Built-in Functions

Complete reference for Python’s built-in functions available without importing

Python provides 71 built-in functions that are always available without importing any module. These functions cover common operations like type conversion, iteration, I/O, and more.

Most Commonly Used

These functions are used in almost every Python program:

print()

Output text to the console.

*objects · any

Values to print (converted to strings)

sep · str · default: "' '"

String inserted between values

end · str · default: "'\\n'"

String appended after the last value

file · file · default: "sys.stdout"

File object to write to

print("Hello", "World")  # Hello World
print("A", "B", "C", sep="-")  # A-B-C
print("Loading", end="...\n")  # Loading...

len()

Return the length of an object.

obj · object · required

Any object with a length (string, list, dict, etc.)

return · int

Number of items in the object

len("hello")  # 5
len([1, 2, 3, 4])  # 4
len({'a': 1, 'b': 2})  # 2

type()

Return the type of an object.

object · any · required

Object to get the type of

return · type

The type of the object

type(42)  # <class 'int'>
type("hello")  # <class 'str'>
type([1, 2, 3])  # <class 'list'>

range()

Generate a sequence of numbers.

stop · int · required

End of range (exclusive)

start · int · default: "0"

Start of range (inclusive)

step · int · default: "1"

Increment between values

list(range(5))  # [0, 1, 2, 3, 4]
list(range(2, 10))  # [2, 3, 4, 5, 6, 7, 8, 9]
list(range(0, 10, 2))  # [0, 2, 4, 6, 8]

input()

Read a string from standard input.

prompt · str · default: "''"

Prompt to display before reading input

return · str

String entered by the user

name = input("Enter your name: ")
age = int(input("Enter your age: "))

Type Conversion

Convert between different data types:

int(), float(), str(), bool()

# String to integer
int("42")  # 42
int("FF", 16)  # 255 (hexadecimal)

# String to float
float("3.14")  # 3.14

# Number to string
str(42)  # "42"
str(3.14)  # "3.14"

# To boolean
bool(0)  # False
bool(1)  # True
bool("")  # False
bool("text")  # True

list(), tuple(), set(), dict()

# Convert to list
list("abc")  # ['a', 'b', 'c']
list(range(3))  # [0, 1, 2]

# Convert to tuple
tuple([1, 2, 3])  # (1, 2, 3)

# Convert to set (removes duplicates)
set([1, 2, 2, 3, 3])  # {1, 2, 3}

# Create dictionary from pairs
dict([('a', 1), ('b', 2)])  # {'a': 1, 'b': 2}

Iteration & Sequences

enumerate()

Add counter to an iterable.

fruits = ['apple', 'banana', 'cherry']
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")
# 0: apple
# 1: banana
# 2: cherry

# Start from different index
for i, fruit in enumerate(fruits, start=1):
    print(f"{i}. {fruit}")

zip()

Combine multiple iterables.

names = ['Alice', 'Bob', 'Charlie']
ages = [25, 30, 35]
for name, age in zip(names, ages):
    print(f"{name} is {age} years old")

# Create dictionary from two lists
data = dict(zip(names, ages))
# {'Alice': 25, 'Bob': 30, 'Charlie': 35}

map()

Apply function to every item.

# Square all numbers
numbers = [1, 2, 3, 4, 5]
squared = list(map(lambda x: x**2, numbers))
# [1, 4, 9, 16, 25]

# Convert strings to integers
strings = ['1', '2', '3']
integers = list(map(int, strings))
# [1, 2, 3]

filter()

Filter items based on condition.

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

# Get even numbers
even = list(filter(lambda x: x % 2 == 0, numbers))
# [2, 4, 6, 8, 10]

# Get numbers greater than 5
large = list(filter(lambda x: x > 5, numbers))
# [6, 7, 8, 9, 10]

sorted()

Return sorted list.

# Sort numbers
sorted([3, 1, 4, 1, 5, 9])  # [1, 1, 3, 4, 5, 9]

# Sort in reverse
sorted([3, 1, 4], reverse=True)  # [4, 3, 1]

# Sort by key function
words = ['banana', 'pie', 'Washington', 'book']
sorted(words, key=len)  # ['pie', 'book', 'banana', 'Washington']
sorted(words, key=str.lower)  # ['banana', 'book', 'pie', 'Washington']

reversed()

Reverse an iterable.

list(reversed([1, 2, 3, 4, 5]))  # [5, 4, 3, 2, 1]
list(reversed("hello"))  # ['o', 'l', 'l', 'e', 'h']

Mathematical Functions

sum(), min(), max()

numbers = [1, 2, 3, 4, 5]

sum(numbers)  # 15
min(numbers)  # 1
max(numbers)  # 5

# With start value
sum(numbers, 10)  # 25 (10 + 15)

# Min/max with key
words = ['banana', 'pie', 'Washington']
min(words, key=len)  # 'pie'
max(words, key=len)  # 'Washington'

abs(), round(), pow()

abs(-5)  # 5
abs(-3.14)  # 3.14

round(3.14159, 2)  # 3.14
round(42.5)  # 42

pow(2, 3)  # 8 (2^3)
pow(2, 3, 5)  # 3 (2^3 % 5)

divmod()

Get quotient and remainder.

divmod(17, 5)  # (3, 2)
quotient, remainder = divmod(17, 5)

Object Inspection

isinstance()

Check if object is instance of class.

