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
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| Integer | 42 |
| String | 'a string' |
| List | [1, 2, 3] |
| Tuple | (1, 2, 3) |
| Boolean | True |
Useful functions
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| 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) |
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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
Lists
Defining functions
Loops
Dictionaries
Comparisons
| Equals |
| Not equals | != |
| Less than | < |
| Less than or equal | <= |
| Greater than | > |
Useful methods
Beginner Python Cheat Sheet
| 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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