Python Pocket Reference 4th Edition Book
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Python in Your Pocketÿm
Python! Pocket Reference
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O’REILLY'
Mark Lutz
Programming Languages
O’REILLY Python Pocket Reference This handy book is an easy-to-use reference to the core language, with descriptions of commonly used modules and toolkits, and a guide to recent changes, new features, and upgraded built-ins all updated to cover Python 3.X as well as version 2.6.
—
— —
widely recognized as the world's leading Python trainer Python Pocket Reference, Fourth Edition, is the perfect companion to his classic Python tutorials, Learning Python and Programming Python (both O’Reilly).
Written by Mark Lutz
This edition covers: Built-in object types, including numbers, lists, dictionaries, and more Statements and syntax for creating and processing objects Functions and modules for structuring and reusing code
Python's object-oriented programming tools The exception-handling model Built-in functions, exceptions, and attributes
Special operator overloading methods Widely used standard library modules and extensions Command-line options and development tools
Python idioms and hints Mark Lutz, a pioneering figure in the Python community since 1992, has written some of the earliest and bestselling texts on Python.
oreilly.com US $14.99
CAN $18.99
ISBN: 978-0-596-15808-8
5 14 9 9 9
7805961 58088
Safari Books Online
Free online edition for 45 days with purchase of this book. Details on last page.
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FOURTH EDITION
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O REILLY Beijing • Cambridge • Farnham • Köln • Sebastopol • Taipei • Tokyo
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Contents
Python Pocket Reference Introduction Conventions Command-Line Options Python Options Program Specification Environment Variables Operational Variables Command-Line Option Variables Built-in Types and Operators Operators and Precedence Operator Usage Notes Operations by Category Sequence Operation Notes Specific Built-in Types Numbers Strings Unicode Strings Lists Dictionaries Tuples Files
1 1 2 4 4 6 7 7 8 8 8 10 11 15 16 16 19 33 36 41 44 45 v
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Sets Other Common Types Type Conversions Statements and Syntax Syntax Rules Name Rules Specific Statements The Assignment Statement The Expression Statement The print Statement The if Statement The while Statement The for Statement The pass Statement The break Statement The continue Statement The del Statement The def Statement The return Statement The yield Statement The global Statement The nonlocal Statement The import Statement The from Statement The class Statement The try Statement The raise Statement The assert Statement The with Statement Python 2.X Statements Namespace and Scope Rules Qualified Names: Object Namespaces vi | Table of Contents
49 51 52 53 53 54 56 57 59 60 62 62 63 63 63 64 64 64 68 68 70 70 71 72 73 75 78 80 80 82 82 83
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Unqualified Names: Lexical Scopes Statically Nested Scopes Object-Oriented Programming Classes and Instances Pseudoprivate Attributes New Style Classes Operator Overloading Methods For All Types For Collections (Sequences, Mappings) For Numbers (Binary Operators) For Numbers (Other Operations) For Descriptors For Context Managers Python 2.X Operator Overloading Methods Built-in Functions Python 2.X Built-in Functions Built-in Exceptions Superclasses (Categories) Specific Exceptions Raised Warning Category Exceptions Warnings Framework Python 2.X Built-in Exceptions Built-in Attributes Standard Library Modules The sys Module The string Module Module Functions and Classes Constants The os System Module Administrative Tools Portability Constants Shell Commands
83 84 85 85 86 87 88 88 93 94 97 98 99 99 102 119 124 124 125 129 130 131 131 132 133 139 139 140 141 141 142 143
Table of Contents | vii
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Environment Tools File Descriptor Tools File Pathname Tools Process Control The os.path Module The re Pattern-Matching Module Module Functions Regular Expression Objects Match Objects Pattern Syntax Object Persistence Modules dbm and shelve Modules pickle Module The tkinter GUI Module and Tools tkinter Example tkinter Core Widgets Common Dialog Calls Additional tkinter Classes and Tools Tcl/Tk-to-Python/tkinter Mappings Internet Modules and Tools Commonly Used Library Modules Other Standard Library Modules The math Module The time Module The datetime Module Threading Modules Binary Data Parsing Python Portable SQL Database API API Usage Example Module Interface Connection Objects Cursor Objects viii | Table of Contents
144 145 147 150 153 155 155 157 158 159 163 164 166 168 168 169 170 171 171 173 173 175 176 176 177 177 178 179 179 180 181 181
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Type Objects and Constructors Python Idioms and Hints Core Language Hints Environment Hints Usage Hints Assorted Hints Index
182 183 183 184 185 187 189
Table of Contents | ix
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Python Pocket Reference
