Python Cheatsheet

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Change log

2014-08-25 :: Python conversion to HTML version
2014-08-11 :: Makefile for python cheatsheet
2014-08-11 :: Few typo corrections, added os.stat
2014-07-31 :: Python cheatsheet, first public preview
2013-05-12 :: Python cheat-cheat improvements
2013-04-04 :: Created template for Python cheat sheet

Python 2.7.x

Set of interpreter: #!/usr/bin/env python
Comments: # everything behind hash
""" more lines comment """

Command line parameters

python options script.py – run script filename
-V – print version
-c 'code' – run code from command line

Expression statements

FOR cycle	WHILE contition
for identifier in list : ␣␣␣␣list-processing code [ else : ␣␣␣␣suite ]	while condition ␣␣␣␣repeat if condition is true [ else: ␣␣␣␣suite ]
IF-THEN-ELSE	TRY block
if condition : ␣␣␣␣true suite [ elif condition: ␣␣␣␣else if true ] [ else : ␣␣␣␣else suite ]	try: ␣␣␣␣possible runtime error except [type [as value]]: ␣␣␣␣error-recovery code [ else: ␣␣␣␣suite ] [ finally: ␣␣␣␣suite ]

import module – find and initialize module
module.function() – use function of imported module
from module import * – import all stuff to local name space
import module as name – rename imported module
from module import name as othername
break – exit while or for loop, skip associated else
continue – perform next iteration of cycle
global name – reference global value
exec("print 'Ahoj'") – compile and exec code
with expression [as variable]: ␣␣␣␣suite – block entry actions
pass – do-nothing placeholder statement
del name, del name[i], del name[i:j:k], del name.attibute – delete variables, items, keys, attributes
assert expression [, message]
exec codestring

Classes

class Name:

suite

_private – underscored named object is private
def __init__(self, ...):

self.data = []

class DerivedClass(BaseClass) – inheritance
def __iter__(self): –

Functions

def function(param1, param2,...):
def func(arg,... arg=value, ... *arg, **arg):

arg – matched by name or position
arg=value – default value if arg is not passed
*arg – collect extra positional args as a new tuple
**arg – collect extra positional args as a new dictionary

lambda args1 : expression – anonymous function maker
return [expression] – return from function
yield expression – suspend function state and return, on next iteration restore prior state

Variables

variable = 12 – assign value
type(variable) – return type of variable
global name [,name] – global variable in local context
Number formats:

2006, 2006l, 2006L – decimal integer, long;
0775, oct(0x1fd) – octal;
0xBABE, hex(47806) – hexadecimal;
0b101010, bin(42) – binary;
3.14, 314e-2 – floating point;
1+2j, 1.0+2.0J, complex(1,2) – complex number;
b'Ahoj' – sequence of 8-bit values;

int(x), long(x), float(x), str(n) – type conversions
c=1+2j; c.conjugate(), (1+2j).conjugate() – conjugate of complex number 1-2j
abs(x) – absolute value of x
round(x[,n]) – x rounded to n digits
(10.5).as_integer_ratio() – returns tuple (21, 2)
(255).bit_length() – number of digits of binary
X, Y = Y, X – swap values of X and Y
a,b,c = range(3) – read list values, a=0,b=1,c=2
vars(), globals(), locals() – return dictionary of variables
setattr(obj, 'b', c) is equivalent obj.b = c
getattr(obj, 'a') is equivalent obj.a
hasattr(obj, name) – True if name is object atribute

Constants

False, True – boolean
None – represents no value
bool([X]) – returns boolean value of object X.

Operators

or, and, not x – boolean operators
| (or), ^ (xor), & (and), ~x (neg.) – binary operators
X in Y, X not in Y – membership tests
X is Y, X is not Y – same or different object
<, <=, >, >=, <>, !=, == – comparisons
*, /, //, % – multiply, divide, floor divide, remainder
x << n, x >> n – bitwise shifts by n bits
x**y, pow(x,y) – power x^y
+= &= -= |= *= ^= /= >>= %= <<= **= //=
divmod(x,y) – return tuple (x/y, x%y)

Data types

Function	Tuple	List	Dict.	String	Set
Init.	`()`,`tuple()`	`[]`, `list()`	, `dict()`	`""`,`''`,`str()`	`set()`
`clear`	—	—	●	—	●
`copy`	—	—	●	—	●
`count`	●	●	—	●	—
`index`	●	●	—	●	—
`pop`	—	●	●	—	●
`remove`	—	●	—	—	●
`update`	—	—	●	—	●

Tuples

t = (), t = tuple() – create empty tuple
t = (1, 2, 3) – like list, but can't change their values
t[1] – access second item, returns 2
t.index(x [, i [, j]]) – return index of first occurrence of x
t.count(x) – return number of item x

