Python program to check if lowercase letters exist in a string

Checking for the presence of lowercase letters involves scanning the string and verifying if at least one character is a lowercase letter (from 'a' to 'z').

Python provides simple and efficient ways to solve this problem using built-in string methods and constructs like loops and comprehensions.

Using any() with islower()

This method uses the any() function to check if any character in the string is a lowercase letter.

s = "GeeksForGeeks"
# Check for lowercase letters
res = any(c.islower() for c in s)
print(res)  

True

Explanation:

• The any() function checks if any condition is true for elements in an iterable.
• The islower() method checks if a character is lowercase.
• If any lowercase letter exists, the result will be true.

Let's explore some more methods and see how we can check if lowercase letters exist in a string.

Using for loop

This method iterates through each character in the string and checks for lowercase letters.

s = "GeeksForGeeks"
# Initialize result
res = False
# Check for lowercase letters
for c in s:
    if c.islower():
        res = True
        break
print(res)  

True

Explanation:

• A for loop iterates through the string.
• The islower() method checks if a character is lowercase.
• If a lowercase letter is found, the loop breaks and the result is true.

Using list comprehension

This method collects all lowercase letters into a list and checks if the list is non-empty.

s = "GeeksForGeeks"
# Check for lowercase letters
res = len([c for c in s if c.islower()]) > 0
print(res)

True

Explanation:

• A list comprehension collects all lowercase letters in the string.
• The islower() method is used to filter lowercase letters.
• The len() function checks if the list contains any elements.

Using regular expressions

This method uses the re module to search for any lowercase letter in the string.

import re
# Input string
s = "GeeksForGeeks"
# Check for lowercase letters
res = bool(re.search(r"[a-z]", s))
print(res) 

True

Explanation:

• The re.search() function looks for a pattern in the string.
• The pattern [a-z] matches any lowercase letter.
• If a match is found, the result is true.

Using filter()

This method applies the filter() function to extract lowercase letters from the string.

s = "GeeksForGeeks"
# Check for lowercase letters
res = bool(list(filter(str.islower, s)))
print(res)  

True

Explanation:

• The filter() function applies the islower() method to each character.
• A list is created containing all lowercase letters.
• The bool() function checks if the list is non-empty.