How can I capitalize the first letter of each word in a string?

The .title() method of a string (either ASCII or Unicode is fine) does this:

>>> "hello world".title()'Hello World'>>> u"hello world".title()u'Hello World'

However, look out for strings with embedded apostrophes, as noted in the docs.

The algorithm uses a simple language-independent definition of a word as groups of consecutive letters. The definition works in many contexts but it means that apostrophes in contractions and possessives form word boundaries, which may not be the desired result:

>>> "they're bill's friends from the UK".title()"They'Re Bill'S Friends From The Uk"

The .title() method can't work well,

>>> "they're bill's friends from the UK".title()"They'Re Bill'S Friends From The Uk"

Try string.capwords() method,

import stringstring.capwords("they're bill's friends from the UK")>>>"They're Bill's Friends From The Uk"

From the Python documentation on capwords:

Split the argument into words using str.split(), capitalize each word using str.capitalize(), and join the capitalized words using str.join(). If the optional second argument sep is absent or None, runs of whitespace characters are replaced by a single space and leading and trailing whitespace are removed, otherwise sep is used to split and join the words.

Just because this sort of thing is fun for me, here are two more solutions.

Split into words, initial-cap each word from the split groups, and rejoin. This will change the white space separating the words into a single white space, no matter what it was.

s = 'the brown fox'lst = [word[0].upper() + word[1:] for word in s.split()]s = " ".join(lst)

EDIT: I don't remember what I was thinking back when I wrote the above code, but there is no need to build an explicit list; we can use a generator expression to do it in lazy fashion. So here is a better solution:

s = 'the brown fox's = ' '.join(word[0].upper() + word[1:] for word in s.split())

Use a regular expression to match the beginning of the string, or white space separating words, plus a single non-whitespace character; use parentheses to mark "match groups". Write a function that takes a match object, and returns the white space match group unchanged and the non-whitespace character match group in upper case. Then use re.sub() to replace the patterns. This one does not have the punctuation problems of the first solution, nor does it redo the white space like my first solution. This one produces the best result.

import res = 'the brown fox'def repl_func(m):    """process regular expression match groups for word upper-casing problem"""    return m.group(1) + m.group(2).upper()s = re.sub("(^|\s)(\S)", repl_func, s)>>> re.sub("(^|\s)(\S)", repl_func, s)"They're Bill's Friends From The UK"

I'm glad I researched this answer. I had no idea that re.sub() could take a function! You can do nontrivial processing inside re.sub() to produce the final result!