Most common "startswith" in a file to infer comment char

user_651174 0
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I am trying to determine what comment character a file may be using. For example:

site,rank
#alexa.com/rankings
google.com,1
yahoo.com,2

Is there a way to get the most comment "startswith" path in a list, and intersect that with a set of possible comment characters? What I'm doing now is the following, but it seems quite naive:

POSSIBLE_COMMENT_CHARS = ['#', '//', '/*', '*/']

def get_comment_char(file):
    with open(file) as f:
        for line in f:
            for _char in POSSIBLE_COMMENT_CHARS:
                if line.startswith(_char):
                    return _char

With the above file data it would return:

get_comment_char(myalexafile)
>>> #
python-3.x collections python
2 Answers

I would match the start of the lines with a combination of your comment strings, then count the occurrences.

And finally compute the string with the max number of occurrences

text="""
site,rank
#alexa.com/rankings
google.com,1
#yahoo.com,2
//whatever
# another comment

"""

import collections,re

POSSIBLE_COMMENT_CHARS = ['#', '//', '/*', '*/']

c = collections.Counter(re.findall("^({})".format("|".join(re.escape(x) for x in POSSIBLE_COMMENT_CHARS)),
     text,flags=re.MULTILINE))

print(max(c,key=lambda k: c.get(k)))

prints #

be careful with "|".join(re.escape(x) for x in POSSIBLE_COMMENT_CHARS in the general case because it implies a linear search. If you have 5000 strings in your list it can be quite slow. Here it's ok.

user_64515730

You could use a Counter and a regex:

from collections import Counter
import re 

with open(fn) as f: 
    c=Counter(m.group(1) for line in f for m in re.finditer(r'^\s*(#|//|/\*|\*/)', line))

>>> c
Counter({'#': 1})
user_2986070
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