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

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:

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

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

True
False

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:

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

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

True
False

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:

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

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

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:

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

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

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.

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)

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()