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Learn python coding and syntax by carefully going through this cheat sheet
Typology: Cheat Sheet
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Python is white-space dependent; code blocks are indented 4 spaces (not tabs) Variable Assignment integer = 1 string = “string” unicode_string = u”unicode string” mutli_line_string = “““ multi-line string ””” tuple = ( element1, element2, element3, … ) list = [ element1, element2, element3, ... ] dictionary = { key1 : value1 , key2 : value2, ... } dictionary[key] = value class_instance = ClassName(init_args)
Frequently Used Built-in Types True False None str unicode int float list dict Other than True , False and None , these can also be used as functions to explicitly cast a value to that type
Functions def function_name(arg1, arg2, keyword1=val1, keyword2=val2, ...) :
my_function(1, 2) → 3 my_function(1, 2, 3) → 6 my_function(1, 2, y=4) → 7
Classes class ClassName(SuperClass): class_variable = static_value def init( self , value1, <...>): self. instance_variable1 = value self. instance_function () def instance_function ( self , arg1 , <...> ):
MyClass.offset → 1
c = MyClass(2) c.value → 2 c.get_offset_value() → 3
Imports import module from module import c lass, function, variable
Frequently Used String Manipulations string1 + string1 “str” + “ing” → “string” "%s%s" % ( string1 , string2 ) “%s%s” % (“s”, “g”) → “sg” string .split(" delim ", limit ) “s/g”.split(“/”) → [“s”, “g”] string .strip() “ string “.strip() → “string” string .startswith ("prefix") “str”.startswith(“s”) → True substring in string “str” in “string” → True print string
List Comprehension [ value for value in list if condition ] e.g. [x for x in [1,2,3,4,5,6,7,8,9] if x % 2 == 0] → [2,4,6,8]
Accessing Variable Values value = dictionary [ key ] value = dictionary .get( key , default_value ) value = list [ index ] e.g. [5,6,7][2] → 7 value = string [ start : end ] e.g “string”[0:3] → “str” value = list [ start : end ] e.g. [1,2,3][1:2] → [2] value = ClassName. class_variable value = class_instance. instance_variable value = class_instance. function(args)
Comparisons value1 == value2 “str” == “str” → True value1 != value2 “str” != “str” → False value1 < value2 1 < 2 → True value1 <= value2 2 <= 2 → True value1 > value2 2 > 3 → False value1 >= value2 3 >= 3 → True value is [ not] None value in list 1 in [2,3,4] → False i sinstance ( class_instance , ClassName )
Basic Arithmetic i = a + b i = a - b i = a / b i = a * b i = a % b e.g. 11 % 3 → 2
Comments """ Multi-line comment """
# Line Comment
Control Flow if conditional : elif conditional : else :
e.g.
if i == 7: print “seven” elif i == 8: print “eight” else : print str(i) for value in list : continue break
e.g.
for i in [1, 2, 3, 4]: if i == 2: continue if i == 3: break print i while conditional : continue break
e.g.
while True: print “infinity”
Exceptions try: raise Exception() except Exception as e :
e.g.
try: database.update() except Exception as e : log.error(e.msg) database.abort() finally: database.commit()
File & Path Manipulation import os # import the os module first os.path.join( path_segment1 , path_segment2 , ...) os.path.exists( path ) os.listdir( directory_path ) os.remove (file_path) os.rmdir (directory_path) file = open( path , "rw") file .read() string .write ("string")