -s option 90PYTHONUNBUFFERED If non-empty, same as -u option 91PYTHONVERBOSE If non-empty, same as -v option 92PYTHONCASEOK If non-empty, ignore case in file/module names (imports) 93 94 95 96 97Notable lexical entities 98 99Keywords 100 101 and del for is raise 102 assert elif from lambda return 103 break else global not try 104 class except if or while 105 continue exec import pass yield 106 def finally in print 107 108 * (list of keywords in std module: keyword) 109 * Illegitimate Tokens (only valid in strings): @ $ ? 110 * A statement must all be on a single line. To break a statement over 111 multiple lines use "\", as with the C preprocessor. 112 Exception: can always break when inside any (), [], or {} pair, or in 113 triple-quoted strings. 114 * More than one statement can appear on a line if they are separated with 115 semicolons (";"). 116 * Comments start with "#" and continue to end of line. 117 118Identifiers 119 120 (letter | "_") (letter | digit | "_")* 121 122 * Python identifiers keywords, attributes, etc. are case-sensitive. 123 * Special forms: _ident (not imported by 'from module import *'); __ident__ 124 (system defined name); 125 __ident (class-private name mangling) 126 127Strings 128 129 "a string enclosed by double quotes" 130 'another string delimited by single quotes and with a " inside' 131 '''a string containing embedded newlines and quote (') marks, can be 132 delimited with triple quotes.''' 133 """ may also use 3- double quotes as delimiters """ 134 u'a unicode string' U"Another unicode string" 135 r'a raw string where \ are kept (literalized): handy for regular 136 expressions and windows paths!' 137 R"another raw string" -- raw strings cannot end with a \ 138 ur'a unicode raw string' UR"another raw unicode" 139 140 Use \ at end of line to continue a string on next line. 141 adjacent strings are concatened, e.g. 'Monty' ' Python' is the same as 142 'Monty Python'. 143 u'hello' + ' world' --> u'hello world' (coerced to unicode) 144 145 String Literal Escapes 146 147 \newline Ignored (escape newline) 148 \\ Backslash (\) \e Escape (ESC) \v Vertical Tab (VT) 149 \' Single quote (') \f Formfeed (FF) \OOO char with octal value OOO 150 \" Double quote (") \n Linefeed (LF) 151 \a Bell (BEL) \r Carriage Return (CR) \xHH char with hex value HH 152 \b Backspace (BS) \t Horizontal Tab (TAB) 153 \uHHHH unicode char with hex value HHHH, can only be used in unicode string 154 \UHHHHHHHH unicode char with hex value HHHHHHHH, can only be used in unicode string 155 \AnyOtherChar is left as-is 156 157 * NUL byte (\000) is NOT an end-of-string marker; NULs may be embedded in 158 strings. 159 * Strings (and tuples) are immutable: they cannot be modified. 160 161Numbers 162 163 Decimal integer: 1234, 1234567890546378940L (or l) 164 Octal integer: 0177, 0177777777777777777 (begin with a 0) 165 Hex integer: 0xFF, 0XFFFFffffFFFFFFFFFF (begin with 0x or 0X) 166 Long integer (unlimited precision): 1234567890123456 167 Float (double precision): 3.14e-10, .001, 10., 1E3 168 Complex: 1J, 2+3J, 4+5j (ends with J or j, + separates (float) real and 169 imaginary parts) 170 171Sequences 172 173 * String of length 0, 1, 2 (see above) 174 '', '1', "12", 'hello\n' 175 * Tuple of length 0, 1, 2, etc: 176 () (1,) (1,2) # parentheses are optional if len > 0 177 * List of length 0, 1, 2, etc: 178 [] [1] [1,2] 179 180Indexing is 0-based. Negative indices (usually) mean count backwards from end 181of sequence. 182 183Sequence slicing [starting-at-index : but-less-than-index]. Start defaults to 184'0'; End defaults to 'sequence-length'. 185 186a = (0,1,2,3,4,5,6,7) 187 a[3] ==> 3 188 a[-1] ==> 7 189 a[2:4] ==> (2, 3) 190 a[1:] ==> (1, 2, 3, 4, 5, 6, 7) 191 a[:3] ==> (0, 1, 2) 192 a[:] ==> (0,1,2,3,4,5,6,7) # makes a copy of the sequence. 193 194Dictionaries (Mappings) 195 196 {} # Zero length empty dictionary 197 {1 : 'first'} # Dictionary with one (key, value) pair 198 {1 : 'first', 'next': 'second'} 199 dict([('one',1),('two',2)]) # Construct a dict from an item list 200 dict('one'=1, 'two'=2) # Construct a dict using keyword args 201 dict.fromkeys(['one', 'keys']) # Construct a dict from a sequence 202 203Operators and their evaluation order 204 205 Operators and their evaluation order 206Highest Operator Comment 207 (...) [...] {...} `...` Tuple, list & dict. creation; string 208 conv. 209 s[i] s[i:j] s.attr f(...) indexing & slicing; attributes, fct 210 calls 211 +x, -x, ~x Unary operators 212 x**y Power 213 x*y x/y x%y x//y mult, division, modulo, floor division 214 x+y x-y addition, subtraction 215 x<<y x>>y Bit shifting 216 x&y Bitwise and 217 x^y Bitwise exclusive or 218 x|y Bitwise or 219 x<y x<=y x>y x>=y x==y x!=y Comparison, 220 x<>y identity, 221 x is y x is not y membership 222 x in s x not in s 223 not x boolean negation 224 x and y boolean and 225 x or y boolean or 226Lowest lambda args: expr anonymous function 227 228Alternate names are defined in module operator (e.g. __add__ and add for +) 229Most operators are overridable. 