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Python 2.7 Quick Reference Sheet
ver 2.01 ʹ 110105 (sjd)
Interactive Help in Python Shell help() Invoke interactive help help( m ) Display help for module m help( f ) Display help for function f dir( m ) Display names in module m
Small Operator Precedence Table func_name ( args, ͙ ) Function call x [ index : index ] Slicing x [ index ] Indexing x.attribute Attribute reference ** Exponentiation *, /, % Multiply, divide, mod +, -‐ Add, subtract
, <, <=, >=, !=, == Comparison in, not in Membership tests not, and, or Boolean operators NOT, AND, OR
Module Import import module_name from module_name import name , ͙ from module_name import *
Common Data Types Type Description Literal Ex
int long float complex bool str tuple list dict
32-‐bit Integer Integer > 32 bits Floating point number Complex number Boolean Character sequence Immutable sequence Mutable sequence Mapping
101L
1.2J
True, False ͞ Python͟ (2, 4, 7) [2, x, 3.1] { x:2, y:5 }
Common Syntax Structures Assignment Statement var = exp Console Input/Output var = input( [ prompt ] ) var = raw_input( [ prompt ] ) print exp [,] ͙ Selection if ( boolean_exp ): stmt ͙ [elif ( boolean_exp ): stmt ͙ ] ͙ [else: stmt ͙ ] Repetition while ( boolean_exp ): stmt ͙ Traversal for var in traversable_object : stmt ͙ Function Definition def function_name ( parmameters ): stmt ͙ Function Call function_name ( arguments ) Class Definition class Class_name [ ( super_class ) ]: [ class variables ] def method_name ( self, parameters ): stmt Object Instantiation obj_ref = Class_name ( arguments ) Method Invocation obj_ref.method_name ( arguments ) Exception Handling try: stmt ͙ except [ exception_type ] [, var ]: stmt ͙
Common Built-‐in Functions Function Returns abs( x ) Absolute value of x dict() Empty dictionary, eg: d = dict() float( x ) int or string x as float id( obj ) memory addr of obj int ( x ) float or string x as int len( s ) Number of items in sequence s list() Empty list, eg: m = list() max( s ) Maximum value of items in s min( s ) Minimum value of items in s open( f ) Open filename f for input ord( c ) ASCII code of c pow( x,y ) x ** y range( x ) A list of x ints 0 to x -‐ 1 round( x,n ) float x rounded to n places str( obj ) str representation of obj sum( s ) Sum of numeric sequence s tuple( items ) tuple of items type( obj ) Data type of obj
Common Math Module Functions Function Returns (all float) ceil( x ) Smallest whole nbr >= x cos( x ) Cosine of x radians degrees( x ) x radians in degrees radians( x ) x degrees in radians exp( x ) e ** x floor( x ) Largest whole nbr <= x hypot( x, y ) sqrt( x * x + y * y ) log( x [, base ]) Log of x to base or natural log if base not given pow( x, y ) x ** y sin( x ) Sine of x radians sqrt( x ) Positive square root of x tan( x ) Tangent of x radians pi Math constant pi to 15 sig figs e Math constant e to 15 sig figs
Common String Methods
S .method() Returns (str unless noted)
capitalize S with first char uppercase center( w ) S centered in str w chars wide count( sub ) int nbr of non-‐overlapping occurrences of sub in S find( sub ) int index of first occurrence of sub in S or -‐1 if not found isdigit() bool True if S is all digit chars, False otherwise islower() isupper()
bool True if S is all lower/upper case chars, False otherwise join( seq ) All items in seq concatenated into a str, delimited by S lower() upper()
Lower/upper case copy of S
lstrip() rstrip()
Copy of S with leading/ trailing whitespace removed, or both split([ sep ]) List of tokens in S , delimited by sep ; if sep not given, delimiter is any whitespace
Formatting Numbers as Strings
Syntax: ͞ format_spec ͟ % numeric_exp format_spec syntax: % width.precision type
x width (optional): align in number of colums specified; negative to left-‐align, precede with 0 to zero-‐fill x precision (optional): show specified digits of precision for floats; 6 is default x type (required): d (decimal int), f (float), s (string), e (float ʹ exponential notation) x Examples for x = 123, y = 456. ͞йϲĚ͟ % x -‐>... 123 ͞йϬϲĚ͟ % x -‐> 000123 ͞ %8.2f % y -‐>.. 456. ͞ϴ͘ϮĞ͟ йLJ -‐> 4.57e+ ͞ -‐8s͟й͞ ,ĞůůŽ͟ -‐> Hello...
Common List Methods L .method() Result/Returns append( obj ) Append obj to end of L count( obj ) Returns int nbr of occurrences of obj in L index( obj ) Returns index of first occurrence of obj in L ; raises ValueError if obj not in L pop([ index ]) Returns item at specified index or item at end of L if index not given; raises IndexError if L is empty or index is out of range remove( obj ) Removes first occurrence of obj from L ; raises ValueError if obj is not in L reverse() Reverses L in place sort() Sorts L in place
Common Tuple Methods T .method() Returns count( obj ) Returns nbr of occurrences of obj in T index( obj ) Returns index of first occurrence of obj in T ; raises ValueError if obj is not in T
Common Dictionary Methods D .method() Result/Returns clear() Remove all items from D get( k [, val ]) Return D [ k ] if k in D , else val has_key( k ) Return True if k in D , else False items() Return list of key-‐value pairs in D ; each list item is 2-‐item tuple keys() Return list of D ͛ƐŬĞLJƐ pop( k , [ val ]) Remove key k , return mapped value or val if k not in D values() Return list of D ͛s values
Common File Methods F .method() Result/Returns read([ n ]) Return str of next n chars from F , or up to EOF if n not given readline([ n ]) Return str up to next newline, or at most n chars if specified readlines() Return list of all lines in F , where each item is a line write( s ) Write str s to F writelines( L ) Write all str in seq L to F close() Closes the file
Other Syntax Hold window for user keystroke to close: raw_input(͞ Press to quit.͟ ) Prevent execution on import: ŝĨͺͺŶĂŵĞͺͺсс͞ͺͺŵĂŝŶͺͺ͗͟ main()
Displayable ASCII Characters 32 SP 48 0 64 @ 80 P 96 ` 112 p 33! 49 1 65 A 81 Q 97 a 113 q 34 ͞ 50 2 66 B 82 R 98 b 114 r 35 # 51 3 67 C 83 S 99 c 115 s 36 $ 52 4 68 D 84 T 100 d 116 t 37 % 53 5 69 E 85 U 101 e 117 u 38 & 54 6 70 F 86 V 102 f 118 v 39 ͚ 55 7 71 G 87 W 103 g 119 w 40 ( 56 8 72 H 88 X 104 h 120 x 41 ) 57 9 73 I 89 Y 105 i 121 y 42 * 58 : 74 J 90 Z 105 j 122 z 43 + 59 ; 75 K 91 [ 107 k 123 { 44 , 60 < 76 L 92 \ 108 l 124 | 45 -‐ 61 = 77 M 93 ] 109 m 125 }
- 62 > 78 N 94 ^ 110 n 126 ~ 47 / 63? 79 O 95 _ 111 o 127 DEL μ\¶ μ\W¶ μ\n¶ = 10
