Common Python Built‑in Functions: 68 Examples with Code

Python is a popular programming language with a powerful standard library. This article presents 68 frequently used built‑in functions, covering numeric, string, list, dictionary, tuple, set, and file operations, each accompanied by concise code examples.

Numeric Functions

### abs()
# Returns the absolute value of a number.
a = -5
print(abs(a))  # 5

### divmod()
# Returns the quotient and remainder of two numbers.
a, b = 10, 3
print(divmod(a, b))  # (3, 1)

### pow()
# Calculates the power of a number.
a, b = 2, 3
print(pow(a, b))  # 8

### round()
# Rounds a number to the nearest integer.
a = 2.8
print(round(a))  # 3

String Functions

### chr()
# Converts an ASCII code to its character.
print(chr(97))  # 'a'

### ord()
# Returns the ASCII code of a character.
print(ord('a'))  # 97

### len()
# Returns the length of a string.
s = 'hello world'
print(len(s))  # 11

### str()
# Converts a value to a string.
a = 123
print(str(a))  # '123'

### capitalize()
# Capitalizes the first character.
s = 'hello world'
print(s.capitalize())  # 'Hello world'

### lower()
# Converts all characters to lowercase.
s = 'Hello World'
print(s.lower())  # 'hello world'

### upper()
# Converts all characters to uppercase.
s = 'Hello World'
print(s.upper())  # 'HELLO WORLD'

### swapcase()
# Swaps case of each character.
s = 'Hello World'
print(s.swapcase())  # 'hELLO wORLD'

### title()
# Capitalizes the first letter of each word.
s = 'hello world'
print(s.title())  # 'Hello World'

### strip()
# Removes leading/trailing spaces or specified characters.
s = '   hello world  '
print(s.strip())  # 'hello world'

### replace()
# Replaces specified characters.
s = 'hello world'
print(s.replace('l', 'i'))  # 'heiioworid'

### split()
# Splits a string by a delimiter.
s = 'hello,world'
print(s.split(','))  # ['hello', 'world']

### join()
# Joins an iterable of strings with a separator.
lst = ['hello', 'world']
print('-'.join(lst))  # 'hello-world'

List Functions

### len()
# Returns the length of a list.
lst = [1, 2, 3, 4, 5]
print(len(lst))  # 5

### max()
# Returns the maximum value in a list.
lst = [1, 2, 3, 4, 5]
print(max(lst))  # 5

### min()
# Returns the minimum value in a list.
lst = [1, 2, 3, 4, 5]
print(min(lst))  # 1

### sum()
# Returns the sum of all elements.
lst = [1, 2, 3, 4, 5]
print(sum(lst))  # 15

### sorted()
# Returns a sorted list.
lst = [3, 1, 4, 2, 5]
print(sorted(lst))  # [1, 2, 3, 4, 5]

### reversed()
# Returns an iterator that yields the list in reverse order.
lst = [1, 2, 3, 4, 5]
print(list(reversed(lst)))  # [5, 4, 3, 2, 1]

### list()
# Converts another iterable to a list.
t = (1, 2, 3)
print(list(t))  # [1, 2, 3]

### append()
# Appends an element to the end of the list.
lst = [1, 2, 3]
lst.append(4)
print(lst)  # [1, 2, 3, 4]

### insert()
# Inserts an element at a specified position.
lst = [1, 2, 3]
lst.insert(1, 4)
print(lst)  # [1, 4, 2, 3]

### remove()
# Removes the first occurrence of a value.
lst = [1, 2, 3]
lst.remove(2)
print(lst)  # [1, 3]

### pop()
# Removes and returns the last element.
lst = [1, 2, 3]
print(lst.pop())  # 3
print(lst)  # [1, 2]

### extend()
# Extends a list by appending elements from another iterable.
lst1 = [1, 2, 3]
lst2 = [4, 5, 6]
lst1.extend(lst2)
print(lst1)  # [1, 2, 3, 4, 5, 6]