230 231Many binary operators also support augmented assignment: 232 x += 1 # Same as x = x + 1 233 234 235Basic Types and Their Operations 236 237Comparisons (defined between *any* types) 238 239 Comparisons 240Comparison Meaning Notes 241< strictly less than (1) 242<= less than or equal to 243> strictly greater than 244>= greater than or equal to 245== equal to 246!= or <> not equal to 247is object identity (2) 248is not negated object identity (2) 249 250Notes : 251 Comparison behavior can be overridden for a given class by defining special 252method __cmp__. 253 The above comparisons return True or False which are of type bool 254(a subclass of int) and behave exactly as 1 or 0 except for their type and 255that they print as True or False instead of 1 or 0. 256 (1) X < Y < Z < W has expected meaning, unlike C 257 (2) Compare object identities (i.e. id(object)), not object values. 258 259Boolean values and operators 260 261 Boolean values and operators 262 Value or Operator Returns Notes 263None, numeric zeros, empty sequences and False 264mappings 265all other values True 266not x True if x is False, else 267 True 268x or y if x is False then y, else (1) 269 x 270x and y if x is False then x, else (1) 271 y 272 273Notes : 274 Truth testing behavior can be overridden for a given class by defining 275special method __nonzero__. 276 (1) Evaluate second arg only if necessary to determine outcome. 277 278None 279 280 None is used as default return value on functions. Built-in single object 281 with type NoneType. 282 Input that evaluates to None does not print when running Python 283 interactively. 284 285Numeric types 286 287Floats, integers and long integers. 288 289 Floats are implemented with C doubles. 290 Integers are implemented with C longs. 291 Long integers have unlimited size (only limit is system resources) 292 293Operators on all numeric types 294 295 Operators on all numeric types 296 Operation Result 297abs(x) the absolute value of x 298int(x) x converted to integer 299long(x) x converted to long integer 300float(x) x converted to floating point 301-x x negated 302+x x unchanged 303x + y the sum of x and y 304x - y difference of x and y 305x * y product of x and y 306x / y quotient of x and y 307x % y remainder of x / y 308divmod(x, y) the tuple (x/y, x%y) 309x ** y x to the power y (the same as pow(x, y)) 310 311Bit operators on integers and long integers 312 313 Bit operators 314Operation >Result 315~x the bits of x inverted 316x ^ y bitwise exclusive or of x and y 317x & y bitwise and of x and y 318x | y bitwise or of x and y 319x << n x shifted left by n bits 320x >> n x shifted right by n bits 321 322Complex Numbers 323 324 * represented as a pair of machine-level double precision floating point 325 numbers. 326 * The real and imaginary value of a complex number z can be retrieved through 327 the attributes z.real and z.imag. 328 329Numeric exceptions 330 331TypeError 332 raised on application of arithmetic operation to non-number 333OverflowError 334 numeric bounds exceeded 335ZeroDivisionError 336 raised when zero second argument of div or modulo op 337FloatingPointError 338 raised when a floating point operation fails 339 340Operations on all sequence types (lists, tuples, strings) 341 342 Operations on all sequence types 343Operation Result Notes 344x in s True if an item of s is equal to x, else False 345x not in s False if an item of s is equal to x, else True 346for x in s: loops over the sequence 347s + t the concatenation of s and t 348s * n, n*s n copies of s concatenated 349s[i] i'th item of s, origin 0 (1) 350s[i:j] slice of s from i (included) to j (excluded) (1), (2) 351len(s) length of s 352min(s) smallest item of s 353max(s) largest item of (s) 354iter(s) returns an iterator over s. iterators define __iter__ and next() 355 356Notes : 357 (1) if i or j is negative, the index is relative to the end of the string, 358ie len(s)+ i or len(s)+j is 359 substituted. But note that -0 is still 0. 360 (2) The slice of s from i to j is defined as the sequence of items with 361index k such that i <= k < j. 362 If i or j is greater than len(s), use len(s). If i is omitted, use 363len(s). If i is greater than or 364 equal to j, the slice is empty. 365 366Operations on mutable (=modifiable) sequences (lists) 367 368 Operations on mutable sequences 369 Operation Result Notes 370s[i] =x item i of s is replaced by x 371s[i:j] = t slice of s from i to j is replaced by t 372del s[i:j] same as s[i:j] = [] 373s.append(x) same as s[len(s) : len(s)] = [x] 374s.count(x) return number of i's for which s[i] == x 375s.extend(x) same as s[len(s):len(s)]= x 376s.index(x) return smallest i such that s[i] == x (1) 377s.insert(i, x) same as s[i:i] = [x] if i >= 0 378s.pop([i]) same as x = s[i]; del s[i]; return x (4) 379s.remove(x) same as del s[s.index(x)] (1) 380s.reverse() reverse the items of s in place (3) 381s.sort([cmpFct]) sort the items of s in place (2), (3) 382 383Notes : 384 (1) raise a ValueError exception when x is not found in s (i.e. out of 385range). 