Introduction 3\WKRQLVDJHQHUDOSXUSRVHREMHFWRULHQWHGDQGRSHQVRXUFH FRPSXWHU SURJUDPPLQJ ODQJXDJH ,W LV FRPPRQO\ XVHG IRU ERWKVWDQGDORQHSURJUDPVDQGVFULSWLQJDSSOLFDWLRQVLQDZLGH YDULHW\RIGRPDLQVE\KXQGUHGVRIWKRXVDQGVRIGHYHORSHUV 3\WKRQ LV GHVLJQHG WR RSWLPL]H GHYHORSHU SURGXFWLYLW\ VRIW ZDUHTXDOLW\SURJUDPSRUWDELOLW\DQGFRPSRQHQWLQWHJUDWLRQ 3\WKRQSURJUDPVUXQRQPRVWSODWIRUPVLQFRPPRQXVHLQ FOXGLQJ PDLQIUDPHV DQG VXSHUFRPSXWHUV 8QL[ DQG /LQX[ :LQGRZVDQG0DFLQWRVK-DYDDQG1(7DQGPRUH 7KLV SRFNHW UHIHUHQFH VXPPDUL]HV 3\WKRQ W\SHV DQG VWDWH PHQWV VSHFLDO PHWKRG QDPHV EXLOWLQ IXQFWLRQV DQG H[FHS WLRQV FRPPRQO\ XVHG VWDQGDUG OLEUDU\ PRGXOHV DQG RWKHU SURPLQHQW 3\WKRQ WRROV ,W LV LQWHQGHG WR VHUYH DV D FRQFLVH UHIHUHQFHWRROIRUGHYHORSHUVDQGLVGHVLJQHGWREHDFRPSDQLRQ WRRWKHUERRNVWKDWSURYLGHWXWRULDOVFRGHH[DPSOHVDQGRWKHU OHDUQLQJPDWHULDOV
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2 | Python Pocket Reference
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22 | Python Pocket Reference
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>>> '{0}, {food}'.format(42, food='spam') '42, spam' >>> import sys >>> fmt = '{0.platform} {1[x]} {2[0]}' # attr,key,index >>> fmt.format(sys, {'x': 'ham', 'y': 'eggs'}, 'AB') 'win32 ham A' >>> '{0} {1:+.2f}'.format(1 / 3.0, 1 / 3.0) '0.333333333333 +0.33' >>> '{0:.{1}f}'.format(1 / 3.0, 4) '0.3333'
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24 | Python Pocket Reference
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Specific Built-in Types | 25
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Template string substitution ,Q3\WKRQDQGODWHUDQRWKHUIRUPRIVLPSOHVWULQJVXEVWL WXWLRQLVSURYLGHGDVDQDOWHUQDWLYHWRWKHVWULQJIRUPDWWLQJH[ SUHVVLRQDQGPHWKRGGHVFULEHGLQWKHSULRUVHFWLRQV7KHXVXDO ZD\RIVXEVWLWXWLQJYDULDEOHVLVZLWKWKH%RSHUDWRU >>> '%(page)i: %(title)s' % {'page':2, 'title': 'PyRef4E'} '2: PyRef4E'
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26 | Python Pocket Reference
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7DEOH 3\WKRQVWULQJPHWKRGFDOOV S.capitalize() S.center(width, [, fill]) S.count(sub [, start [, end]]) S.encode([encoding [,errors]]) S.endswith(suffix [, start [, end]]) S.expandtabs([tabsize]) S.find(sub [, start [, end]]) S.format(fmtstr, *args, **kwargs) S.index(sub [, start [, end]]) S.isalnum() S.isalpha() S.isdecimal() S.isdigit() S.isidentifier() S.islower() S.isnumeric() S.isprintable() S.isspace() S.istitle( S.isupper() S.join(iterable) S.ljust(width [, fill]) S.lower() S.lstrip([chars]) S.maketrans(x[, y[, z]]) S.partition(sep) S.replace(old, new [, count]) S.rfind(sub [,start [,end]]) S.rindex(sub [, start [, end]])
Specific Built-in Types | 27
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S.rjust(width [, fill]) S.rpartition(sep) S.rsplit([sep[, maxsplit]]) S.rstrip([chars]) S.split([sep [,maxsplit]]) S.splitlines([keepends]) S.startswith(prefix [, start [, end]]) S.strip([chars]) S.swapcase() S.title() S.translate(map) S.upper() S.zfill(width)
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28 | Python Pocket Reference
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>>> set(dir(bytes)) - set(dir(str)) {'decode', 'fromhex'} >>> set(dir(bytearray)) - set(dir(bytes)) {'insert', '__alloc__', 'reverse', 'extend', '__delitem__', 'pop', '__setitem__', '__iadd__', 'remove', 'append', '__imul__'}
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38 | Python Pocket Reference
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40 | Python Pocket Reference
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adict.clear()
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The Assignment Statement target = expression target1 = target2 = expression target1, target2 = expression1, expression2 target1 += expression target1, target2, ... = same-length-iterable (target1, target2, ...) = same-length-iterable [target1, target2, ...] = same-length-iterable target1, *target2, ... = matching–length-iterable
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The Expression Statement expression function([value, name=value, *name, **name...]) object.method([value, name=value, *name, **name...])
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(DFKvalueGHQRWHVDQREMHFWWREHSULQWHG7KLVFDOOLVFRQILJ XUHGE\LWVWKUHHNH\ZRUGRQO\DUJXPHQWV sepLVDVWULQJWRSODFHEHWZHHQYDOXHV GHIDXOWVWRDVSDFH ' ' endLVDVWULQJWRSODFHDWWKHHQGRIWKHWH[WSULQWHG GH IDXOWVWRDQHZOLQH '\n' fileLVWKHILOHOLNHREMHFWWRZKLFKWH[WLVZULWWHQ GHIDXOWV WRVWDQGDUGRXWSXW sys.stdout 3DVVHPSW\RUFXVWRPVWULQJVWRVXSSUHVVVSDFHVHSDUDWRUVDQG OLQHIHHGVDQGSDVVDILOHRUILOHOLNHREMHFWWRUHGLUHFWRXWSXW LQ\RXUVFULSW >>> print(2 ** 32, 'spam') 4294967296 spam >>> print(2 ** 32, 'spam', sep='') 4294967296spam >>> print(2 ** 32, 'spam', end=' '); print(1, 2, 3) 4294967296 spam 1 2 3 >>> print(2 ** 32, 'spam', sep='', file=open('out', 'w'))
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>>> open('out').read() '4294967296spam\n'
%HFDXVHE\GHIDXOWprintVLPSO\FDOOVWKHwritePHWKRGRIWKH REMHFW FXUUHQWO\ UHIHUHQFHG E\ sys.stdout WKH IROORZLQJ LV HTXLYDOHQWWRprint(X) import sys sys.stdout.write(str(X) + '\n')
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# any object with a write() # goes to object's write()
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Python 2.X print statements ,Q3\WKRQ;SULQWLQJLVDVSHFLILFVWDWHPHQWLQVWHDGRIDEXLOW LQIXQFWLRQRIWKHIROORZLQJIRUP print [value [, value]* [,]] print >> file [, value [, value]* [,]]
7KH3\WKRQ; printVWDWHPHQWGLVSOD\VWKHSULQWDEOHUHSUH VHQWDWLRQRIYDOXHVRQWKHstdoutVWUHDP WKHFXUUHQWVHWWLQJRI sys.stdout DQG DGGV VSDFHV EHWZHHQ YDOXHV 7KH WUDLOLQJ FRPPDVXSSUHVVHVWKHOLQHIHHGWKDWLVQRUPDOO\DGGHGDWWKH HQGRIDOLVWDQGLVHTXLYDOHQWWRXVLQJend=' 'LQ3\WKRQ >>> print 2 ** 32, 'spam' 4294967296 spam >>> print 2 ** 32, 'spam',; print 1, 2, 3 4294967296 spam 1 2 3
Specific Statements | 61
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7KH3\WKRQ;printVWDWHPHQWFDQDOVRQDPHDQRSHQRXWSXW ILOHOLNHREMHFWWREHWKHWDUJHWRIWKHSULQWHGWH[WLQVWHDGRI sys.stdout fileobj = open('log', 'a') print >> fileobj, "Warning-bad spam!"
