Syntax

if / elif / else

if condition:
    ...
elif condition:
    ...
else:
    ...

for loop

for item in iterable:
    ...

while loop

while condition:
    ...

function

def name(param):
    return value

class

class Name:
    def __init__(self):
        ...

try / except

try:
    ...
except ErrorType:
    ...

list comprehension

[x for x in lst
 if condition]

lambda

f = lambda x: x * 2

import

import module
from module import name

Common Errors

SyntaxError

Code isn't valid Python. Check for missing colons, brackets, or quotes.

IndentationError

Inconsistent spaces/tabs. Use 4 spaces per indent level consistently.

NameError

Variable used before being defined. Check spelling and order of code.

TypeError

Wrong type for an operation, e.g. adding a string to an int.

IndexError

Accessing a list index that doesn't exist. Lists start at index 0.

KeyError

Dictionary key doesn't exist. Use .get() for safe access.

ZeroDivisionError

Dividing by zero. Add a check before dividing.

AttributeError

Object doesn't have that method or property. Check the type.

ValueError

Right type but wrong value, e.g. int("abc") or math.sqrt(-1).

Built-ins

print()Output to console

input()Read user input

len()Length of list/string

range()Generate number sequence

type()Get type of a value

int()Convert to integer

float()Convert to decimal

str()Convert to string

list()Convert to list

dict()Create dictionary

sorted()Return sorted list

enumerate()Index + value pairs

zip()Pair up two lists

map()Apply func to each item

filter()Keep items matching func

sum()Total of a list

min()/max()Smallest / largest

abs()Absolute value

round()Round a number

open()Open a file

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Variables

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