isinstance(42, int)  # True
isinstance("hello", str)  # True
isinstance([1, 2], (list, tuple))  # True (checks multiple types)

hasattr(), getattr(), setattr()

Work with object attributes.

class Person:
    def __init__(self, name):
        self.name = name

person = Person("Alice")

hasattr(person, 'name')  # True
hasattr(person, 'age')  # False

getattr(person, 'name')  # 'Alice'
getattr(person, 'age', 0)  # 0 (default value)

setattr(person, 'age', 25)
person.age  # 25

dir()

List attributes of an object.

dir([])  # List all list methods
dir(str)  # List all string methods

vars()

Return __dict__ attribute of an object.

class Point:
    def __init__(self, x, y):
        self.x = x
        self.y = y

p = Point(1, 2)
vars(p)  # {'x': 1, 'y': 2}

File Operations

open()

Open a file for reading or writing.

file · str · required

Path to the file

mode · str · default: "'r'"

Opening mode: ‘r’ (read), ‘w’ (write), ‘a’ (append), ‘b’ (binary)

encoding · str · default: "None"

Text encoding (e.g., ‘utf-8’)

# Read file
with open('data.txt', 'r') as f:
    content = f.read()

# Write file
with open('output.txt', 'w') as f:
    f.write('Hello, World!')

# Read lines
with open('data.txt', 'r') as f:
    for line in f:
        print(line.strip())

Advanced Functions

all(), any()

Test if all or any elements are true.

# All elements must be True
all([True, True, True])  # True
all([True, False, True])  # False
all([1, 2, 3])  # True (non-zero numbers are truthy)

# At least one element must be True
any([False, False, True])  # True
any([False, False, False])  # False
any([0, 0, 1])  # True

# Practical examples
numbers = [2, 4, 6, 8]
all(n % 2 == 0 for n in numbers)  # True (all even)

scores = [45, 67, 89, 92]
any(score > 90 for score in scores)  # True (at least one > 90)

eval(), exec()

These functions execute arbitrary Python code and should be used with extreme caution, especially with user input.

# Evaluate expression
result = eval('2 + 3 * 4')  # 14

# Execute code
exec('print("Hello from exec")')

# With variables
x = 5
result = eval('x * 2 + 10')  # 20

compile()

Compile source code into code object.

code = compile('print("Hello")', '<string>', 'exec')
exec(code)  # Hello

globals(), locals()

Access global and local namespaces.

# Global variables
globals()['x'] = 42
print(x)  # 42

# Local variables in function
def func():
    y = 10
    print(locals())  # {'y': 10}

Special Functions

id()

Return unique identifier for an object.

a = [1, 2, 3]
id(a)  # Memory address

b = a
id(b) == id(a)  # True (same object)

hash()

Return hash value of an object.

hash("hello")  # Some integer
hash(42)  # 42
hash((1, 2, 3))  # Tuples are hashable

# Lists are not hashable
# hash([1, 2, 3])  # TypeError

callable()

Check if object is callable.

callable(print)  # True
callable(len)  # True
callable(42)  # False
callable(lambda x: x)  # True

Complete List

Here are all 71 built-in functions:

Complete Alphabetical List

• abs() - Absolute value
• aiter() - Async iterator
• all() - Test if all elements are true
• anext() - Async next
• any() - Test if any element is true
• ascii() - ASCII representation
• bin() - Convert to binary
• bool() - Convert to boolean
• breakpoint() - Debugger breakpoint
• bytearray() - Mutable bytes
• bytes() - Immutable bytes
• callable() - Check if callable
• chr() - Character from code point
• classmethod() - Class method decorator
• compile() - Compile source code
• complex() - Complex number
• delattr() - Delete attribute
• dict() - Dictionary
• dir() - List attributes
• divmod() - Quotient and remainder
• enumerate() - Add counter to iterable
• eval() - Evaluate expression
• exec() - Execute code
• filter() - Filter items
• float() - Convert to float
• format() - Format value
• frozenset() - Immutable set
• getattr() - Get attribute
• globals() - Global namespace
• hasattr() - Check for attribute
• hash() - Hash value
• help() - Interactive help
• hex() - Convert to hexadecimal
• id() - Object identifier
• input() - Read input
• int() - Convert to integer
• isinstance() - Check instance
• issubclass() - Check subclass
• iter() - Create iterator
• len() - Length of object
• list() - List
• locals() - Local namespace
• map() - Map function
• max() - Maximum value
• memoryview() - Memory view
• min() - Minimum value
• next() - Next item from iterator
• object() - Base object
• oct() - Convert to octal
• open() - Open file
• ord() - Code point from character
• pow() - Power
• print() - Print output
• property() - Property decorator
• range() - Range of numbers
• repr() - String representation
• reversed() - Reverse iterable
• round() - Round number
• set() - Set
• setattr() - Set attribute
• slice() - Slice object
• sorted() - Sort iterable
• staticmethod() - Static method decorator
• str() - String
• sum() - Sum of items
• super() - Call parent class
• tuple() - Tuple
• type() - Type of object
• vars() - Object dictionary
• zip() - Combine iterables
• __import__() - Import module

Best Practices

Use built-in functions instead of loops when possible - They’re optimized in C and much faster.

# Slow
total = 0
for num in numbers:
    total += num

# Fast
total = sum(numbers)

Avoid eval() and exec() with untrusted input - they can execute arbitrary code.

Related

Built-in Types

Fundamental data types

itertools

Advanced iteration tools

functools

Higher-order function tools