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Python String isupper() method - GeeksforGeeks

Last Updated : 11 Jul, 2025

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())  

• 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.

string.isupper()

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

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

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())  

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

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

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

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

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

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

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

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())  

• 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.

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

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

• 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.

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