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Python Language & Syntax Cheat Sheet, Cheat Sheet of Programming Languages
Quick cheat sheet on Python Language & Syntax
Typology: Cheat Sheet
2019/2020
1 / 1
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Download Python Language & Syntax Cheat Sheet and more Cheat Sheet Programming Languages in PDF only on Docsity! Python Language & Syntax Cheat Sheet 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, ...): <function body> return return_value e.g. def my_function(x, y, z=0): sum = x + y + z return sum 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 = value1 self.instance_function() def instance_function(self, arg1, <...>): <function body> return return_value e.g. class MyClass(object): offset = 1 def __init__(self, value): self.value = value def get_offset_value(self): return MyClass.offset + self.value MyClass.offset → 1 c = MyClass(2) c.value → 2 c.get_offset_value() → 3 Imports import module from module import class, 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] by Cottage Labs (http://cottagelabs.com) for Dev8D (http://www.dev8d.org/) 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 isinstance(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: <body> elif conditional: <body> else: <body> e.g. if i == 7: print “seven” elif i == 8: print “eight” else: print str(i) for value in list: <body> continue break e.g. for i in [1, 2, 3, 4]: if i == 2: continue if i == 3: break print i while conditional: <body> continue break e.g. while True: print “infinity” Exceptions try: <body> raise Exception() except Exception as e: <exception handling> finally: <clean-up> 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")
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