Python: Capitalize the first letter of each word in a string?

In this article we will discuss 5 different ways to convert first letter of each word in a string to uppercase. We will also discuss what are the limitations of each approach and which one is best for us.

Use title() to capitalize the first letter of each word in a string in python

Python Str class provides a member function title() which makes each word title cased in string. It means, it converts the first character of each word to upper case and all remaining characters of word to lower case.

Let’s use this to capitalize the first letter of each word in a string,

sample_text = "this is a sample string"

# Capitalize the first letter of each word i.e.
# Convert the first letter of each word to Upper case and all other to lower case
result = sample_text.title()

print(result)

Output:

This Is A Sample String

It worked fine with this solution, but there is a caveat. The title() function not only capitalize the first letter of each word in a string but also makes all remaining characters of each word to upper case. For example,

sample_text = "33a. it's GONE too far"

# Capitalize the first letter of each word
result = sample_text.title()

print(result)

Output:

33A. It'S Gone Too Far

There are 3 unexpected behaviors in above example,

• In this example it converted “GONE” to “Gone”, because for each word in string it makes only first character as upper case and all remaining characters as lower case.
• It converted “it’s” to “It’S” , because it considered “it’s” as two separate words.
• It converted “33a” to “33A” , because it considered “a” as the first letter of word ’33a’.

So, title() function is not the best solution for capitalizing the first letter of each word in a string. Let’s discuss an another solution,

Use capitalize() to capitalize the first letter of each word in a string

Python’s Str class provides a function capitalize(), it converts the first character of string to upper case. Where as it is already in upper case then it does nothing.

We can use this capitalize() to capitalize the first letter of each word in a string. For that, we need to split our string to a list of words and then on each word in the list we need to call the capitalize() function. Then we need to join all the capitalized words to form a big string.

Let’s understand this with an example,

def capitalize_each_word(original_str):
    result = ""
    # Split the string and get all words in a list
    list_of_words = original_str.split()
    # Iterate over all elements in list
    for elem in list_of_words:
        # capitalize first letter of each word and add to a string
        if len(result) > 0:
            result = result + " " + elem.strip().capitalize()
        else:
            result = elem.capitalize()
    # If result is still empty then return original string else returned capitalized.
    if not result:
        return original_str
    else:
        return result

sample_text = "33a. it's GONE too far"

result = capitalize_each_word(sample_text)

print(result)

Output:

33a. It's Gone Too Far

It converted the first letter of each word in string to upper case.

Instead of writing the big function, we can achieve same using generator expressions i.e.

sample_text = "33a. it's GONE too far"

result = ' '.join(elem.capitalize() for elem in sample_text.split())

print(result)

Output:

33a. It's Gone Too Far

Here we split the string to words and iterated our each word in string using generator expression. While iterating, we called the capitalized() function on each word, to convert the first letter to uppercase and the joined that word to a string using ‘ ‘ as delimiter.

It served the purpose, but there can be one issue in this approach i.e. if words in original string are separated by more than one white spaces or tabs etc. Then this approach can cause error, because we are joining all capitalized words using same delimiter i.e. a single white space. Checkout this example,

sample_text = "this     is       a      sample   string"

result = ' '.join(elem.capitalize() for elem in sample_text.split())

print(result)

Output:

This Is A Sample String

Here original string had multiple spaces between words, but in our final string all capitalized words are separated by a single white space. For some this might not be the correct behavior. So, to rectify this problem checkout our next approach.

Using string.capwords() to capitalize the first letter of each word in a string

Python’s string module provides a function capwords() to convert the first letter to uppercase and all other remaining letters to lower case.
It basically splits the string to words and after capitalizing each word, joins them back using a given seperator. Checkout this example,

import string

sample_text = "it's gone tOO far"

result = string.capwords(sample_text)

print(result)

Output:

It's Gone Too Far

Problem with is solution is that it not only converts the first letter of word to uppercase but also makes the remaining letters of word to lower case. For some, this might not be the correct solution.

So, let’s discuss our final and best solution that does what’s only expected from it.

