Uppercase and Lowercase Strings in Python (Conversion and Checking)

In Python, the string type (str) has methods for handling uppercase and lowercase characters. You can convert characters to different cases and check their case.

• Built-in Types - String Methods — Python 3.11.4 documentation

If you want to check if a string contains digits or letters, see the following article:

• Check if a string is numeric, alphabetic, alphanumeric, or ASCII

Convert between uppercase and lowercase

Basic usage

First, let's review the basic usage. This example uses the upper() method to convert all characters to uppercase, but the other methods work similarly.

In Python, string objects (str) are immutable; thus, the original string remains unmodified.

s_org = 'pYThon proGramminG laNguAge'

print(s_org.upper())
# PYTHON PROGRAMMING LANGUAGE

print(s_org)
# pYThon proGramminG laNguAge

If you want to use the converted string later, you can assign it to a new variable like this:

s_new = s_org.upper()
print(s_new)
# PYTHON PROGRAMMING LANGUAGE

You can also overwrite the original variable.

s_org = s_org.upper()
print(s_org)
# PYTHON PROGRAMMING LANGUAGE

Convert to uppercase: str.upper()

s_org = 'pYThon proGramminG laNguAge'

print(s_org.upper())
# PYTHON PROGRAMMING LANGUAGE

Convert to lowercase: str.lower()

s_org = 'pYThon proGramminG laNguAge'

print(s_org.lower())
# python programming language

Capitalize string: str.capitalize()

The capitalize() method converts the first character of the string to uppercase and the rest to lowercase.

s_org = 'pYThon proGramminG laNguAge'

print(s_org.capitalize())
# Python programming language

Convert to title case: str.title()

The title() method converts the first character of each word in the string to uppercase and the rest to lowercase.

s_org = 'pYThon proGramminG laNguAge'

print(s_org.title())
# Python Programming Language

Swap uppercase and lowercase letters: str.swapcase()

s_org = 'pYThon proGramminG laNguAge'

print(s_org.swapcase())
# PytHON PROgRAMMINg LAnGUaGE

Check uppercase and lowercase characters

In the following examples, methods are called directly on string literals, such as 'python', but they can also be used with strings stored in variables.

print('PYTHON'.isupper())
# True

print('Python'.isupper())
# False

Characters without case distinction

Characters without case distinctions, such as numbers and symbols, are ignored. If the string contains only these characters, the following methods return False.

print('[123]'.isupper())
# False

Check if all characters are uppercase: str.isupper()

The isupper() method returns True if the string contains at least one alphabetic character, all of which are uppercase; otherwise, it returns False.

print('PYTHON'.isupper())
# True

print('Python'.isupper())
# False

Check if all characters are lowercase: str.islower()

The islower() method returns True if the string contains at least one alphabetic character, all of which are lowercase; otherwise, it returns False.

print('python'.islower())
# True

print('Python'.islower())
# False

Check if the string is title case: str.istitle()

The istitle() method returns True if the string is title case (i.e., the first character of each word is uppercase, and the rest are lowercase); otherwise, it returns False.

print('Python Programming Language'.istitle())
# True

print('PYTHON Programming Language'.istitle())
# False

Note that the istitle() method returns False if a word starts with characters without case distinctions followed by lowercase letters.

print('The 1st Team'.istitle())
# False

print('The 1St Team'.istitle())
# True