Python String and List Built-in Functions Reference

Posted on Mar 30, 2026 in Computer Engineering

Python String Built-in Functions

Case Conversion Functions

upper()

👉 Definition: Converts all characters in a string to uppercase. It returns a new string without modifying the original.

👉 Example: "hello".upper() # "HELLO"

lower()

👉 Definition: Converts all characters in a string to lowercase.

👉 Example: "HELLO".lower() # "hello"

title()

👉 Definition: Capitalizes the first letter of every word and converts the remaining letters to lowercase.

👉 Example: "hello world".title() # "Hello World"

capitalize()

👉 Definition: Capitalizes only the first character of the string and converts the rest to lowercase.

👉 Example: "hello WORLD".capitalize() # "Hello world"

swapcase()

👉 Definition: Converts uppercase letters to lowercase and vice versa.

👉 Example: "AbC".swapcase() # "aBc"

Searching Functions

find(sub)

👉 Definition: Returns the index of the first occurrence of the substring. Returns -1 if not found.

👉 Example: "hello".find("l") # 2

index(sub)

👉 Definition: Returns the index of the substring; raises a ValueError if the substring is not found.

rfind(sub)

👉 Definition: Searches for the substring from the right side and returns the index of the last occurrence.

count(sub)

👉 Definition: Returns the number of times a substring appears in the string.

👉 Example: "hello".count("l") # 2

Boolean Checking Functions

  • isalnum(): Checks if the string contains only alphanumeric characters.
  • isalpha(): Checks if the string contains only alphabets.
  • isdigit(): Checks if the string contains only digits (0–9).
  • islower(): Checks if all letters in the string are lowercase.
  • isupper(): Checks if all letters in the string are uppercase.
  • isspace(): Checks if the string contains only whitespace.
  • startswith(): Checks if the string starts with a specific substring.
  • endswith(): Checks if the string ends with a specific substring.

Replace and Strip Functions

replace(old, new)

👉 Definition: Replaces occurrences of the old substring with the new one.

👉 Example: "hello".replace("l","x") # "hexxo"

strip()

👉 Definition: Removes leading and trailing whitespace.

lstrip() / rstrip()

👉 Definition: Removes whitespace from the left side (lstrip) or right side (rstrip) only.

Split and Join

split()

👉 Definition: Splits a string into a list based on a separator.

👉 Example: "a,b,c".split(",") # ['a','b','c']

join()

👉 Definition: Joins list elements into a string using a specified separator.

👉 Example: ",".join(['a','b']) # "a,b"

Python List Built-in Functions

Adding Elements

append(x)

👉 Definition: Adds a single element to the end of the list.

extend(iterable)

👉 Definition: Adds all elements of an iterable to the end of the list.

insert(i, x)

👉 Definition: Inserts an element at a specific index.

Removing Elements

remove(x)

👉 Definition: Removes the first occurrence of the specified element.

pop([i])

👉 Definition: Removes and returns the element at the given index (or the last element if no index is provided).

clear()

👉 Definition: Removes all elements from the list.

Sorting and Reversing

sort()

👉 Definition: Sorts the list in ascending order in-place.

reverse()

👉 Definition: Reverses the order of elements in the list.

General Utility Functions

  • len(): Returns the total count of elements.
  • max(): Returns the largest element.
  • min(): Returns the smallest element.
  • sum(): Returns the total of all numeric elements.