386 (2) The sort() method takes an optional argument specifying a comparison 387fct of 2 arguments (list items) which should 388 return -1, 0, or 1 depending on whether the 1st argument is 389considered smaller than, equal to, or larger than the 2nd 390 argument. Note that this slows the sorting process down considerably. 391 (3) The sort() and reverse() methods modify the list in place for economy 392of space when sorting or reversing a large list. 393 They don't return the sorted or reversed list to remind you of this 394side effect. 395 (4) [New 1.5.2] The optional argument i defaults to -1, so that by default the last 396item is removed and returned. 397 398 399 400Operations on mappings (dictionaries) 401 402 Operations on mappings 403 Operation Result Notes 404len(d) the number of items in d 405d[k] the item of d with key k (1) 406d[k] = x set d[k] to x 407del d[k] remove d[k] from d (1) 408d.clear() remove all items from d 409d.copy() a shallow copy of d 410d.get(k,defaultval) the item of d with key k (4) 411d.has_key(k) True if d has key k, else False 412d.items() a copy of d's list of (key, item) pairs (2) 413d.iteritems() an iterator over (key, value) pairs (7) 414d.iterkeys() an iterator over the keys of d (7) 415d.itervalues() an iterator over the values of d (7) 416d.keys() a copy of d's list of keys (2) 417d1.update(d2) for k, v in d2.items(): d1[k] = v (3) 418d.values() a copy of d's list of values (2) 419d.pop(k) remove d[k] and return its value 420d.popitem() remove and return an arbitrary (6) 421 (key, item) pair 422d.setdefault(k,defaultval) the item of d with key k (5) 423 424 Notes : 425 TypeError is raised if key is not acceptable 426 (1) KeyError is raised if key k is not in the map 427 (2) Keys and values are listed in random order 428 (3) d2 must be of the same type as d1 429 (4) Never raises an exception if k is not in the map, instead it returns 430 defaultVal. 431 defaultVal is optional, when not provided and k is not in the map, 432 None is returned. 433 (5) Never raises an exception if k is not in the map, instead it returns 434 defaultVal, and adds k to map with value defaultVal. defaultVal is 435 optional. When not provided and k is not in the map, None is returned and 436 added to map. 437 (6) Raises a KeyError if the dictionary is emtpy. 438 (7) While iterating over a dictionary, the values may be updated but 439 the keys cannot be changed. 440 441Operations on strings 442 443Note that these string methods largely (but not completely) supersede the 444functions available in the string module. 445 446 447 Operations on strings 448 Operation Result Notes 449s.capitalize() return a copy of s with only its first character 450 capitalized. 451s.center(width) return a copy of s centered in a string of length width (1) 452 . 453s.count(sub[ return the number of occurrences of substring sub in (2) 454,start[,end]]) string s. 455s.decode(([ return a decoded version of s. (3) 456 encoding 457 [,errors]]) 458s.encode([ return an encoded version of s. Default encoding is the 459 encoding current default string encoding. (3) 460 [,errors]]) 461s.endswith(suffix return true if s ends with the specified suffix, (2) 462 [,start[,end]]) otherwise return False. 463s.expandtabs([ return a copy of s where all tab characters are (4) 464tabsize]) expanded using spaces. 465s.find(sub[,start return the lowest index in s where substring sub is (2) 466[,end]]) found. Return -1 if sub is not found. 467s.index(sub[ like find(), but raise ValueError when the substring is (2) 468,start[,end]]) not found. 469s.isalnum() return True if all characters in s are alphanumeric, (5) 470 False otherwise. 471s.isalpha() return True if all characters in s are alphabetic, (5) 472 False otherwise. 473s.isdigit() return True if all characters in s are digit (5) 474 characters, False otherwise. 475s.islower() return True if all characters in s are lowercase, False (6) 476 otherwise. 477s.isspace() return True if all characters in s are whitespace (5) 478 characters, False otherwise. 479s.istitle() return True if string s is a titlecased string, False (7) 480 otherwise. 481s.isupper() return True if all characters in s are uppercase, False (6) 482 otherwise. 483s.join(seq) return a concatenation of the strings in the sequence 484 seq, separated by 's's. 485s.ljust(width) return s left justified in a string of length width. (1), 486 (8) 487s.lower() return a copy of s converted to lowercase. 488s.lstrip() return a copy of s with leading whitespace removed. 489s.replace(old, return a copy of s with all occurrences of substring (9) 490new[, maxsplit]) old replaced by new. 491s.rfind(sub[ return the highest index in s where substring sub is (2) 492,start[,end]]) found. Return -1 if sub is not found. 493s.rindex(sub[ like rfind(), but raise ValueError when the substring (2) 494,start[,end]]) is not found. 