Basics

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

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

Useful functions

Write to the screen print("hi") Calculate length len("test") Minimum of numbers min(1, 2) Maximum of numbers max(1, 2) Cast to integer int("123") Cast to string str(123) Cast to boolean bool(1) Range of numbers range(5, 10)

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

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

if x == 1: print("x is one") else: print("x is not one")

Lists

numbers = [7, 8, 9] first_number = numbers[0] numbers[2] = 11 if 11 in numbers: print("11 is in the list!") for n in numbers: print(n)

Defining functions

def my_func (param1, param2): result = param1 + param2 return result

Loops

for number in [1, 2, 3]: print(number) x = 0 while x < 10: print(x) x = x + 1

Dictionaries

numbers = { 1: "one", 2: "two" } print(numbers[1])

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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