Lists

l = [], l = list() – empty list
l = [1, 2, 3] – one dimensional array
l[1] – returns 2, indexing: 1₀ 2₁ 3₂
l[i:j] – slicing from index i to j
l[i:] – slicing from index i to end of list
l[i:j:k] – slicing with step k ≈ pprox l[slice(i,j[,k])]
l[-1] – last item (first from back)
0 in [1, 2, 3] – False, 1 in [1, 2, 3] True
l = range(5) – create list [0, 1, 2, 3, 4]
l = range(start, stop[, step]) – given range with step
l = [x**2 for x in range(9)] – list from expression result
l.index(item) – return index of item in list
l.count(item) – total number of occurrences of item
l = ["text", 12, 3, [1, 2]] – more types in one list
l2d=[[1,2,3], [4,5,6], [7,8,9]] – two-dimensional list
l2d[1][1] – returns 5
list('abc') – returns list of chars ['a','b','c']
len(l) – return length of list
l.append(value) – add value to the list
l.extend([4,5]), list[len(list):]=[4,5], list += [4,5] – append another list
l.insert(i, x), list[i]=x – insert x at given index
l[:0]=[x,y,z] – insert item at front of list
l.remove(value) – remove first occurrence of value
l.pop(i), l.pop() – return and remove value, without index last
l.index(x [, i[, j]]) – index of first occur. of x, between i to j
l.count(x) – return number of occurrence of object x
l.sort(key=None, reverse=False) – sort list in-place
l.reverse() – reverse list in-place
sum(l) – return sum of numeric list

Dictionaries

h = {}, h = dict() – initialization of empty dictionary
h = { "key1": "value", "key2": "another"} – definition
h = dict(key1="value", key2="another") – different syntax
h["key3"] = 333 – add another value
h = {c: ord(c) for c in 'spam'} – comprehension expression
h.has_key("key") – returns True if key exist
h.keys() – return list of keys
h.values() – return list of values
h.clear() – remove all items
g = h.copy() – returns a shallow copy of h
h.get(key [, default]) – if key is not found return default
h.popitem() – removes and returns an (key, value) pair
h.pop(k [, def]) – returns and removes k else return def
h.fromkeys(seq [, value]) – new dictionary from keys in seq
dict(zip(['a','b'], [1,2])) – join to {'a': 1, 'b': 2}

Sets

A = set() – empty set A={ ∅ }
A = set('Ouagadougou') – A = set(['a','d','g','o','u','O']), unordered collection of unique and immutable objects
A = {'a', 'd', 'g', 'o', 'u', 'O'} – set definition
A = frozenset(range(−5, 5)) – immutable set of -5…4
'a' in A – returns True if value is presented a ∈ A
A - B, A.difference(B) – new set contains difference A \ B
A | B, A.union(B) – join two sets, no duplicates A ⋃ B
A & B, A.intersection(B) – same items in both sets A ⋂ B
A <= B, A.issubset(B) – returns True is A is subset of B A ⊂ B
A >= B, A.issuperset(B) – is A superset of B? A ⊃ B
A < B, A > B – true subset, superset A ⊂ B, A ⊃ B
A ^ B, A.symmetric_difference(B) – A ∆ B = (A ⋃ B) \ (A ⋂ B)
A |= B, A.update(B) – adds items in B to A
A.discard(X) – remove item if exist
A.add(X), A.remove(X) – add, remove item from set
A.clear() – remove all items
A.pop() – remove and return arbitrary item
len(A) – get number of items in A
for x in A: – all iteration context
B=A.copy(), B=set(A) – make copy of set

Strings

s = "Hello", s = 'Hello' – definition, " and ' works same
"""This is multi-line block""" – collects into a single string
s[1]='e' – indexing H₀ e₁ l₂ l₃ o₄
str(n) – convert number n to string
'Hello ' + 'World', "Hello" "World" – concatenation
'Hello' * 3 – repetition 3×
Unicode α: u"\03b1", U"\U000003B1", u"\N{GREEK SMALL LETTER ALPHA}"
Raw string: r"\n", R'\n' does not interpret escape sequences
Unicode raw string: ur"\n", UR'\n'
str(), bytes(), bytearray() – create string from object
\xhh, \ooo, \0 – hex, octal, null byte
chr(65), unichr(65), ord('A') – returns character, ASCII code
eval(s) – convert and execute code given by string
execfile(filename) – like eval, but for whole file