495s.rjust(width) return s right justified in a string of length width. (1), 496 (8) 497s.rstrip() return a copy of s with trailing whitespace removed. 498s.split([sep[ return a list of the words in s, using sep as the (10) 499,maxsplit]]) delimiter string. 500s.splitlines([ return a list of the lines in s, breaking at line (11) 501keepends]) boundaries. 502s.startswith return true if s starts with the specified prefix, 503(prefix[,start[ otherwise return false. (2) 504,end]]) 505s.strip() return a copy of s with leading and trailing whitespace 506 removed. 507s.swapcase() return a copy of s with uppercase characters converted 508 to lowercase and vice versa. 509 return a titlecased copy of s, i.e. words start with 510s.title() uppercase characters, all remaining cased characters 511 are lowercase. 512s.translate(table return a copy of s mapped through translation table (12) 513[,deletechars]) table. 514s.upper() return a copy of s converted to uppercase. 515s.zfill(width) return a string padded with zeroes on the left side and 516 sliding a minus sign left if necessary. never truncates. 517 518Notes : 519 (1) Padding is done using spaces. 520 (2) If optional argument start is supplied, substring s[start:] is 521processed. If optional arguments start and end are supplied, substring s[start: 522end] is processed. 523 (3) Optional argument errors may be given to set a different error handling 524scheme. The default for errors is 'strict', meaning that encoding errors raise 525a ValueError. Other possible values are 'ignore' and 'replace'. 526 (4) If optional argument tabsize is not given, a tab size of 8 characters 527is assumed. 528 (5) Returns false if string s does not contain at least one character. 529 (6) Returns false if string s does not contain at least one cased 530character. 531 (7) A titlecased string is a string in which uppercase characters may only 532follow uncased characters and lowercase characters only cased ones. 533 (8) s is returned if width is less than len(s). 534 (9) If the optional argument maxsplit is given, only the first maxsplit 535occurrences are replaced. 536 (10) If sep is not specified or None, any whitespace string is a separator. 537If maxsplit is given, at most maxsplit splits are done. 538 (11) Line breaks are not included in the resulting list unless keepends is 539given and true. 540 (12) table must be a string of length 256. All characters occurring in the 541optional argument deletechars are removed prior to translation. 542 543String formatting with the % operator 544 545formatString % args--> evaluates to a string 546 547 * formatString uses C printf format codes : %, c, s, i, d, u, o, x, X, e, E, 548 f, g, G, r (details below). 549 * Width and precision may be a * to specify that an integer argument gives 550 the actual width or precision. 551 * The flag characters -, +, blank, # and 0 are understood. (details below) 552 * %s will convert any type argument to string (uses str() function) 553 * args may be a single arg or a tuple of args 554 555 '%s has %03d quote types.' % ('Python', 2) # => 'Python has 002 quote types.' 556 557 * Right-hand-side can also be a mapping: 558 559 a = '%(lang)s has %(c)03d quote types.' % {'c':2, 'lang':'Python} 560(vars() function very handy to use on right-hand-side.) 561 562 Format codes 563Conversion Meaning 564d Signed integer decimal. 565i Signed integer decimal. 566o Unsigned octal. 567u Unsigned decimal. 568x Unsigned hexadecimal (lowercase). 569X Unsigned hexadecimal (uppercase). 570e Floating point exponential format (lowercase). 571E Floating point exponential format (uppercase). 572f Floating point decimal format. 573F Floating point decimal format. 574g Same as "e" if exponent is greater than -4 or less than precision, 575 "f" otherwise. 576G Same as "E" if exponent is greater than -4 or less than precision, 577 "F" otherwise. 578c Single character (accepts integer or single character string). 579r String (converts any python object using repr()). 580s String (converts any python object using str()). 581% No argument is converted, results in a "%" character in the result. 582 (The complete specification is %%.) 583 584 Conversion flag characters 585Flag Meaning 586# The value conversion will use the ``alternate form''. 5870 The conversion will be zero padded. 588- The converted value is left adjusted (overrides "-"). 589 (a space) A blank should be left before a positive number (or empty 590 string) produced by a signed conversion. 591+ A sign character ("+" or "-") will precede the conversion (overrides a 592 "space" flag). 593 594File Objects 595 596Created with built-in function open; may be created by other modules' functions 597as well. 598 599Operators on file objects 600 601 File operations 602 Operation Result 603f.close() Close file f. 604f.fileno() Get fileno (fd) for file f. 605f.flush() Flush file f's internal buffer. 606f.isatty() True if file f is connected to a tty-like dev, else False. 