Python Cheat Sheet 2020



Python cheat sheet 2020

Basics

Python Cheat Sheet - Complex Data Types “ A puzzle a day to learn, code, and play ” → Visit f inxter.com Description Example List A container data type that stores a sequence of elements. Unlike strings, lists are mutable: modification possible. L = 1, 2, 2 print(len(l)) # 3 Adding elements. Python Cheat Sheet - Classes “ A puzzle a day to learn, code, and play ” → Visit f inxter.com Description Example Classes A class encapsulates data and functionality - data as attributes, and functionality as methods. It is a blueprint to create concrete instances in the memory. Python Cheat Sheet - Keywords “ A puzzle a day to learn, code, and play ” → Visit f inxter.com Keyword Description Code example False, True Data values from the data type Boolean False ( 1 2 ), True ( 2 1 ) and, or, not Logical operators.

Python

Variables Assignment, Math Ops, Precedence, and PrintGet Data Types Boolean List DICTIONARY STRINGS TUPLES SETS Comparison, Logical Operators, Conditional Statements COMPARISON OPERATORS LOGICAL OPERATORS CONDITIONAL STATEMENTS If the condition is Read More.

Print a number print(123)
Print a string print('test')
Adding numbers print(1+2)
Variable assignment number = 123
Print a variable print(number)
Function call x = min(1, 2)
Comment # a comment

Types

Python
Integer 42
String 'a string'
List [1, 2, 3]
Tuple (1, 2, 3)
Boolean True

Useful functions

Cheat
Write to the screen print('hi')
Calculate lengthlen('test')
Minimum of numbersmin(1, 2)
Maximum of numbersmax(1, 2)
Cast to integerint('123')
Cast to stringstr(123)
Cast to booleanbool(1)
Range of numbersrange(5, 10)
Cheat

Other syntax

Return a value return 123
Indexing 'test'[0]
Slicing 'test'[1:3]
Continue to next loop iteration continue
Exit the loop break
List append numbers = numbers + [4]
List append (with method call) numbers.append(4)
List item extraction value = numbers[0]
List item assignment numbers[0] = 123

Terminology

syntax the arrangement of letters and symbols in code
program a series of instructions for the computer
print write text to the screen
string a sequence of letters surrounded by quotes
variable a storage space for values
value examples: a string, an integer, a boolean
assignment using = to put a value into a variable
function a machine you put values into and values come out
call (a function) to run the code of the function
argument the input to a function call
parameter the input to a function definition
return value the value that is sent out of a function
conditional an instruction that's only run if a condition holds
loop a way to repeatedly run instructions
list a type of value that holds other values
tuple like a list, but cannot be changed
indexing extracting one element at a certain position
slicing extracting some elements in a row
dictionary a mapping from keys to values

Reminders

Basic Python Cheat Sheet

  • Strings and lists are indexed starting at 0, not 1
  • Print and return are not the same concept
  • The return keyword is only valid inside functions
  • Strings must be surrounded by quotes
  • You cannot put spaces in variable or function names
  • You cannot add strings and integers without casting
  • Consistent indentation matters
  • Use a colon when writing conditionals, function definitions, and loops
  • Descriptive variable names help you understand your code better

Conditionals

Lists

Defining functions

Loops

Dictionaries

Comparisons

Equals
Not equals !=
Less than <
Less than or equal <=
Greater than >

Useful methods

String to lowercase 'xx'.lower()
String to uppercase 'xx'.upper()
Split string by spaces 'a b c'.split(' ')
Remove whitespace around string ' a string '.strip()
Combine strings into one string ' '.join(['a', 'b'])
String starts with 'xx'.startswith('x')
String ends with 'xx'.endswith('x')
List count [1, 2].count(2)
List remove [1, 2].remove(2)
Dictionary keys {1: 2}.keys()
Dictionary values {1: 2}.values()
Dictionary key/value pairs {1: 2}.items()

Other neat bonus stuff

Zip lists zip([1, 2], ['one', 'two'])
Set my_set = {1, 2, 3}
Set intersection {1, 2} & {2, 3}
Set union {1, 2} | {2, 3}
Index of list element [1, 2, 3].index(2)
Sort a list numbers.sort()
Reverse a list numbers.reverse()
Sum of list sum([1, 2, 3])
Numbering of list elements for i, item in enumerate(items):
Read a file line by line for line in open('file.txt'):
Read file contents contents = open('file.txt').read()
Random number between 1 and 10 import random; x = random.randint(1, 10)
List comprehensions [x+1 for x in numbers]
Check if any condition holds any([True, False])
Check if all conditions hold all([True, False])

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