Python String isupper() method

isupper() method in Python checks if all the alphabetic characters in a string are uppercase. If the string contains at least one alphabetic character and all of them are uppercase, the method returns True. Otherwise, it returns False.

Let's understand this with the help of an example:

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

True

Explanation:

• The string 's' contains only uppercase alphabetic characters.
• Therefore, the isupper() method returns True.
• This method helps us verify that all characters intended to be uppercase are correctly formatted.

Syntax of method

string.isupper()

Parameters

• The isupper() method does not take any parameters.

Return Type

• Returns True if all alphabetic characters in the string are uppercase.
• Returns False if the string contains lowercase letters or non-alphabetic characters.

Examples of method

Checking a string with all uppercase letters

Let’s examine a case where the string is entirely uppercase, we can use this to validate input when uppercase formatting is required, such as for acronyms or constants.

s1 = "PYTHON"
print(s1.isupper())  

True

Explanation:

• The string s1 is made up entirely of uppercase alphabetic characters.
• The method returns True, confirming that all alphabetic characters in s1 are uppercase.

Checking a string with mixed case letters

This method is helpful when we want to ensure that no lowercase letters are present in a string.

s2 = "PyThOn"
print(s2.isupper())  

False

Explanation:

• The string s2 contains both uppercase (P, T, O) and lowercase (y, h, n) characters.
• As a result, isupper() returns False.

Checking a string with non-alphabetic characters

Let’s check how isupper() behaves when the string contains numbers or special characters.

s3 = "123#@!"
print(s3.isupper())  

False

Explanation:

• The string s3 contains only non-alphabetic characters (numbers and special symbols).
• Since there are no uppercase alphabetic characters, isupper() returns False.

String with spaces and uppercase letters

This method is useful when validating input strings with uppercase letters and spaces, such as titles or banners.

s4 = "PYTHON IS FUN"
print(s4.isupper())  

True

Explanation:

• The string s4 contains uppercase alphabetic characters and spaces.
• Spaces are non-alphabetic characters and do not affect the result.
• The method returns True, confirming that all alphabetic characters in s4 are uppercase.

5. An empty string

This is useful when we want to ensure that we’re working with meaningful input before applying further processing.

s5 = ""
print(s5.isupper())  

False

Explanation:

• The string s5 is empty and does not contain any characters.
• The isupper() method returns False since there are no uppercase alphabetic characters to validate.