,IWKHILOHREMHFWLV None sys.stdoutLVXVHG7KLV3\WKRQ; >>V\QWD[LVHTXLYDOHQWWRWKHfile=FNH\ZRUGDUJXPHQWLQ3\ WKRQ 7KHUH LV QR HTXLYDOHQW WR sep=S LQ 3\WKRQ ¦V VWDWHPHQW 7RXVHWKH3\WKRQSULQWLQJIXQFWLRQLQ3\WKRQ;UXQWKH IROORZLQJ from __future__ import print_function
The if Statement if test: suite [elif test: suite]* [else: suite]
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The while Statement while test: suite [else: suite]
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62 | Python Pocket Reference
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The for Statement for target in iterable: suite [else: suite]
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The pass Statement pass
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Specific Statements | 63
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The continue Statement continue
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The del Statement del del del del
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64 | Python Pocket Reference
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7DEOH$UJXPHQWIRUPDWVLQGHILQLWLRQV Argument format
Interpretation
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Matched by name or position
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Python 3.0 keyword-only arguments after *
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Same as prior line
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Interpretation
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Python 3.0 keyword-only arguments 3\WKRQJHQHUDOL]HVIXQFWLRQGHILQLWLRQWRDOORZNH\ZRUG RQO\DUJXPHQWVZKLFKPXVWEHSDVVHGE\NH\ZRUGDQGDUH UHTXLUHGLIQRWFRGHGZLWKGHIDXOWV.H\ZRUGRQO\DUJXPHQWV DUHFRGHGDIWHUWKH*ZKLFKPD\DSSHDUZLWKRXWDQDPHLIWKHUH DUHNH\ZRUGRQO\DUJXPHQWVEXWQRWDUELWUDU\SRVLWLRQDOV >>> def f(a, *b, c): print(a, b, c) ... >>> f(1, 2, c=3) 1 (2,) 3
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Specific Statements | 65
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Python 3.0 function annotations 3\WKRQDOVRJHQHUDOL]HVIXQFWLRQGHILQLWLRQWRDOORZDUJX PHQWVDQGUHWXUQYDOXHVWREHDQQRWDWHGZLWKREMHFWYDOXHVIRU XVHLQH[WHQVLRQV$QQRWDWLRQVDUHFRGHGDV :valueDIWHUWKH DUJXPHQWQDPHDQGEHIRUHDGHIDXOWDQG->valueDIWHUWKHDU JXPHQWOLVW7KH\DUHFROOHFWHGLQWRDQ__annotations__DWWULE XWHEXWDUHQRWRWKHUZLVHWUHDWHGDVVSHFLDOE\3\WKRQLWVHOI >>> def f(a:99, b:'spam'=None) -> float: ... print(a, b) ... >>> f(88) 88 None >>> f.__annotations__ {'a': 99, 'b': 'spam', 'return': }
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Defaults and attributes 0XWDEOH GHIDXOW DUJXPHQW YDOXHV DUH HYDOXDWHG RQFH DW def VWDWHPHQWWLPHQRWRQHDFKFDOODQGVRFDQUHWDLQVWDWHEH WZHHQFDOOV+RZHYHUVRPHFRQVLGHUWKLVEHKDYLRUWREHDFDY HDWDQGFODVVHVDQGHQFORVLQJVFRSHUHIHUHQFHVDUHRIWHQEHWWHU VWDWHUHWHQWLRQWRROV XVHNoneGHIDXOWVIRUPXWDEOHDQGH[SOLFLW WHVWVWRDYRLGFKDQJHVDVVKRZQLQWKHIROORZLQJ¦VFRPPHQWV >>> def grow(a, b=[]): ... b.append(a) ... print(b)
66 | Python Pocket Reference
# ..., b=None) # if b == None: b = []
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... >>> grow(1); grow(2) [1] [1, 2]
%RWK3\WKRQ;DQGDOVRVXSSRUWDWWDFKPHQWRIDUELWUDU\ DWWULEXWHV WR IXQFWLRQV DV DQRWKHU IRUP RI VWDWH UHWHQWLRQ WKRXJK DWWULEXWHV VXSSRUW RQO\ SHUIXQFWLRQREMHFW VWDWH ZKLFKLVRQO\SHUFDOOLIHDFKFDOOJHQHUDWHVDQHZIXQFWLRQ >>> grow.food = 'spam' >>> grow.food 'spam'
Function and method decorators $VRI3\WKRQIXQFWLRQGHILQLWLRQVFDQEHSUHFHGHGE\D GHFODUDWLRQ V\QWD[ WKDW GHVFULEHV WKH IXQFWLRQ WKDW IROORZV .QRZQDVGHFRUDWRUVDQGFRGHGZLWKDQ@FKDUDFWHUWKHVHGHF ODUDWLRQVSURYLGHH[SOLFLWV\QWD[IRUIXQFWLRQDOWHFKQLTXHV7KH IXQFWLRQGHFRUDWRUV\QWD[ @decorator def F(): ...
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@C def f(): ...
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VWDWHPHQW 8VH D return VWDWHPHQW ZLWK QR YDOXH WR HQG WKH LWHUDWLRQRUVLPSO\IDOORIIWKHHQGRIWKHIXQFWLRQ def generateSquares(N): for i in range(N): yield i ** 2 >>> G = generateSquares(5) >>> list(G) [0, 1, 4, 9, 16]
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Package imports ,I XVHG WKH package SUHIL[ QDPHV JLYH HQFORVLQJ GLUHFWRU\ QDPHVDQGPRGXOHGRWWHGSDWKVUHIOHFWGLUHFWRU\KLHUDUFKLHV $QLPSRUWRIWKHIRUP import dir1.dir2.modJHQHUDOO\ORDGV WKHPRGXOHILOHDWGLUHFWRU\SDWKGLUGLUPRGS\ZKHUHGLU PXVWEHFRQWDLQHGE\DGLUHFWRU\OLVWHGRQWKHPRGXOHVHDUFK SDWKsys.path (DFKGLUHFWRU\OLVWHGLQDQLPSRUWVWDWHPHQWPXVWKDYHD SRV VLEO\HPSW\ __init__.pyILOHWKDWVHUYHVDVWKHGLUHFWRU\OHYHO¦V PRGXOHQDPHVSDFH7KLVILOHLVUXQRQWKHILUVWLPSRUWWKURXJK WKHGLUHFWRU\DQGDOOQDPHVDVVLJQHGLQ __init__.pyILOHVEH FRPH DWWULEXWHV RI WKH GLUHFWRU\¦V PRGXOH REMHFW 'LUHFWRU\ SDFNDJHVFDQUHVROYHFRQIOLFWVFDXVHGE\WKHOLQHDUQDWXUHRI PYTHONPATH 6HHDOVR£3DFNDJHUHODWLYHLPSRUWV\QWD[¤RQSDJH
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SystemExit
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128 | Python Pocket Reference
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ValueError
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:DUQLQJV DERXW IHDWXUHV WKDW ZLOO EH GHSUHFDWHG LQ WKH IXWXUH SyntaxWarning
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,QDGGLWLRQ\RXFDQDGGILOWHUVWRGLVDEOHFHUWDLQZDUQLQJV>> import re >>> patt = re.compile('hello[ \t]*(.*)') >>> mobj = patt.match('hello world!') >>> mobj.group(1) 'world!'
The re Pattern-Matching Module | 159
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$
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C
Any nonspecial character matches itself.
R*
Zero or more occurrences of preceding regular expression R (as many as possible).
R+
One or more occurrences of preceding regular expression R (as many as possible).
R?
Zero or one occurrence of preceding regular expression R.
R{m}
Matches exactly m repetitions of preceding regular expression R.
R{m,n}
Matches from m to n repetitions of preceding regular expression R.
R*?, R+?, R??, R{m,n}?
Same as *, +, and ?, but matches as few characters/times as possible; nongreedy.
[...]
Defines character set; e.g., [a-zA-Z] matches all letters (also see Table 20).
