Python/CheatSheet

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Python Shebang

#!/usr/bin/env python3

Comments

# This is a comment
print("Hello, World!")

Variables

Tuples

• not changeable

a = (1,2,3)
b = ("test", "with", "strings")

b[0]
-> test

Lists

• changeable

c = [4,5,6]
d = ["this", "is", "a", "list"]

d[0]                             -> 'this'

d[0] = 'new'
d[0:1] = ['new', 'stuff']
d.index(x)                       # Return index of the first item whose value is x
len(d)                           # length
'term' in d                      # find
d.count('new')                   # count number of 'new'

d.append('dude')                 # add item to list
d.extend(['more', 'elements']    # Extend the list by appending all the items from the iterable
d.insert(i,x)                    # Insert an item at a given position

del d[0:1]                       # remove item at given index
d.remove(x)                      # Remove the first item from the list whose value is x
d.pop()                          # Remove the item at the given position in the list
d.clear()                        # remove all items

d.reverse()                      # reverse elements in place
d.sort(key=None, reverse=False)  # sort the items of the list

• list comprehension

[expression for item in list (if condition)]

[x*5 for x in range(5)]                -> [0, 5, 10, 15, 20]
[x for x in range(5) if x%2 == 0]      -> [0, 2, 4]
[i*i for i in range(5)]                -> [0, 1, 4, 9, 16]

Dictionaries

• mapping

e = {'size':5, 'color':'red', 'weight':100}

e['size']
-> 5

keys = ['a', 'b', 'c']
values = [1, 2, 3]
dictionary = dict(zip(keys, values))

for k, v in e.items():
    print (k, v)

e[k]
e[k] = x
e.clear()
e.copy()
del e[k]
e.get(k,x)
k in e
k not in e
e.items()
e.keys()
e.popitem()
e.setdefault()
e1.update(e2)
e.values()

import copy new_dict = copy.deepcopy(old_dict)

Assigning values

x = 1
first, second, third = sequence
x, y = 0, 1
x, y = y, x+y
x, _, y = (1, 2, 3) 
y += 1

Operators

+
-
*
/
//
%
**

&
|

<
<=
>
>=
!=
==
is
is not
in
not in
and
or

Flow Control

If Then Else

if x < 0:
    print('Negative')
elif x == 0:
    print('Zero')
else:
    print('More')

For loops

for x in ['cat', 'dog', 'bird']:
    print (x)

for i in [1,2,3,4,5]:
    print (i+10)

for item in container:
    if search_something(item):
        print(item)             # Found it!
        break
else:
       not_found_in_container() # Didn't find anything..

for index, element in enumerate(newarticles):
    print(index, element)

While loops

while test:
    print (answer)

while True:
    print (answer)
    if answer == '2':
        break

x = 0
while x < 50:
    x = x+1    

try ... except

try:
    result = x / y
except ZeroDivisionError:
     print("division by zero!")
else:
     print("result is", result)
finally:
     print("executing finally clause")

Statements

assert
break
continue
del
exec
global
import
nonlocal
pass
raise
return
yield

Strings

string = "Hello World"
string = 'Hello World'
string 

string[4]                             # = 'o'
string[-1]                            # = 'd'
string[:-7]                           # = 'Hell'
string.split(' ')                     # ['Hello', 'World']

String functions

capitalize()
center(width)
count(sub,start,end)
decode()
encode()
endswith(sub)
expandtabs()
find(sub,start,end)
index(sub,start,end)
isalnum()
isalpha()
isdigit()
islower()
isspace()
istitle()
isupper()
join()
ljust(width)
lower()
lstrip()
partition(sep)
replace(old,new)
rfind(sub,start,end)
rindex(sub,start,end)
rjust(width)
rpartition(sep)
rsplit(sep)
rstrip()
split(sep)
splitlines()
startswith(sub)
strip()
swapcase()
title()
translate(table)
upper()
zfill(width)

Input & Output

x = input("input:")

print(x+12)
print("Hello world")
print("Integer: %i, Float: %6.2f" % (123, 12.043))
print("Integer: {intvar:i}, Float: {floatvar:.2f}")
print("value of x: {0:05d}".format(x))
print("%3i%6s" % (i, chr(i)))

import sys
sys.argv[1]

Files

file = open (ordersfile, 'rb')
file.read()
file.readline()
file.close()

import pickle

with open(ordersfile, 'wb') as fp:
    pickle.dump(orders, fp)

with open (ordersfile, 'rb') as fp:
    orders = pickle.load(fp)

import os.path
os.path.exists(file_path)

Escape sequences

ES	Note
\\	backslash
\'	'
\"	"
\b	backspace
\f	form feed
\n	line feed
\t	horizontal tab
\v	vertical tab
\N{Name}	Unicode by name
\uxxxx	16bit unicode
\uxxxxxxxx	32bit unicode
\123	ASCII code
\xhh	Extended ASCII code (hex)

Double underscore variables

• __file__
  • path of script

import os
os.path.split(__file__)[0] + '/'

• __name__
  • name of submodule or "__main__", if script is directly started

Functions

user defined functions

def userfunction():
    print("Hello")

userfunction()

def userfunction(variable):
    print("Hello", variable)

userfunction('Peter')

def userfunction(variable):
    print("Hello", variable)
    test = 2
    return test
 
print(userfunction('Peter'))    # prints "2"

def userfunction(variable1, variable2 = "John"):
    print("Hello", variable1, variable2)

userfunction("dear")

def userfunction(*variables):
    for var in variables:
        print(var)

userfunction(1,2,3,4)

import datetime

today()
now(timezoneinfo)
utcnow()
fromordinal(ordinal)
combine(date,time)
strptime(date,format)
fromtimestamp(timestamp)
utcfromtimestamp(timestamp)

import time

replace()
utcoffset()
isoformat()
__str__()
dst()
tzname()
strftime(format)
sleep()

timeit

from timeit import default_timer as timer

start = timer()
do_something()
end = timer()

print(end-start)

import os

with ignored(OSError):
    os.remove('somefile.tmp')

other

iter

range
xrange
sorted()
sorted,x, reverse=True)
reversed()