re.match versus re.findall

Question

Why is it, re.match returns the None object whilst a similar re.findall returns a non-empty result?

I'm parsing email subjects. The one in question is

subject = "=?UTF-8?B?0JLQsNGI0LUg0YHQvtC+0LHRidC10L3QuNC1INC90LUg0LTQvtGB0YLQsNCy0LvQtdC90L4=?=. Mail failure."

I'm wondering why

re.match("mail failure", subject, re.I) returns the None object whist the counterpart

re.findall("mail failure", subject, re.I) returns the matched string in a list ['Mail failure']

What is wrong in my thoughts?

Answer 1

re.match matches the pattern from the start of the string. re.findall however searches for occurrences of the pattern anywhere in the string.

If you have the pattern "mail failure" and the string:

subject = "=?UTF-8?B?0JLQsNGI0LUg0YHQvtC+0LHRidC10L3QuNC1INC90LUg0LTQvtGB0YLQsNCy0LvQtdC90L4=?=. Mail failure."

re.match will return None because the string does not start with "mail failure". re.findall though will return a match because the string contains "mail failure".

Answer 2

It's right here in the docs: https://docs.python.org/2/library/re.html What you want is re.search.

Note that even in MULTILINE mode, re.match() will only match at the beginning of the string and not at the beginning of each line.