Essential Python Cheat Sheet

A Programming › Python cheat sheet in English by sschaub

A brief Python language reference for Python 2.6+ / 3.0+.

Python Functions String Conversion Statement Boolean Tuple

125,077 views 43,347 downloads 21 May 2012 History

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Data Types

Integer	-256, 15
Float	-253.23, 1.253e-10
String	"Hello", 'Goodbye', """Multiline"""
Boolean	True, False
List	[ value, ... ]
Tuple	( value, ... )¹
Dictionary	{ key: value, ... }
Set	{ value, value, ... }²

¹ Parentheses usually optional
² Create an empty set with set()

Statements

If Statement
if expression:
statements
elif expression:
statements
else:
statements

While Loop
while expression:
statements

For Loop
for var in collection:
statements

Counting For Loop
for i in range(start, end [, step]):
statements
(start is included; end is not)

Arithmetic Operators

x + y	add	x - y	subtract
x * y	multiply	x / y	divide
x % y	modulus	x ** y	x^y

Assignment shortcuts: x op= y
Example: x += 1 increments x

Comparison Operators

x< y	Less	x <= y	Less or eq
x > y	Greater	x >= y	Greater or eq
x == y	Equal	x != y	Not equal

Boolean Operators

not x

x and y

x or y

Exception Handling

try:
statements
except [ exception type [ as var ] ]:
statements
finally:
statements

Conversion Functions

int(expr)	Converts expr to integer
float(expr)	Converts expr to float
str(expr)	Converts expr to string
chr(num)	ASCII char num

String / List / Tuple Operations

len(s)	length of s
s[i]	ith item in s (0-based)
s[start : end]	slice of s from start (included) to end (excluded)
x in s	True if x is contained in s
x not in s	True if x is not contained in s
s + t	the concatenation of s with t
s * n	n copies of s concatenated
sorted(s)	a sorted copy of s
s.index(item)	position in s of item

More String Operations

s.lower()	lowercase copy of s
s.replace(old, new)	copy of s with old replaced with new
s.split( delim )	list of substrings delimited by delim
s.strip()	copy of s with whitespace trimmed
s.upper()	uppercase copy of s

Mutating List Operations

del lst[i]	Deletes ith item from lst
lst.append(e)	Appends e to lst
lst.insert(i, e)	Inserts e before ith item in lst
lst.sort()	Sorts lst

Dictionary Operations

len(d)	Number of items in d
del d[key]	Removes key from d
key in d	True if d contains key
d.keys()	Returns a list of keys in d

Function Definitions

def name(arg1, arg2, ...):
statements
return expr

Environment

sys.argv	List of command line arguments (argv[0] is executable)
os.environ	Dictionary of environment variables
os.curdir	String with path of current directory

import sys; print(sys.argv) or
from sys import argv; print(argv)

String Formatting

"Hello, {0} {1}".format("abe", "jones")
Hello, abe jones

"Hello, {fn} {ln}".format(fn="abe", ln="jones")
Hello, abe jones

"You owe me ${0:,.2f}".format(253422.3)
You owe me $253,422.30

now = datetime.now()
'{:%Y-%m-%d %H:%M:%S}'.format(now)
2012-05-16 15:04:33

Useful Functions

exit( code )	Terminate program with exit code
raw_input("prompt")	Print prompt and readline() from stdin¹

¹ Use input("prompt") in Python 3

Code Snippets

Loop Over Sequence
for index, value in enumerate(seq):
print("{} : {}".format(index, value))

Loop Over Dictionary
for key in sorted(dict):
print(dict[key])

Read a File
with open("filename", "r") as f:
for line in f:
line = line.rstrip("\n") # Strip newline
print(line)

Other References

http://rgruet.free.fr/
Great Python 2.x Quick Reference

http://www.cheatography.com/davechild/cheat-sheets/python/
More Python Cheatsheet Goodness

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Comments (1)

olorinj 07:51 22 Mar 2016

Amazing cheatsheet.