160 | Python Pocket Reference
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Form
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Escapes special characters (e.g., *?+|()) and introduces special sequences (see Table 20). Due to Python rules, write as \\ or r'\\'.
\\
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RR
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Matches any RE inside (), and delimits a group (retains matched substring).
(?: R)
Same as (R) but doesn’t delimit a group.
(?= R)
Look-ahead assertion: matches if R matches next, but doesn’t consume any of the string (e.g., X (?=Y) matches X if followed by Y).
(?! R)
Negative look-ahead assertion: matches if R doesn’t match next. Negative of (?=R).
(?P R)
Matches any RE inside () and delimits a named group (e.g., r'(?P[a-zA-Z_]\ w*)' defines a group named id).
The re Pattern-Matching Module | 161
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Form
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(?P=name)
Matches whatever text was matched by the earlier group named name.
(?#...)
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(?letter)
letter is one of a, i, L, m, s, x, or u. Set flag (re.A, re.I, re.L, etc.) for entire RE.
(?if', 1, 2.0)) 8 >>> open('data', 'rb').read() b'\x00\x00\x00\x01@\x00\x00\x00' >>> struct.unpack('>if', open('data', 'rb').read()) (1, 2.0)
Python Portable SQL Database API 3\WKRQ¦VSRUWDEOH64/GDWDEDVH$3,SURYLGHVVFULSWSRUWDELOLW\ EHWZHHQGLIIHUHQWYHQGRUVSHFLILF64/GDWDEDVHSDFNDJHV)RU HDFKYHQGRULQVWDOOWKHYHQGRUVSHFLILFH[WHQVLRQPRGXOHEXW ZULWH\RXUVFULSWVDFFRUGLQJWRWKHSRUWDEOHGDWDEDVH$3,>> from sqlite3 import connect >>> conn = connect(r'C:\users\mark\misc\temp.db') >>> curs = conn.cursor() >>> >>> >>> >>>
curs.execute('create table jobs (name, title, pay)') prefix = 'insert into jobs values ' curs.execute(prefix + "('Bob', 'dev', 100)") curs.execute(prefix + "('Sue', 'dev', 120)")
>>> curs.execute("select * from jobs where pay > 100") >>> for (name, title, pay) in curs.fetchall(): ... print(name, title, pay) ... Sue dev 120 >>> curs.execute("select name, pay from jobs").fetchall() [('Bob', 100), ('Sue', 120)] >>> query = "select * from jobs where title = ?" >>> curs.execute(query, ('dev',)).fetchall() [('Bob', 'dev', 100), ('Sue', 'dev', 120)]
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Python! Pocket Reference
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O’REILLY'
Mark Lutz
Programming Languages
O’REILLY Python Pocket Reference This handy book is an easy-to-use reference to the core language, with descriptions of commonly used modules and toolkits, and a guide to recent changes, new features, and upgraded built-ins all updated to cover Python 3.X as well as version 2.6.
—
— —
widely recognized as the world's leading Python trainer Python Pocket Reference, Fourth Edition, is the perfect companion to his classic Python tutorials, Learning Python and Programming Python (both O’Reilly).
Written by Mark Lutz
This edition covers: Built-in object types, including numbers, lists, dictionaries, and more Statements and syntax for creating and processing objects Functions and modules for structuring and reusing code
Python's object-oriented programming tools The exception-handling model Built-in functions, exceptions, and attributes
Special operator overloading methods Widely used standard library modules and extensions Command-line options and development tools
Python idioms and hints Mark Lutz, a pioneering figure in the Python community since 1992, has written some of the earliest and bestselling texts on Python.
oreilly.com US $14.99
CAN $18.99
ISBN: 978-0-596-15808-8
5 14 9 9 9
7805961 58088
Safari Books Online
Free online edition for 45 days with purchase of this book. Details on last page.
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Python 3RFNHW5HIHUHQFH
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FOURTH EDITION
Python 3RFNHW5HIHUHQFH
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O REILLY Beijing • Cambridge • Farnham • Köln • Sebastopol • Taipei • Tokyo
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Python Pocket Reference, Fourth Edition E\0DUN/XW] &RS\ULJKW0DUN/XW]$OOULJKWVUHVHUYHG 3ULQWHGLQ&DQDGD 3XEOLVKHGE\2¦5HLOO\0HGLD,QF*UDYHQVWHLQ+LJKZD\1RUWK6H EDVWRSRO&$ 2¦5HLOO\ERRNVPD\EHSXUFKDVHGIRUHGXFDWLRQDOEXVLQHVVRUVDOHVSURPR WLRQDOXVH2QOLQHHGLWLRQVDUHDOVRDYDLODEOHIRUPRVWWLWOHV KWWS P\VDIDUL ERRNVRQOLQHFRP )RUPRUHLQIRUPDWLRQFRQWDFWRXUFRUSRUDWHLQVWLWXWLRQDO VDOHVGHSDUWPHQW RUFRUSRUDWH#RUHLOO\FRP
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Contents
Python Pocket Reference Introduction Conventions Command-Line Options Python Options Program Specification Environment Variables Operational Variables Command-Line Option Variables Built-in Types and Operators Operators and Precedence Operator Usage Notes Operations by Category Sequence Operation Notes Specific Built-in Types Numbers Strings Unicode Strings Lists Dictionaries Tuples Files
1 1 2 4 4 6 7 7 8 8 8 10 11 15 16 16 19 33 36 41 44 45 v
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Sets Other Common Types Type Conversions Statements and Syntax Syntax Rules Name Rules Specific Statements The Assignment Statement The Expression Statement The print Statement The if Statement The while Statement The for Statement The pass Statement The break Statement The continue Statement The del Statement The def Statement The return Statement The yield Statement The global Statement The nonlocal Statement The import Statement The from Statement The class Statement The try Statement The raise Statement The assert Statement The with Statement Python 2.X Statements Namespace and Scope Rules Qualified Names: Object Namespaces vi | Table of Contents
49 51 52 53 53 54 56 57 59 60 62 62 63 63 63 64 64 64 68 68 70 70 71 72 73 75 78 80 80 82 82 83
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Unqualified Names: Lexical Scopes Statically Nested Scopes Object-Oriented Programming Classes and Instances Pseudoprivate Attributes New Style Classes Operator Overloading Methods For All Types For Collections (Sequences, Mappings) For Numbers (Binary Operators) For Numbers (Other Operations) For Descriptors For Context Managers Python 2.X Operator Overloading Methods Built-in Functions Python 2.X Built-in Functions Built-in Exceptions Superclasses (Categories) Specific Exceptions Raised Warning Category Exceptions Warnings Framework Python 2.X Built-in Exceptions Built-in Attributes Standard Library Modules The sys Module The string Module Module Functions and Classes Constants The os System Module Administrative Tools Portability Constants Shell Commands
