Matching an empty string with regex

Question

I\'ve seen posts here on stackoverflow that say that the regex ^$ will match an empty string... So it made me think... why not something like this: ^\\s+$

Answer 1

\s is the character class for whitespace. ^\s+$ would match both "\t\n" and "\t\t". They look empty, but are not. Spaces, tabs, and newlines are characters too! By using ^$, you match the beginning of the string with ^ immediately followed by the end of the string $. Note that matching the regular expression '' will also match empty strings, but match them anywhere.

Python example:

empty_string_matches = re.findall('', 'hello world')
empty_line_matches = re.findall('^$', 'hello world')
print "Matches for '':", empty_string_matches
print "Matches for '^$':", empty_line_matches

returns

Matches for '': ['', '', '', '', '', '', '', '', '', '', '', '']
Matches for '^$': []

Because there is an empty string between each letter in 'hello world'.