### index()
# Returns the first index of a value.
lst = [1, 2, 3, 4, 5]
print(lst.index(3))  # 2

### count()
# Returns the number of occurrences of a value.
lst = [1, 2, 2, 3, 3, 3]
print(lst.count(2))  # 2

Dictionary Functions

### len()
# Returns the number of key‑value pairs.
d = {'a': 1, 'b': 2, 'c': 3}
print(len(d))  # 3

### keys()
# Returns all keys.
print(d.keys())  # dict_keys(['a', 'b', 'c'])

### values()
# Returns all values.
print(d.values())  # dict_values([1, 2, 3])

### items()
# Returns all key‑value pairs.
print(d.items())  # dict_items([('a', 1), ('b', 2), ('c', 3)])

### get()
# Returns the value for a key, or a default.
print(d.get('a'))  # 1
print(d.get('d', 0))  # 0

### pop()
# Removes a key and returns its value.
print(d.pop('b'))  # 2
print(d)  # {'a': 1, 'c': 3}

### update()
# Updates a dictionary with another's key‑value pairs.
d1 = {'a': 1, 'b': 2}
d2 = {'b': 3, 'c': 4}
d1.update(d2)
print(d1)  # {'a': 1, 'b': 3, 'c': 4}

Tuple Functions

### len()
# Returns the number of elements.
t = (1, 2, 3)
print(len(t))  # 3

### max()
# Returns the maximum element.
print(max(t))  # 3

### min()
# Returns the minimum element.
print(min(t))  # 1

### tuple()
# Converts an iterable to a tuple.
lst = [1, 2, 3]
print(tuple(lst))  # (1, 2, 3)

Set Functions

### len()
# Returns the number of elements.
s = {1, 2, 3}
print(len(s))  # 3

### max()
# Returns the maximum element.
print(max(s))  # 3

### min()
# Returns the minimum element.
print(min(s))  # 1

### set()
# Converts an iterable to a set.
lst = [1, 2, 3]
print(set(lst))  # {1, 2, 3}

### add()
# Adds an element to the set.
s.add(4)
print(s)  # {1, 2, 3, 4}

### remove()
# Removes an element from the set.
s.remove(2)
print(s)  # {1, 3}

File Operation Functions

### open()
# Opens a file and returns a file object.
f = open('test.txt', 'r')

### close()
# Closes an opened file.
f.close()

### read()
# Reads the entire file content.
f = open('test.txt', 'r')
print(f.read())
f.close()

### write()
# Writes a string to a file.
f = open('test.txt', 'w')
f.write('hello world
')
f.close()

Other Useful Functions

### isinstance()
# Checks if an object is an instance of a class.
x = 10
print(isinstance(x, int))  # True

### range()
# Generates a sequence of integers.
print(list(range(5)))  # [0, 1, 2, 3, 4]

### zip()
# Aggregates elements from multiple iterables.
lst1 = [1, 2, 3]
lst2 = ['a', 'b', 'c']
print(list(zip(lst1, lst2)))  # [(1, 'a'), (2, 'b'), (3, 'c')]

### map()
# Applies a function to each item of an iterable.
lst = [1, 2, 3]
print(list(map(lambda x: x * 2, lst)))  # [2, 4, 6]

### filter()
# Filters items based on a predicate.
lst = [1, 2, 3, 4, 5]
print(list(filter(lambda x: x % 2 == 0, lst)))  # [2, 4]

### reduce()
# Reduces an iterable to a single value.
from functools import reduce
lst = [1, 2, 3]
print(reduce(lambda x, y: x * y, lst))  # 6

### round()
# Rounds a number.
a = 2.8
print(round(a))  # 3

### open()
# Opens a file (repeated for emphasis).
f = open('test.txt', 'r')
print(f.read())
f.close()

In summary, these 68 built‑in functions provide convenient tools for handling common data types and file operations in Python, helping developers write clearer and more efficient code.