83 84 85 85 86 87 88 88 93 94 97 98 99 99 102 119 124 124 125 129 130 131 131 132 133 139 139 140 141 141 142 143
Table of Contents | vii
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Environment Tools File Descriptor Tools File Pathname Tools Process Control The os.path Module The re Pattern-Matching Module Module Functions Regular Expression Objects Match Objects Pattern Syntax Object Persistence Modules dbm and shelve Modules pickle Module The tkinter GUI Module and Tools tkinter Example tkinter Core Widgets Common Dialog Calls Additional tkinter Classes and Tools Tcl/Tk-to-Python/tkinter Mappings Internet Modules and Tools Commonly Used Library Modules Other Standard Library Modules The math Module The time Module The datetime Module Threading Modules Binary Data Parsing Python Portable SQL Database API API Usage Example Module Interface Connection Objects Cursor Objects viii | Table of Contents
144 145 147 150 153 155 155 157 158 159 163 164 166 168 168 169 170 171 171 173 173 175 176 176 177 177 178 179 179 180 181 181
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Type Objects and Constructors Python Idioms and Hints Core Language Hints Environment Hints Usage Hints Assorted Hints Index
182 183 183 184 185 187 189
Table of Contents | ix
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Python Pocket Reference
Introduction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2 | Python Pocket Reference
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Using Code Examples 7KLVERRNLVKHUHWRKHOS\RXJHW\RXUMREGRQH,QJHQHUDO\RX PD\ XVH WKH FRGH LQ WKLV ERRN LQ \RXU SURJUDPV DQG GRFX PHQWDWLRQ>> '%s, %s, %.2f' % (42, 'spam', 1 / 3.0) '42, spam, 0.33' >>> '{0}, {1}, {2:.2f}'.format(42, 'spam', 1 / 3.0) '42, spam, 0.33'
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22 | Python Pocket Reference
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,QWKHIRUPDWVWULQJRQWKHOHIWRIWKH %RSHUDWRUVXEVWLWXWLRQ WDUJHWVKDYHWKHIROORZLQJJHQHUDOIRUPDW %[(keyname)][flags][width][.precision]typecode
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>>> '{0}, {food}'.format(42, food='spam') '42, spam' >>> import sys >>> fmt = '{0.platform} {1[x]} {2[0]}' # attr,key,index >>> fmt.format(sys, {'x': 'ham', 'y': 'eggs'}, 'AB') 'win32 ham A' >>> '{0} {1:+.2f}'.format(1 / 3.0, 1 / 3.0) '0.333333333333 +0.33' >>> '{0:.{1}f}'.format(1 / 3.0, 4) '0.3333'
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24 | Python Pocket Reference
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Specific Built-in Types | 25
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Template string substitution ,Q3\WKRQDQGODWHUDQRWKHUIRUPRIVLPSOHVWULQJVXEVWL WXWLRQLVSURYLGHGDVDQDOWHUQDWLYHWRWKHVWULQJIRUPDWWLQJH[ SUHVVLRQDQGPHWKRGGHVFULEHGLQWKHSULRUVHFWLRQV7KHXVXDO ZD\RIVXEVWLWXWLQJYDULDEOHVLVZLWKWKH%RSHUDWRU >>> '%(page)i: %(title)s' % {'page':2, 'title': 'PyRef4E'} '2: PyRef4E'
)RUVLPSOHUIRUPDWWLQJWDVNVDTemplateFODVVKDVEHHQDGGHG WRWKHstringPRGXOHWKDWXVHV$WRLQGLFDWHDVXEVWLWXWLRQ >>> >>> >>> '2:
import string t = string.Template('$page: $title') t.substitute({'page':2, 'title': 'PyRef4E'}) PyRef4E'
6XEVWLWXWLRQYDOXHVFDQEHSURYLGHGDVNH\ZRUGDUJXPHQWVRU GLFWLRQDU\NH\V >>> s = string.Template('$who likes $what') >>> s.substitute(who='bob', what=3.14) 'bob likes 3.14' >>> s.substitute(dict(who='bob', what='pie')) 'bob likes pie'
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26 | Python Pocket Reference
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7DEOH 3\WKRQVWULQJPHWKRGFDOOV S.capitalize() S.center(width, [, fill]) S.count(sub [, start [, end]]) S.encode([encoding [,errors]]) S.endswith(suffix [, start [, end]]) S.expandtabs([tabsize]) S.find(sub [, start [, end]]) S.format(fmtstr, *args, **kwargs) S.index(sub [, start [, end]]) S.isalnum() S.isalpha() S.isdecimal() S.isdigit() S.isidentifier() S.islower() S.isnumeric() S.isprintable() S.isspace() S.istitle( S.isupper() S.join(iterable) S.ljust(width [, fill]) S.lower() S.lstrip([chars]) S.maketrans(x[, y[, z]]) S.partition(sep) S.replace(old, new [, count]) S.rfind(sub [,start [,end]]) S.rindex(sub [, start [, end]])
Specific Built-in Types | 27
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S.rjust(width [, fill]) S.rpartition(sep) S.rsplit([sep[, maxsplit]]) S.rstrip([chars]) S.split([sep [,maxsplit]]) S.splitlines([keepends]) S.startswith(prefix [, start [, end]]) S.strip([chars]) S.swapcase() S.title() S.translate(map) S.upper() S.zfill(width)
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28 | Python Pocket Reference
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>>> set(dir(bytes)) - set(dir(str)) {'decode', 'fromhex'} >>> set(dir(bytearray)) - set(dir(bytes)) {'insert', '__alloc__', 'reverse', 'extend', '__delitem__', 'pop', '__setitem__', '__iadd__', 'remove', 'append', '__imul__'}
%HVLGHVPHWKRGV bytesDQG bytearrayDOVRVXSSRUWWKHXVXDO VHTXHQFHRSHUDWLRQVLQ7DEOHRQSDJHDQGbytearrayVXS SRUWVPXWDEOHVHTXHQFHRSHUDWLRQVLQ7DEOHRQSDJH6HH PRUH LQ £8QLFRGH 6WULQJV¤ RQ SDJH DQG £%XLOWLQ )XQF WLRQV¤RQSDJH
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38 | Python Pocket Reference
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atuple = tuple('spam')
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Type Conversions 7DEOHVDQGGHILQHFRPPRQEXLOWLQWRROVIRUFRQYHUWLQJ IURPRQHW\SHWRDQRWKHU 3\WKRQDOVRVXSSRUWVD long(S) WRORQJDQG`X`WRVWULQJFRQYHUWHUVUHPRYHGLQ3\WKRQ 7DEOH6HTXHQFHFRQYHUWHUV Converter
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a
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The Assignment Statement target = expression target1 = target2 = expression target1, target2 = expression1, expression2 target1 += expression target1, target2, ... = same-length-iterable (target1, target2, ...) = same-length-iterable [target1, target2, ...] = same-length-iterable target1, *target2, ... = matching–length-iterable
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Augmented assignment $VHWRIDGGLWLRQDODVVLJQPHQWVWDWHPHQWIRUPDWVOLVWHGLQ7D EOHDUHDYDLODEOH.QRZQDVDXJPHQWHGDVVLJQPHQWVWKHVH IRUPDWVLPSO\DELQDU\H[SUHVVLRQSOXVDQDVVLJQPHQW)RULQ VWDQFHWKHIROORZLQJWZRIRUPDWVDUHURXJKO\HTXLYDOHQW X = X + Y X += Y
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7DEOH$XJPHQWHGDVVLJQPHQWVWDWHPHQWV X += Y
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X > a, b, c, d = [1, 2, 3, 4] >>> a, d (1, 4) >>> for (a, b, c) in [[1, 2, 3], [4, 5, 6]]: ... print(a, b, c) ... 1 2 3 4 5 6
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The Expression Statement expression function([value, name=value, *name, **name...]) object.method([value, name=value, *name, **name...])