607f.read([size]) Read at most size bytes from file f and return as a string 608 object. If size omitted, read to EOF. 609f.readline() Read one entire line from file f. 610f.readlines() Read until EOF with readline() and return list of lines read. 611 Set file f's position, like "stdio's fseek()". 612f.seek(offset[, whence == 0 then use absolute indexing. 613whence=0]) whence == 1 then offset relative to current pos. 614 whence == 2 then offset relative to file end. 615f.tell() Return file f's current position (byte offset). 616f.write(str) Write string to file f. 617f.writelines(list Write list of strings to file f. 618) 619 620File Exceptions 621 622 EOFError 623 End-of-file hit when reading (may be raised many times, e.g. if f is a 624 tty). 625 IOError 626 Other I/O-related I/O operation failure. 627 OSError 628 OS system call failed. 629 630 631 Advanced Types 632 633 -See manuals for more details - 634 + Module objects 635 + Class objects 636 + Class instance objects 637 + Type objects (see module: types) 638 + File objects (see above) 639 + Slice objects 640 + XRange objects 641 + Callable types: 642 o User-defined (written in Python): 643 # User-defined Function objects 644 # User-defined Method objects 645 o Built-in (written in C): 646 # Built-in Function objects 647 # Built-in Method objects 648 + Internal Types: 649 o Code objects (byte-compile executable Python code: bytecode) 650 o Frame objects (execution frames) 651 o Traceback objects (stack trace of an exception) 652 653 654 Statements 655 656 pass -- Null statement 657 del name[,name]* -- Unbind name(s) from object. Object will be indirectly 658 (and automatically) deleted only if no longer referenced. 659 print [>> fileobject,] [s1 [, s2 ]* [,] 660 -- Writes to sys.stdout, or to fileobject if supplied. 661 Puts spaces between arguments. Puts newline at end 662 unless statement ends with comma. 663 Print is not required when running interactively, 664 simply typing an expression will print its value, 665 unless the value is None. 666 exec x [in globals [,locals]] 667 -- Executes x in namespaces provided. Defaults 668 to current namespaces. x can be a string, file 669 object or a function object. 670 callable(value,... [id=value], [*args], [**kw]) 671 -- Call function callable with parameters. Parameters can 672 be passed by name or be omitted if function 673 defines default values. E.g. if callable is defined as 674 "def callable(p1=1, p2=2)" 675 "callable()" <=> "callable(1, 2)" 676 "callable(10)" <=> "callable(10, 2)" 677 "callable(p2=99)" <=> "callable(1, 99)" 678 *args is a tuple of positional arguments. 679 **kw is a dictionary of keyword arguments. 680 681 Assignment operators 682 683 Caption 684 Operator Result Notes 685 a = b Basic assignment - assign object b to label a (1) 686 a += b Roughly equivalent to a = a + b (2) 687 a -= b Roughly equivalent to a = a - b (2) 688 a *= b Roughly equivalent to a = a * b (2) 689 a /= b Roughly equivalent to a = a / b (2) 690 a %= b Roughly equivalent to a = a % b (2) 691 a **= b Roughly equivalent to a = a ** b (2) 692 a &= b Roughly equivalent to a = a & b (2) 693 a |= b Roughly equivalent to a = a | b (2) 694 a ^= b Roughly equivalent to a = a ^ b (2) 695 a >>= b Roughly equivalent to a = a >> b (2) 696 a <<= b Roughly equivalent to a = a << b (2) 697 698 Notes : 699 (1) Can unpack tuples, lists, and strings. 700 first, second = a[0:2]; [f, s] = range(2); c1,c2,c3='abc' 701 Tip: x,y = y,x swaps x and y. 702 (2) Not exactly equivalent - a is evaluated only once. Also, where 703 possible, operation performed in-place - a is modified rather than 704 replaced. 705 706 Control Flow 707 708 if condition: suite 709 [elif condition: suite]* 710 [else: suite] -- usual if/else_if/else statement 711 while condition: suite 712 [else: suite] 713 -- usual while statement. "else" suite is executed 714 after loop exits, unless the loop is exited with 715 "break" 716 for element in sequence: suite 717 [else: suite] 718 -- iterates over sequence, assigning each element to element. 719 Use built-in range function to iterate a number of times. 720 "else" suite executed at end unless loop exited 721 with "break" 722 break -- immediately exits "for" or "while" loop 723 continue -- immediately does next iteration of "for" or "while" loop 724 return [result] -- Exits from function (or method) and returns result (use a tuple to 725 return more than one value). If no result given, then returns None. 726 yield result -- Freezes the execution frame of a generator and returns the result 727 to the iterator's .next() method. Upon the next call to next(), 728 resumes execution at the frozen point with all of the local variables 729 still intact. 730 731 Exception Statements 732 733 assert expr[, message] 734 -- expr is evaluated. if false, raises exception AssertionError 735 with message. Inhibited if __debug__ is 0. 