Regex not matching what it should

Question

I have a simple problem using Regex with python...

I am trying to grab GPS coordinates out of a line that will be formatted as such:

-73209460,44477974

Sometimes it will have the leading '-', sometimes it wont. Consequently, my regex is as follows:

'-?\d\d\d\d\d\d\d\d,\d\d\d\d\d\d\d\d'

Here's the weird part:

I have tested this query on solely the GPS coordinate string (above) and it works fine, matches it, and acts as intended. However when I try to get it to match the GPS coords when there is "noise" around it, it does not catch it... Here is one line that the GPS coords are in:

RoutingRequest,1391101299,3,-10,1,-1,1000,-73209460,44477974,-1,56862713,56862712,

Any idea why it would not be catching this? Something to do with the commas?

Thanks guys.

EDIT:

Thanks for all the responses... Here is a quick test script that I was using:

import re

def doesntWork():
    gpsCoords = r'-?\d\d\d\d\d\d\d\d,\d\d\d\d\d\d\d\d'
    gps = re.compile(gpsCoords)

    match = gps.match("1000,-73209460,44477974,-1,56862")

    if match:
        return True
    else:
        return False

def works():
    gpsCoords = r'-?\d\d\d\d\d\d\d\d,\d\d\d\d\d\d\d\d'
    gps = re.compile(gpsCoords)

    match = gps.match("-73209460,44477974")
    if match:
        return True
    else:
        return False

def main():
    print doesntWork()
    print works()

main()

Answer 1

Aside from the fact your regex looks a little fragile, this is likely due to using re.match instead of re.search .

re.match tries to match the regex to the beginning of your string, where as re.search tries to find a match anywhere in your string.

The difference is explained in the python documentation here: https://docs.python.org/3/library/re.html#search-vs-match

Answer 2

As SpoonMeiser said, you should be using re.search() . Here's a little more sophisticated regex which captures both lat and lon in named groups`.. Assuming the last values are longitude values.. This might break but it's a nice idea.

>>> r = "RoutingRequest,1391101299,3,-10,1,-1,1000,-73209460,44477974,-1,56862713,56862712"
>>> re.search(r"(?P<lat>-?\d{8},\d{8}).*(?P<lon>\d{8},\d{8})", r).groupdict()
{'lat': '-73209460,44477974', 'lon': '56862713,56862712'}