Python regex match whole string only

Question

Is there any easy way to test whether a regex matches an entire string in Python? I thought that putting $ at the end would do this, but it turns out that $ doesn't work in the case of trailing newlines.

For example, the following returns a match, even though that's not what I want.

re.match(r'\w+$', 'foo\n')

Answer 1

You can use \\Z :

\\Z

Matches only at the end of the string.

In [5]: re.match(r'\w+\Z', 'foo\n')

In [6]: re.match(r'\w+\Z', 'foo')
Out[6]: <_sre.SRE_Match object; span=(0, 3), match='foo'>

Answer 2

You can use a negative lookahead assertion to require that the $ is not followed by a trailing newline:

>>> re.match(r'\w+$(?!\n)', 'foo\n')
>>> re.match(r'\w+$(?!\n)', 'foo')
<_sre.SRE_Match object; span=(0, 3), match='foo'>

re.MULTILINE is not relevant here; OP has it turned off and the regex is still matching. The problem is that $ always matches right before the trailing newline :

When [ re.MULTILINE is] specified, the pattern character '^' matches at the beginning of the string and at the beginning of each line (immediately following each newline); and the pattern character '$' matches at the end of the string and at the end of each line (immediately preceding each newline). By default, '^' matches only at the beginning of the string, and '$' only at the end of the string and immediately before the newline (if any) at the end of the string.

I have experimentally verified that this works correctly with re.X enabled.

Answer 3

To test whether you matched the entire string, just check if the matched string is as long as the entire string:

m = re.match(r".*", mystring)
start, stop = m.span()
if stop-start == len(mystring):
    print("The entire string matched")

Note: This is independent of the question (which you didn't ask) of how to match a trailing newline.

Answer 4

Based on @alexis answer: A method to check for a fullMatch could look like this:

def fullMatch(matchObject, fullString):
    if matchObject is None:
        return False
    start, stop = matchObject.span()
    return stop-start == len(fullString):

Where the fullString is the String on which you apply the regex and the matchObject is the result of matchObject = re.match(yourRegex, fullString)