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(DFKvalueGHQRWHVDQREMHFWWREHSULQWHG7KLVFDOOLVFRQILJ XUHGE\LWVWKUHHNH\ZRUGRQO\DUJXPHQWV sepLVDVWULQJWRSODFHEHWZHHQYDOXHV GHIDXOWVWRDVSDFH ' ' endLVDVWULQJWRSODFHDWWKHHQGRIWKHWH[WSULQWHG GH IDXOWVWRDQHZOLQH '\n' fileLVWKHILOHOLNHREMHFWWRZKLFKWH[WLVZULWWHQ GHIDXOWV WRVWDQGDUGRXWSXW sys.stdout 3DVVHPSW\RUFXVWRPVWULQJVWRVXSSUHVVVSDFHVHSDUDWRUVDQG OLQHIHHGVDQGSDVVDILOHRUILOHOLNHREMHFWWRUHGLUHFWRXWSXW LQ\RXUVFULSW >>> print(2 ** 32, 'spam') 4294967296 spam >>> print(2 ** 32, 'spam', sep='') 4294967296spam >>> print(2 ** 32, 'spam', end=' '); print(1, 2, 3) 4294967296 spam 1 2 3 >>> print(2 ** 32, 'spam', sep='', file=open('out', 'w'))
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>>> open('out').read() '4294967296spam\n'
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Python 2.X print statements ,Q3\WKRQ;SULQWLQJLVDVSHFLILFVWDWHPHQWLQVWHDGRIDEXLOW LQIXQFWLRQRIWKHIROORZLQJIRUP print [value [, value]* [,]] print >> file [, value [, value]* [,]]
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Specific Statements | 61
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7KH3\WKRQ;printVWDWHPHQWFDQDOVRQDPHDQRSHQRXWSXW ILOHOLNHREMHFWWREHWKHWDUJHWRIWKHSULQWHGWH[WLQVWHDGRI sys.stdout fileobj = open('log', 'a') print >> fileobj, "Warning-bad spam!"
,IWKHILOHREMHFWLV None sys.stdoutLVXVHG7KLV3\WKRQ; >>V\QWD[LVHTXLYDOHQWWRWKHfile=FNH\ZRUGDUJXPHQWLQ3\ WKRQ 7KHUH LV QR HTXLYDOHQW WR sep=S LQ 3\WKRQ ¦V VWDWHPHQW 7RXVHWKH3\WKRQSULQWLQJIXQFWLRQLQ3\WKRQ;UXQWKH IROORZLQJ from __future__ import print_function
The if Statement if test: suite [elif test: suite]* [else: suite]
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The while Statement while test: suite [else: suite]
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The for Statement for target in iterable: suite [else: suite]
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The pass Statement pass
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The continue Statement continue
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64 | Python Pocket Reference
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7DEOH$UJXPHQWIRUPDWVLQGHILQLWLRQV Argument format
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Specific Statements | 65
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Python 3.0 function annotations 3\WKRQDOVRJHQHUDOL]HVIXQFWLRQGHILQLWLRQWRDOORZDUJX PHQWVDQGUHWXUQYDOXHVWREHDQQRWDWHGZLWKREMHFWYDOXHVIRU XVHLQH[WHQVLRQV$QQRWDWLRQVDUHFRGHGDV :valueDIWHUWKH DUJXPHQWQDPHDQGEHIRUHDGHIDXOWDQG->valueDIWHUWKHDU JXPHQWOLVW7KH\DUHFROOHFWHGLQWRDQ__annotations__DWWULE XWHEXWDUHQRWRWKHUZLVHWUHDWHGDVVSHFLDOE\3\WKRQLWVHOI >>> def f(a:99, b:'spam'=None) -> float: ... print(a, b) ... >>> f(88) 88 None >>> f.__annotations__ {'a': 99, 'b': 'spam', 'return': }
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Defaults and attributes 0XWDEOH GHIDXOW DUJXPHQW YDOXHV DUH HYDOXDWHG RQFH DW def VWDWHPHQWWLPHQRWRQHDFKFDOODQGVRFDQUHWDLQVWDWHEH WZHHQFDOOV+RZHYHUVRPHFRQVLGHUWKLVEHKDYLRUWREHDFDY HDWDQGFODVVHVDQGHQFORVLQJVFRSHUHIHUHQFHVDUHRIWHQEHWWHU VWDWHUHWHQWLRQWRROV XVHNoneGHIDXOWVIRUPXWDEOHDQGH[SOLFLW WHVWVWRDYRLGFKDQJHVDVVKRZQLQWKHIROORZLQJ¦VFRPPHQWV >>> def grow(a, b=[]): ... b.append(a) ... print(b)
66 | Python Pocket Reference
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... >>> grow(1); grow(2) [1] [1, 2]
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@C def f(): ...
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68 | Python Pocket Reference
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VWDWHPHQW 8VH D return VWDWHPHQW ZLWK QR YDOXH WR HQG WKH LWHUDWLRQRUVLPSO\IDOORIIWKHHQGRIWKHIXQFWLRQ def generateSquares(N): for i in range(N): yield i ** 2 >>> G = generateSquares(5) >>> list(G) [0, 1, 4, 9, 16]
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72 | Python Pocket Reference
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GeneratorExit
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NotImplementedError
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Built-in Exceptions | 127
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SystemExit
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5DLVHGRQ8QLFRGHUHODWHGHQFRGLQJRUGHFRGLQJHUURUV DVXSHUFODVVFDWHJRU\DQGDVXEFODVVRIValueError UnicodeEncodeError UnicodeDecodeError UnicodeTranslateError
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128 | Python Pocket Reference
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ValueError
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7KHVXSHUFODVVIRUDOORIWKHIROORZLQJZDUQLQJFDWHJRULHV LWLVDGLUHFWVXEFODVVRIException UserWarning
:DUQLQJVJHQHUDWHGE\XVHUFRGH DeprecationWarning
:DUQLQJVDERXWGHSUHFDWHGIHDWXUHV PendingDeprecationWarning
:DUQLQJV DERXW IHDWXUHV WKDW ZLOO EH GHSUHFDWHG LQ WKH IXWXUH SyntaxWarning
:DUQLQJVDERXWGXELRXVV\QWD[ RuntimeWarning
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Built-in Exceptions | 129
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UnicodeWarning
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Warnings Framework :DUQLQJV DUH LVVXHG ZKHQ IXWXUH ODQJXDJH FKDQJHV PLJKW EUHDNH[LVWLQJFRGHLQDIXWXUH3\WKRQUHOHDVH¢DQGLQRWKHU FRQWH[WV:DUQLQJVPD\EHFRQILJXUHGWRSULQWPHVVDJHVUDLVH H[FHSWLRQV RU EH LJQRUHG 7KH ZDUQLQJV IUDPHZRUN FDQ EH XVHGWRLVVXHZDUQLQJVE\FDOOLQJWKHwarnings.warnIXQFWLRQ warnings.warn("feature obsolete", DeprecationWarning)
,QDGGLWLRQ\RXFDQDGGILOWHUVWRGLVDEOHFHUWDLQZDUQLQJV>> import re >>> patt = re.compile('hello[ \t]*(.*)') >>> mobj = patt.match('hello world!') >>> mobj.group(1) 'world!'
