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 % modulus ** exponentiation // floor division ##### comparison operators ##### == equal != not equal < less than <= less than or equal to > greater than >= greater than or equal to is is not in not in and or not ##### bitwise operators ##### & and | or ^ xor ~ not << >>
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 = '''multiline
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)
Lambda
small function, with any number of arguments
x = lambda a : a + 10 print(x(5)) x = lambda a, b : a * b print(x(5, 6))
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()