Output and formating

print(*objects, sep=' ', end='\n', file=sys.stdout)
'%s, %s, %.2f' % (13, 'txt', 22/7.0) – '13, txt, 3.14'
'{0}, {1}, {2:.2f}'.format(13,'txt',22/7.0) – other def.
"%(a)d %(b)s" % {"a":6, "b":"text"} – formating dictionary
"{a} {b}".format(**{'a':1, 'b':2}) – formating dictionary
"%*s" % (10, "text") – width given as parameter
"%#x %#o" % (15,15) – prints number base prefixes
"%+.*f" % (5, 22.0/7) – +3.14286, 5 digits after ‘.’
%[(keyname)][flags][width][.precision]typecode
Flags: -/+ left/right justify, 0/' ' zero/space fill
String formating typecodes:

s – String (or any object, uses str())
r, – s, but uses repr(), not str()
c – Character (int or str)
d, i, u – Decimal (base 10 integer)
o – Octal (base 8 integer)
x, X – Hex (base 16 integer)
e, E – Floating-point exponent
f, F – Floating-point decimal
g, G – Floating-point e,f/E,f
%% – Literal '%'

{fieldname!conversionflag:formatspec
[[fill]align][sign][#][0][width][,][.prec][typecode]

String methods

s.find/rfind(sub, [,s [,e]]) – index of first occur. of sub,
s.index/rindex(sub [,s [,e]]) – ValueError if not found
s.endswith/startwith(sub [,s [,e]]) – true if starts/ends
s.count(sub, [,s [,e]]) – get number of substrings
s.upper(), s.lower(), s.swapcase() – converts case
s.split([sep [, maxsplit]) – return list of words
sep.join(iterable) – concatenates with separator
' and '.join(['a', 'b', 'c']) – returns 'a and b and c'
s.replace(old, new [, count]) – replace old by new
s.splitlines(0/1) – split by '\n', 1 – keeps end char
s.strip([chars]) – remove leading and trailing white spaces
s.lstrip, s.rstrip – just from left or right side
s.center/ljust/rjust(width [,fill]) – justify string
s.capitalize() / s.title() – make first/all word(s) uppercase
s.expandtabs(tabsize) – replaces tabs with spaces (default 8)
isalnum, isalpha, isdecimal, isdigit, isidentifier, islower, isnumeric, isprintable, isspace, istitle, isupper – tests

Other build-in functions

max(iterable), min(iterable) – return max/min value
reversed(iterable) – return a reverse iterator
sorted(iterable, key=None, reverse=False) – return sorted
enumerate(iterable, start=0) – return an enumerate object
all(iter), any(iter) – True if all/any of elements are/is true.
hash(obj) – return hash value of object
iter(o [,sentinel]) – return an iterator object
next(iterator [,default]) – return next item from iterator
map(function, iterable, ...) – apply function on every item
input([prompt]) – read line for stdin

Work with files

file=open('data.txt'[, 'mode']) – open, mode: r,w,rb,w,r+,w+
s = file.read([n]) – read file of n bytes into string s
file.readline() – return line of file, empty at EOF
file.readlines() – read entire file into a list of line strings
for line in file: – process file line by line
file.write(s) – write string s into file
print >>file, "Output" – write string to file
file.writeline(list) – write all strings in list to file
file.close() – close to free resources
file.tell() – return file position
file.seek(offset [, whence]) – set file position
file.flush() – flushes file's buffer
file.truncate([size]) – truncate file to size bytes
file.fileno() – get file descriptor integer
file.closed, file.mode, file.name – return attributes

Regular expressions `(import re)`

ro=re.compile(pattern, flags=0) – create RegexObject ‘ro’
Flags: re.DOTALL (S), re.IGNORECASE (I), re.LOCALE (L), re.MULTILINE (M), re.VERBOSE (X), re.UNICODE (U)
re.match(pattern, string) – if match return MatchObject
re.search(pattern, string) – match regex anywhere in string
re.split(pattern,string) – split pattern
re.findall(pattern, string) – return substrings as list
re.finditer(pattern, string) – return matches as iterator
re.sub(pattern, repl, string, count=0, flags=0) – return string with replaced pattern
re.subn(…) – return tuple (string, num. of replacements)
re.escape(string) – string with escaped regex's metacharacters
RegexObject methods: ro.match, search, split, sub, subn, findall, finditer
ro.flags, ro.pattern – used argument for reg. obj. creation
ro.groups() – number of matched groups
ro.group(n) – return n^th string matched by regex
ro.start(), ro.end(), ro.span() – return starting, ending position or tuple

System specific functions and parameters

sys.argv – CLI parameters, argv[0] name of script
sys.stdin.readline() – read line from standard input
subprocess.call(["ls", "-l"]) – execute system command
out = subprocess.check_output(['uname', '-a']) – store output of command to variable
filelist = subprocess.Popen("ls *", shell=True, stdout=subprocess.PIPE).communicate()[0] – read data from pipe
os.stat('/path/to/file.txt') – return POSIX stat file info

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BruXy.REGNET.CZ

Python Cheatsheet

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Change log

Python 2.7.x

Command line parameters

Expression statements

Classes

Functions

Variables

Constants

Operators

Data types

Tuples

Lists

Dictionaries

Sets

Strings

Output and formating

String methods

Other build-in functions

Work with files

Regular expressions (import re)

System specific functions and parameters

Regular expressions `(import re)`