How to detect lowercase letters in Python?

Question

I need to know if there is a function that detects the lowercase letters in a string. Say I started writing this program:

s = input('Type a word') 

Would there be a function that lets me detect a lowercase letter within the string s? Possibly ending up with assigning those letters to a different variable, or just printing the lowercase letters or number of lowercase letters.

While those would be what I would like to do with it I'm most interested in how to detect the presence of lowercase letters. The simplest methods would be welcome.

Answer 1

To check if a character is lower case, use the islower method of str. This simple imperative program prints all the lowercase letters in your string:

for c in s:     if c.islower():          print c 

Note that in Python 3 you should use print(c) instead of print c.

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Possibly ending up with assigning those letters to a different variable.

To do this I would suggest using a list comprehension, though you may not have covered this yet in your course:

>>> s = 'abCd' >>> lowercase_letters = [c for c in s if c.islower()] >>> print lowercase_letters ['a', 'b', 'd'] 

Or to get a string you can use ''.join with a generator:

>>> lowercase_letters = ''.join(c for c in s if c.islower()) >>> print lowercase_letters 'abd' 

Answer 2

There are 2 different ways you can look for lowercase characters:

1. Use str.islower() to find lowercase characters. Combined with a list comprehension, you can gather all lowercase letters:

   lowercase = [c for c in s if c.islower()] 

2. You could use a regular expression:

   import re  lc = re.compile('[a-z]+') lowercase = lc.findall(s) 

The first method returns a list of individual characters, the second returns a list of character groups:

>>> import re >>> lc = re.compile('[a-z]+') >>> lc.findall('AbcDeif') ['bc', 'eif']