isupper(), islower(), lower(), upper() in Python and their applications (original) (raw)

Last Updated : 03 May, 2025

Python provides several built-in string methods to work with the case of characters. Among them, **isupper(), **islower(), **upper() and **lower() are commonly used for checking or converting character cases. In this article we will learn and explore these methods:

1. isupper() Method

The **isupper() method checks whether all the characters in a string are uppercase.

**For example:

**Input: string = 'GEEKSFORGEEKS'
**Output: True

Syntax of isupper()

string.isupper()

**Parameters:

• isupper() does not take any parameters

**Return Type:

• **True if all alphabetic characters are uppercase.
• **False otherwise.

**Example:

Python `

s = 'GEEKSFORGEEKS' print(s.isupper())

s = 'GeeksforGeeks' print(s.isupper())

`

2. islower() Method

The islower() method checks whether all the characters in a string are lowercase.

**For example:

**Input: string = 'geeksforgeeks'
**Output: True

Syntax of islower()

string.islower()

**Parameters:

• islower() does not take any parameters

**Return Type:

• **True if all alphabetic characters are lowercase.
• **False otherwise.

**Example:

Python `

s = 'geeksforgeeks' print(s.islower())

s = 'GeeksforGeeks' print(s.islower())

`

3. lower() Method

The lower() method returns a copy of the string with all uppercase characters converted to lowercase.

**For example:

**Input: string = 'GEEKSFORGEEKS'
**Output: geeksforgeeks

Syntax of lower()

**Syntax: string.lower()

**Parameters:

• lower() does not take any parameters

**Returns: A new string in all lowercase.

**Example:

Python `

s = 'GEEKSFORGEEKS' print(s.lower())

s = 'GeeksforGeeks' print(s.lower())

`

Output

geeksforgeeks geeksforgeeks

Note: Digits and symbols remain unchanged

4. upper() Method

The upper() method returns a copy of the string with all lowercase characters converted to uppercase.

**For example:

**Input: string = 'geeksforgeeks'
**Output: GEEKSFORGEEKS

Syntax of upper()

string.upper()

**Parameters:

• upper() does not take any parameters

**Returns: A new string in all uppercase.

**Example:

Python `

s = 'geeksforgeeks' print(s.upper())

s = 'My name is Prajjwal' print(s.upper())

`

Output

GEEKSFORGEEKS MY NAME IS PRAJJWAL

Application: Count Uppercase, Lowercase Letters and Spaces

In this example we will count the number of uppercase, lowercase and space characters and toggle the case of each character of a string.

Python `

s = 'GeeksforGeeks is a computer Science portal for Geeks' ns = '' cu = 0 cl = 0 cs = 0

for ch in s: if ch.isupper(): cu += 1 ns += ch.lower() elif ch.islower(): cl += 1 ns += ch.upper() elif ch.isspace(): cs += 1 ns += ch

print("In original String:") print("Uppercase -", cu) print("Lowercase -", cl) print("Spaces -", cs) print("After changing cases:") print(ns)

`

Output

In original String: Uppercase - 4 Lowercase - 41 Spaces - 7 After changing cases: gEEKSFORgEEKS IS A COMPUTER sCIENCE PORTAL FOR gEEKS

**Related article:

• islower()
• isupper()
• lower()
• upper()