736 try: suite1 737 [except [exception [, value]: suite2]+ 738 [else: suite3] 739 -- statements in suite1 are executed. If an exception occurs, look 740 in "except" clauses for matching <exception>. If matches or bare 741 "except" execute suite of that clause. If no exception happens 742 suite in "else" clause is executed after suite1. 743 If exception has a value, it is put in value. 744 exception can also be tuple of exceptions, e.g. 745 "except (KeyError, NameError), val: print val" 746 try: suite1 747 finally: suite2 748 -- statements in suite1 are executed. If no 749 exception, execute suite2 (even if suite1 is 750 exited with a "return", "break" or "continue" 751 statement). If exception did occur, executes 752 suite2 and then immediately reraises exception. 753 raise exception [,value [, traceback]] 754 -- raises exception with optional value 755 value. Arg traceback specifies a traceback object to 756 use when printing the exception's backtrace. 757 raise -- a raise statement without arguments re-raises 758 the last exception raised in the current function 759An exception is either a string (object) or a class instance. 760 Can create a new one simply by creating a new string: 761 762 my_exception = 'You did something wrong' 763 try: 764 if bad: 765 raise my_exception, bad 766 except my_exception, value: 767 print 'Oops', value 768 769Exception classes must be derived from the predefined class: Exception, e.g.: 770 class text_exception(Exception): pass 771 try: 772 if bad: 773 raise text_exception() 774 # This is a shorthand for the form 775 # "raise <class>, <instance>" 776 except Exception: 777 print 'Oops' 778 # This will be printed because 779 # text_exception is a subclass of Exception 780When an error message is printed for an unhandled exception which is a 781class, the class name is printed, then a colon and a space, and 782finally the instance converted to a string using the built-in function 783str(). 784All built-in exception classes derives from StandardError, itself 785derived from Exception. 786 787Name Space Statements 788 789[1.51: On Mac & Windows, the case of module file names must now match the case 790as used 791 in the import statement] 792Packages (>1.5): a package is a name space which maps to a directory including 793 module(s) and the special initialization module '__init__.py' 794 (possibly empty). Packages/dirs can be nested. You address a 795 module's symbol via '[package.[package...]module.symbol's. 796import module1 [as name1] [, module2]* 797 -- imports modules. Members of module must be 798 referred to by qualifying with [package.]module name: 799 "import sys; print sys.argv:" 800 "import package1.subpackage.module; package1.subpackage.module.foo()" 801 module1 renamed as name1, if supplied. 802from module import name1 [as othername1] [, name2]* 803 -- imports names from module module in current namespace. 804 "from sys import argv; print argv" 805 "from package1 import module; module.foo()" 806 "from package1.module import foo; foo()" 807 name1 renamed as othername1, if supplied. 808from module import * 809 -- imports all names in module, except those starting with "_"; 810 *to be used sparsely, beware of name clashes* : 811 "from sys import *; print argv" 812 "from package.module import *; print x' 813 NB: "from package import *" only imports the symbols defined 814 in the package's __init__.py file, not those in the 815 template modules! 816global name1 [, name2]* 817 -- names are from global scope (usually meaning from module) 818 rather than local (usually meaning only in function). 819 -- E.g. in fct without "global" statements, assuming 820 "a" is name that hasn't been used in fct or module 821 so far: 822 -Try to read from "a" -> NameError 823 -Try to write to "a" -> creates "a" local to fcn 824 -If "a" not defined in fct, but is in module, then 825 -Try to read from "a", gets value from module 826 -Try to write to "a", creates "a" local to fct 827 But note "a[0]=3" starts with search for "a", 828 will use to global "a" if no local "a". 829 830Function Definition 831 832def func_id ([param_list]): suite 833 -- Creates a function object & binds it to name func_id. 834 835 param_list ::= [id [, id]*] 836 id ::= value | id = value | *id | **id 837 [Args are passed by value.Thus only args representing a mutable object 838 can be modified (are inout parameters). Use a tuple to return more than 839 one value] 840 841Example: 842 def test (p1, p2 = 1+1, *rest, **keywords): 843 -- Parameters with "=" have default value (v is 844 evaluated when function defined). 845 If list has "*id" then id is assigned a tuple of 846 all remaining args passed to function (like C vararg) 847 If list has "**id" then id is assigned a dictionary of 848 all extra arguments passed as keywords. 849 850Class Definition 851 852class <class_id> [(<super_class1> [,<super_class2>]*)]: <suite> 853 -- Creates a class object and assigns it name <class_id> 854 <suite> may contain local "defs" of class methods and 855 assignments to class attributes. 856Example: 857 class my_class (class1, class_list[3]): ... 