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] = 'this'
d[0:1] = ['this', 'is']
d[0:-1] = ['this', 'is', 'a']
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

arithmetic operators
+        addition
-        subtraction
*        multiplication
/        division
//       floor division
%        modulus
**       exponentiation

&
|

<
<=
>
>=
!=
==
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           # for debugging, will raise AssertionError if 'assert [false]'
break            # break out of for or while loop
continue         # end current iteration in a for or while loop
nonlocal
pass             # placeholder for future code
raise            # raise exception
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[0]                 -> first command line argument 

Files

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

strftime & strptime format

%a    Weekday as locale’s abbreviated name.      Sun, Mon, …, Sat (en_US);So, Mo, …, Sa (de_DE)
%A    Weekday as locale’s full name.             Sunday, Monday, …, Saturday (en_US);Sonntag, Montag, …, Samstag (de_DE)
%w    Weekday as a decimal number. Sundy=0       0, 1, …, 6
%d    Day of the month, zero-padded              01, 02, …, 31
%b    Month as locale’s abbreviated name.        Jan, Feb, …, Dec (en_US);Jan, Feb, …, Dez (de_DE)
%B    Month as locale’s full name.               January, February, …, December (en_US);Januar, Februar, …, Dezember (de_DE)
%m    Month as a zero-padded decimal number.     01, 02, …, 12
%y    Year without century, zero-padded          00, 01, …, 99
%Y    Year with century as a decimal number.     0001, 0002, …, 2013, 2014, …, 9998, 9999
%H    Hour (24-hour clock), zero-padded          00, 01, …, 23
%I    Hour (12-hour clock), zero-padded          01, 02, …, 12
%p    Locale’s equivalent of either AM or PM.    AM, PM (en_US);am, pm (de_DE)
%M    Minute, zero-padded                        00, 01, …, 59
%S    Second,zero-padded                         00, 01, …, 59
%f    Microsecond, zero-padded                   000000, 000001, …, 999999
%z    UTC offset in the form ±HHMM[SS[.ffffff]]  (empty), +0000, -0400, +1030, +063415, -030712.345216
%Z    Time zone name (empty if none)             (empty), UTC, EST, CST
%j    Day of the year, zero-padded               001, 002, …, 366
%U    Week number, Sunday first day of week      00, 01, …, 53
%W    Week number, Monday first day of week      00, 01, …, 53
%c    Locale’s appropriate date and time         Tue Aug 16 21:30:00 1988 (en_US);Di 16 Aug 21:30:00 1988 (de_DE)
%x    Locale’s appropriate date                  08/16/88 (None); 08/16/1988 (en_US); 16.08.1988 (de_DE)
%X    Locale’s appropriate time                  21:30:00 (en_US); 21:30:00 (de_DE)
%%    A literal '%' character.                   %

import os

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

other

iter

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