Question

The Python docs say:

re.MULTILINE: When specified, the pattern character ‘^’ matches at the beginning of the string and at the beginning of each line (immediately following each newline)… By default, ‘^’ matches only at the beginning of the string…

So what’s going on when I get the following unexpected result?

>>> import re >>> s = '''// The quick brown fox. ... // Jumped over the lazy dog.''' >>> re.sub('^//', '', s, re.MULTILINE) ' The quick brown fox.\n// Jumped over the lazy dog.' 

Answer 1

Look at the definition of re.sub:

re.sub(pattern, repl, string[, count, flags]) 

The 4th argument is the count, you are using re.MULTILINE (which is 8) as the count, not as a flag.

Either use a named argument:

re.sub('^//', '', s, flags=re.MULTILINE) 

Or compile the regex first:

re.sub(re.compile('^//', re.MULTILINE), '', s)