858 Creates a class object inheriting from both "class1" and whatever 859 class object "class_list[3]" evaluates to. Assigns new 860 class object to name "my_class". 861 - First arg to class methods is always instance object, called 'self' 862 by convention. 863 - Special method __init__() is called when instance is created. 864 - Special method __del__() called when no more reference to object. 865 - Create instance by "calling" class object, possibly with arg 866 (thus instance=apply(aClassObject, args...) creates an instance!) 867 - In current implementation, can't subclass off built-in 868 classes. But can "wrap" them, see UserDict & UserList modules, 869 and see __getattr__() below. 870Example: 871 class c (c_parent): 872 def __init__(self, name): self.name = name 873 def print_name(self): print "I'm", self.name 874 def call_parent(self): c_parent.print_name(self) 875 instance = c('tom') 876 print instance.name 877 'tom' 878 instance.print_name() 879 "I'm tom" 880 Call parent's super class by accessing parent's method 881 directly and passing "self" explicitly (see "call_parent" 882 in example above). 883 Many other special methods available for implementing 884 arithmetic operators, sequence, mapping indexing, etc. 885 886Documentation Strings 887 888Modules, classes and functions may be documented by placing a string literal by 889itself as the first statement in the suite. The documentation can be retrieved 890by getting the '__doc__' attribute from the module, class or function. 891Example: 892 class C: 893 "A description of C" 894 def __init__(self): 895 "A description of the constructor" 896 # etc. 897Then c.__doc__ == "A description of C". 898Then c.__init__.__doc__ == "A description of the constructor". 899 900Others 901 902lambda [param_list]: returnedExpr 903 -- Creates an anonymous function. returnedExpr must be 904 an expression, not a statement (e.g., not "if xx:...", 905 "print xxx", etc.) and thus can't contain newlines. 906 Used mostly for filter(), map(), reduce() functions, and GUI callbacks.. 907List comprehensions 908result = [expression for item1 in sequence1 [if condition1] 909 [for item2 in sequence2 ... for itemN in sequenceN] 910 ] 911is equivalent to: 912result = [] 913for item1 in sequence1: 914 for item2 in sequence2: 915 ... 916 for itemN in sequenceN: 917 if (condition1) and furthur conditions: 918 result.append(expression) 919 920 921 922Built-In Functions 923 924 Built-In Functions 925 Function Result 926__import__(name[, Imports module within the given context (see lib ref for 927globals[, locals[, more details) 928fromlist]]]) 929abs(x) Return the absolute value of number x. 930apply(f, args[, Calls func/method f with arguments args and optional 931keywords]) keywords. 932bool(x) Returns True when the argument x is true and False otherwise. 933buffer(obj) Creates a buffer reference to an object. 934callable(x) Returns True if x callable, else False. 935chr(i) Returns one-character string whose ASCII code isinteger i 936classmethod(f) Converts a function f, into a method with the class as the 937 first argument. Useful for creating alternative constructors. 938cmp(x,y) Returns negative, 0, positive if x <, ==, > to y 939coerce(x,y) Returns a tuple of the two numeric arguments converted to a 940 common type. 941 Compiles string into a code object.filename is used in 942 error message, can be any string. It isusually the file 943compile(string, from which the code was read, or eg. '<string>'if not read 944filename, kind) from file.kind can be 'eval' if string is a single stmt, or 945 'single' which prints the output of expression statements 946 thatevaluate to something else than None, or be 'exec'. 947complex(real[, Builds a complex object (can also be done using J or j 948image]) suffix,e.g. 1+3J) 949delattr(obj, name) deletes attribute named name of object obj <=> del obj.name 950 If no args, returns the list of names in current 951dict([items]) Create a new dictionary from the specified item list. 952dir([object]) localsymbol table. With a module, class or class 953 instanceobject as arg, returns list of names in its attr. 954 dict. 955divmod(a,b) Returns tuple of (a/b, a%b) 956enumerate(seq) Return a iterator giving: (0, seq[0]), (1, seq[1]), ... 957eval(s[, globals[, Eval string s in (optional) globals, locals contexts.s must 958locals]]) have no NUL's or newlines. s can also be acode object. 959 Example: x = 1; incr_x = eval('x + 1') 960execfile(file[, Executes a file without creating a new module, unlike 961globals[, locals]]) import. 962file() Synonym for open(). 963filter(function, Constructs a list from those elements of sequence for which 964sequence) function returns true. function takes one parameter. 965float(x) Converts a number or a string to floating point. 966getattr(object, [<default> arg added in 1.5.2]Gets attribute called name 967name[, default])) from object,e.g. getattr(x, 'f') <=> x.f). If not found, 968 raisesAttributeError or returns default if specified. 