Using Regex to capitalize the first letter of each word in a string

Using regex, we will look for the starting character of each word and the convert to uppercase. For example,

import re

def convert_to_uupercase(m):
    """Convert the second group to uppercase and join both group 1 & group 2"""
    return m.group(1) + m.group(2).upper()

sample_text = "it's gone   tOO far"

result = re.sub("(^|\s)(\S)", convert_to_uupercase, sample_text)

print(result)

Output:

It's Gone   TOO Far

It capitalized only first character of each word in string and do not modifies the whitespaces between words.

How did it worked ?

We created use a pattern “(^|\s)(\S)”. It looks for string patterns that starts with zero or more whitespaces and then has a non whitespace character after that. Then for each matching instance, it grouped both initial whitespaces and the first character as separate groups. Using regex.sub() function, we passed each matching instance of the pattern to a function convert_to_uppercase(), which converts the second group i.e. first letter of word to upper case and then joins it with the first group(zero or more white spaces).

For string,

sample_text = "it's gone tOO far"

The function convert_to_uupercase() was called 4 times by regex.sub() and in each call group 1 & 2 of match object were,

'' and 'i'
' ' and 'g'
' ' and 't'
' ' and 'f'

Inside convert_to_uupercase(), it converted the second group i.e. first character of each word to uppercase.

So, this is how we can capitalize the first letter of each word in a string using regex and without affecting any other character of the string.

The complete example is as follows,

import string
import re


def capitalize_each_word(original_str):
    result = ""
    # Split the string and get all words in a list
    list_of_words = original_str.split()
    # Iterate over all elements in list
    for elem in list_of_words:
        # capitalize first letter of each word and add to a string
        if len(result) > 0:
            result = result + " " + elem.strip().capitalize()
        else:
            result = elem.capitalize()
    # If result is still empty then return original string else returned capitalized.
    if not result:
        return original_str
    else:
        return result


def main():

    print('*** capitalize the first letter of each word in a string ***')

    print('*** Use title() to capitalize the first letter of each word in a string ***')

    print('Example 1:')
    sample_text = "this is a sample string"
    # Capitalize the first letter of each word i.e.
    # Convert the first letter of each word to Upper case and all other to lower case
    result = sample_text.title()

    print(result)

    print('Example 2:')

    sample_text = "33a. it's GONE too far"

    # Capitalize the first letter of each word
    result = sample_text.title()

    print(result)

    print('*** Use capitalize() to capitalize the first letter of each word in a string ***')

    sample_text = "33a. it's GONE too far"

    result = capitalize_each_word(sample_text)

    print(result)

    print('Using capitalize() and generator expression')

    result = ' '.join(elem.capitalize() for elem in sample_text.split())

    print(result)

    print('Example 2:')

    sample_text = "this     is       a      sample   string"

    result = ' '.join(elem.capitalize() for elem in sample_text.split())

    print(result)

    print('*** Using string.capwords() to capitalize the first letter of each word in a string ***')

    sample_text = "it's gone tOO far"

    result = string.capwords(sample_text)

    print(result)

    print('*** Using Regex to capitalize the first letter of each word in a string ***')

    sample_text = "it's gone   tOO far"

    result = re.sub("(^|\s)(\S)", convert_to_uupercase, sample_text)

    print(result)

def convert_to_uupercase(m):
    """Convert the second group to uppercase and join both group 1 & group 2"""
    return m.group(1) + m.group(2).upper()

if __name__ == '__main__':
    main()

Output:

*** capitalize the first letter of each word in a string ***
*** Use title() to capitalize the first letter of each word in a string ***
Example 1:
This Is A Sample String
Example 2:
33A. It'S Gone Too Far
*** Use capitalize() to capitalize the first letter of each word in a string ***
33a. It's Gone Too Far
Using capitalize() and generator expression
33a. It's Gone Too Far
Example 2:
This Is A Sample String
*** Using string.capwords() to capitalize the first letter of each word in a string ***
It's Gone Too Far
*** Using Regex to capitalize the first letter of each word in a string ***
It's Gone   TOO Far