The re Pattern-Matching Module | 159
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,Q7DEOH &LVDQ\FKDUDFWHU5LVDQ\UHJXODUH[SUHVVLRQIRUP LQWKHOHIWFROXPQRIWKHWDEOHDQGPDQGQDUHLQWHJHUV(DFK IRUPXVXDOO\FRQVXPHVDVPXFKRIWKHVWULQJEHLQJPDWFKHGDV SRVVLEOHH[FHSWIRUWKHQRQJUHHG\IRUPV ZKLFKFRQVXPHDV OLWWOHDVSRVVLEOHDVORQJDVWKHHQWLUHSDWWHUQVWLOOPDWFKHVWKH WDUJHWVWULQJ 7DEOH 5HJXODUH[SUHVVLRQSDWWHUQV\QWD[ Form
Description
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^
Matches start of string (of every line in MULTILINE mode).
$
Matches end of string (of every line in MULTILINE mode).
C
Any nonspecial character matches itself.
R*
Zero or more occurrences of preceding regular expression R (as many as possible).
R+
One or more occurrences of preceding regular expression R (as many as possible).
R?
Zero or one occurrence of preceding regular expression R.
R{m}
Matches exactly m repetitions of preceding regular expression R.
R{m,n}
Matches from m to n repetitions of preceding regular expression R.
R*?, R+?, R??, R{m,n}?
Same as *, +, and ?, but matches as few characters/times as possible; nongreedy.
[...]
Defines character set; e.g., [a-zA-Z] matches all letters (also see Table 20).
160 | Python Pocket Reference
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Form
Description
[^...]
Defines complemented character set: matches if character is not in set.
\
Escapes special characters (e.g., *?+|()) and introduces special sequences (see Table 20). Due to Python rules, write as \\ or r'\\'.
\\
Matches a literal \; due to Python string rules, write as \\\\ in pattern, or r'\\'.
\number
Matches the contents of the group of the same number: (.+) \1 matches “42 42”
R|R
Alternative: matches left or right R.
RR
Concatenation: matches both Rs.
(R)
Matches any RE inside (), and delimits a group (retains matched substring).
(?: R)
Same as (R) but doesn’t delimit a group.
(?= R)
Look-ahead assertion: matches if R matches next, but doesn’t consume any of the string (e.g., X (?=Y) matches X if followed by Y).
(?! R)
Negative look-ahead assertion: matches if R doesn’t match next. Negative of (?=R).
(?P R)
Matches any RE inside () and delimits a named group (e.g., r'(?P[a-zA-Z_]\ w*)' defines a group named id).
The re Pattern-Matching Module | 161
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Form
Description
(?P=name)
Matches whatever text was matched by the earlier group named name.
(?#...)
A comment; ignored.
(?letter)
letter is one of a, i, L, m, s, x, or u. Set flag (re.A, re.I, re.L, etc.) for entire RE.
(?if', 1, 2.0)) 8 >>> open('data', 'rb').read() b'\x00\x00\x00\x01@\x00\x00\x00' >>> struct.unpack('>if', open('data', 'rb').read()) (1, 2.0)
Python Portable SQL Database API 3\WKRQ¦VSRUWDEOH64/GDWDEDVH$3,SURYLGHVVFULSWSRUWDELOLW\ EHWZHHQGLIIHUHQWYHQGRUVSHFLILF64/GDWDEDVHSDFNDJHV)RU HDFKYHQGRULQVWDOOWKHYHQGRUVSHFLILFH[WHQVLRQPRGXOHEXW ZULWH\RXUVFULSWVDFFRUGLQJWRWKHSRUWDEOHGDWDEDVH$3,>> from sqlite3 import connect >>> conn = connect(r'C:\users\mark\misc\temp.db') >>> curs = conn.cursor() >>> >>> >>> >>>
curs.execute('create table jobs (name, title, pay)') prefix = 'insert into jobs values ' curs.execute(prefix + "('Bob', 'dev', 100)") curs.execute(prefix + "('Sue', 'dev', 120)")
>>> curs.execute("select * from jobs where pay > 100") >>> for (name, title, pay) in curs.fetchall(): ... print(name, title, pay) ... Sue dev 120 >>> curs.execute("select name, pay from jobs").fetchall() [('Bob', 100), ('Sue', 120)] >>> query = "select * from jobs where title = ?" >>> curs.execute(query, ('dev',)).fetchall() [('Bob', 'dev', 100), ('Sue', 'dev', 120)]
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Connection Objects &RQQHFWLRQREMHFWVUHVSRQGWRWKHIROORZLQJPHWKRGV close()
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&DOOVDVWRUHGGDWDEDVHSURFHGXUHZLWKWKHJLYHQQDPH 7KHVHTXHQFHRISDUDPHWHUVPXVWFRQWDLQRQHHQWU\IRU HDFK DUJXPHQW WKDW WKH SURFHGXUH H[SHFWV UHVXOW LV UH WXUQHGDVDPRGLILHGFRS\RIWKHLQSXWV
Python Portable SQL Database API | 181
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close()
&ORVHV WKH FXUVRU QRZ UDWKHU WKDQ ZKHQ __del__ LV FDOOHG execute(operation [,parameters])