969globals() Returns a dictionary containing current global variables. 970hasattr(object, Returns true if object has attr called name. 971name) 972hash(object) Returns the hash value of the object (if it has one) 973help(f) Display documentation on object f. 974hex(x) Converts a number x to a hexadecimal string. 975id(object) Returns a unique 'identity' integer for an object. 976input([prompt]) Prints prompt if given. Reads input and evaluates it. 977 Converts a number or a string to a plain integer. Optional 978int(x[, base]) base paramenter specifies base from which to convert string 979 values. 980intern(aString) Enters aString in the table of "interned strings" 981 andreturns the string. Interned strings are 'immortals'. 982isinstance(obj, returns true if obj is an instance of class. Ifissubclass 983class) (A,B) then isinstance(x,A) => isinstance(x,B) 984issubclass(class1, returns true if class1 is derived from class2 985class2) 986 Returns the length (the number of items) of an object 987iter(collection) Returns an iterator over the collection. 988len(obj) (sequence, dictionary, or instance of class implementing 989 __len__). 990list(sequence) Converts sequence into a list. If already a list,returns a 991 copy of it. 992locals() Returns a dictionary containing current local variables. 993 Converts a number or a string to a long integer. Optional 994long(x[, base]) base paramenter specifies base from which to convert string 995 values. 996 Applies function to every item of list and returns a listof 997map(function, list, the results. If additional arguments are passed,function 998...) must take that many arguments and it is givento function on 999 each call. 1000max(seq) Returns the largest item of the non-empty sequence seq. 1001min(seq) Returns the smallest item of a non-empty sequence seq. 1002oct(x) Converts a number to an octal string. 1003open(filename [, Returns a new file object. First two args are same asthose 1004mode='r', [bufsize= for C's "stdio open" function. bufsize is 0for unbuffered, 1005implementation 1 for line-buffered, negative forsys-default, all else, of 1006dependent]]) (about) given size. 1007ord(c) Returns integer ASCII value of c (a string of len 1). Works 1008 with Unicode char. 1009object() Create a base type. Used as a superclass for new-style objects. 1010open(name Open a file. 1011 [, mode 1012 [, buffering]]) 1013pow(x, y [, z]) Returns x to power y [modulo z]. See also ** operator. 1014property() Created a property with access controlled by functions. 1015range(start [,end Returns list of ints from >= start and < end.With 1 arg, 1016[, step]]) list from 0..arg-1With 2 args, list from start..end-1With 3 1017 args, list from start up to end by step 1018raw_input([prompt]) Prints prompt if given, then reads string from stdinput (no 1019 trailing \n). See also input(). 1020reduce(f, list [, Applies the binary function f to the items oflist so as to 1021init]) reduce the list to a single value.If init given, it is 1022 "prepended" to list. 1023 Re-parses and re-initializes an already imported module. 1024 Useful in interactive mode, if you want to reload amodule 1025reload(module) after fixing it. If module was syntacticallycorrect but had 1026 an error in initialization, mustimport it one more time 1027 before calling reload(). 1028 Returns a string containing a printable and if possible 1029repr(object) evaluable representation of an object. <=> `object` 1030 (usingbackquotes). Class redefinissable (__repr__). See 1031 also str() 1032round(x, n=0) Returns the floating point value x rounded to n digitsafter 1033 the decimal point. 1034setattr(object, This is the counterpart of getattr().setattr(o, 'foobar', 1035name, value) 3) <=> o.foobar = 3Creates attribute if it doesn't exist! 1036slice([start,] stop Returns a slice object representing a range, with R/ 1037[, step]) Oattributes: start, stop, step. 1038 Returns a string containing a nicely 1039staticmethod() Convert a function to method with no self or class 1040 argument. Useful for methods associated with a class that 1041 do not need access to an object's internal state. 1042str(object) printablerepresentation of an object. Class overridable 1043 (__str__).See also repr(). 1044super(type) Create an unbound super object. Used to call cooperative 1045 superclass methods. 1046sum(sequence, Add the values in the sequence and return the sum. 1047 [start]) 1048tuple(sequence) Creates a tuple with same elements as sequence. If already 1049 a tuple, return itself (not a copy). 1050 Returns a type object [see module types] representing 1051 thetype of obj. Example: import typesif type(x) == 1052type(obj) types.StringType: print 'It is a string'NB: it is 1053 recommanded to use the following form:if isinstance(x, 1054 types.StringType): etc... 1055unichr(code) code. 1056unicode(string[, Creates a Unicode string from a 8-bit string, using 1057encoding[, error thegiven encoding …
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