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)HWFKHVWKHQH[WURZRIDTXHU\UHVXOWVHWUHWXUQLQJDVLQ JOHVHTXHQFHRUNoneZKHQQRPRUHGDWDLVDYDLODEOH fetchmany([size=cursor.arraysize])
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182 | Python Pocket Reference
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Core Language Hints S[:]PDNHVDWRSOHYHO VKDOORZ FRS\RIDQ\VHTXHQFH copy.deepcopy(X) PDNHV IXOO FRSLHV list(L) DQG D.copy()FRS\OLVWVDQGGLFWLRQDULHV L[:0]=[X,Y,Z]LQVHUWVLWHPVDWIURQWRIOLVWLLQSODFH L[len(L):]=[X,Y,Z] L.extend([X,Y,Z]) DQG L += [X,Y,Z] DOO LQVHUW PXOWLSOH LWHPV DW WKH HQG RI D OLVW LQSODFH L.append(X)DQGX=L.pop()FDQEHXVHGWRLPSOHPHQWLQ SODFHVWDFNRSHUDWLRQVZKHUHWKHHQGRIWKHOLVWLVWKHWRS RIWKHVWDFN 8VHfor key in D.keys():WRLWHUDWHWKURXJKGLFWLRQDULHV RUVLPSO\for key in D:LQYHUVLRQDQGODWHU,Q3\WKRQ WKHVHWZRIRUPVDUHHTXLYDOHQWVLQFHkeysLVDQLWHUDEOH YLHZ 8VHfor key in sorted(D):WRLWHUDWHRYHUGLFWLRQDU\NH\V LQ VRUWHG IDVKLRQ LQ YHUVLRQ DQG ODWHU WKH IRUP K=D.keys(); K.sort(); for key in K: DOVR ZRUNV LQ 3\WKRQ;EXWQRW3\WKRQVLQFHkeysUHVXOWVDUHYLHZ REMHFWVQRWOLVWV X=A or B or NoneDVVLJQVXWRWKHILUVWWUXHREMHFWDPRQJ ADQGBRUNoneLIERWKDUHIDOVH LHRUHPSW\ X,Y = Y,XVZDSVWKHYDOXHVRIXDQGY red, green, blue = range(3)DVVLJQVLQWHJHUVHULHV 8VH try/finallyVWDWHPHQWVWRHQVXUHWKDWDUELWUDU\WHU PLQDWLRQ FRGH LV UXQ HVSHFLDOO\ XVHIXO DURXQG ORFNLQJ FDOOV DFTXLUHEHIRUHWKHtryUHOHDVHLQWKHfinally Python Idioms and Hints | 183
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Environment Hints 8VH if __name__ == '__main__':WRDGGVHOIWHVWFRGHRU DFDOOWRDPDLQIXQFWLRQDWWKHERWWRPRIPRGXOHILOHV WUXHRQO\ZKHQILOHLVUXQQRWZKHQLWLVLPSRUWHGDVD OLEUDU\FRPSRQHQW 7R ORDG ILOH FRQWHQWV LQ D VLQJOH H[SUHVVLRQ XVH data=open('filename').read() 7R LWHUDWH WKURXJK WH[W ILOHV E\ OLQHV XVH for line in file:LQYHUVLRQDQGODWHU LQROGHUYHUVLRQVXVH for line in file.readlines(): 7RUHWULHYHFRPPDQGOLQHDUJXPHQWVXVHsys.argv 7RUHWULHYHVKHOOHQYLURQPHQWVHWWLQJVXVHos.environ 7KH VWDQGDUG VWUHDPV DUH sys.stdin sys.stdout DQG sys.stderror 7R UHWXUQ D OLVW RI ILOHV PDWFKLQJ D JLYHQ SDWWHUQ XVH glob.glob('pattern') 7RUHWXUQDOLVWRIILOHVDQGVXEGLUHFWRULHVRQDSDWKXVH os.listdir('.') 7RZDONDQHQWLUHWUHHRIGLUHFWRULHVXVHos.walkLQ3\WKRQ DQG os.path.walkLVDOVRDYDLODEOHLQ3\WKRQ RQO\ 7R UXQ VKHOO FRPPDQGVZLWKLQ3\WKRQVFULSWV\RX FDQ XVH os.system('cmdline') output=os.popen('cmdline', 'r').read()7KHODWWHUIRUPUHDGVWKHVSDZQHGSURJUDP¦V VWDQGDUG RXWSXW DQG PD\ DOVR EH XVHG WR UHDG OLQHE\OLQH 184 | Python Pocket Reference
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2WKHUVWUHDPVRIDVSDZQHGFRPPDQGDUHDYDLODEOHYLD WKH subprocess PRGXOH LQ 3\WKRQ DQG WKH os.popen2/3/4 FDOOV LQ 3\WKRQ ; RQO\ 7KH os.fork/ os.exec*FDOOVKDYHVLPLODUHIIHFWRQ8QL[OLNHSODWIRUPV 7RPDNHDILOHDQH[HFXWDEOHVFULSWRQ8QL[OLNHSODWIRUPV DGG D OLQH OLNH #!/usr/bin/env python RU #!/usr/local/ bin/pythonDWWKHWRSDQGJLYHWKHILOHH[HFXWDEOHSHUPLV VLRQVZLWKD chmodFRPPDQG2Q:LQGRZVILOHVFDQEH FOLFNHGDQGUXQGLUHFWO\GXHWRWKHUHJLVWU\ 7KHdir([object])IXQFWLRQLVXVHIXOIRULQVSHFWLQJDWWULE XWH QDPHVSDFHV print(object.__doc__) RIWHQ JLYHV GRFXPHQWDWLRQ 7KHhelp([object])IXQFWLRQSURYLGHVLQWHUDFWLYHKHOSIRU PRGXOHVIXQFWLRQVW\SHVDQGPRUH help(str)JLYHVKHOS RQ WKH str W\SH help("module") JLYHV KHOS RQ PRGXOHV HYHQ LI WKH\ KDYH QRW \HW EHHQ LPSRUWHG DQG help("topic")JLYHVKHOSRQNH\ZRUGVDQGRWKHUKHOSWRS LFV XVH"topics"IRUDOLVWRIKHOSWRSLFV print()DQGinput() NQRZQDVprintDQGraw_input()LQ 3\WKRQ; XVHsys.stdoutDQGsys.stdinVWUHDPV DVVLJQ WR ILOHOLNH REMHFWV WR UHGLUHFW ,2 LQWHUQDOO\ RU XVH WKH print(..., file=F)IRUPLQ3\WKRQ RUWKH print >> F, ...IRUPLQ3\WKRQ;
Usage Hints 8VHfrom __future__ importfeaturenameWRHQDEOHH[SHU LPHQWDOODQJXDJHIHDWXUHVWKDWPLJKWEUHDNH[LVWLQJFRGH ,QWXLWLRQDERXWSHUIRUPDQFHLQ3\WKRQSURJUDPVLVXVX DOO\ZURQJ DOZD\VPHDVXUHEHIRUHRSWLPL]LQJRUPLJUDW LQJWR&8VHWKH profileDQG timePRGXOHV DVZHOODV F3URILOHDQGWLPHLW 6HHPRGXOHVunittest DND3\8QLW DQGdoctestIRUDX WRPDWHGWHVWLQJWRROVVKLSSHGZLWKWKH3\WKRQVWDQGDUG OLEUDU\ unittestLVDFODVVIUDPHZRUN doctestVFDQVGRF XPHQWDWLRQVWULQJVIRUWHVWVDQGRXWSXWV Python Idioms and Hints | 185
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186 | Python Pocket Reference
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