Problem with Series.str.match

[jseabold]

Not sure yet what's going on here. Doesn't appear to be a unicode issue

df = pandas.DataFrame([[u'A Confe\xdfion of the most auncient and true christen catholike olde belefe accordyng to the ordre of the .XII. Articles of our co[m]mon crede, set furthe in Englishe to the glory of almightye God, and to the confirmacion of Christes people in Christes catholike olde faith.']], columns=["title"])

df.title.str.match(".*[A|a]lmight")
# returns 
#0    ()
#Name: title

re.match(".*[A|a]lmight", df.title.ix[0])
# expected output
#<_sre.SRE_Match at 0x4fa8100>

[gerigk]

match searches only at the beginning of the string. I guess you are
expecting the behavior of re.search ?

re.match(pattern, string,
flags=0)http://docs.python.org/library/re.html#re.match

If zero or more characters at the beginning of string match the regular
expression pattern, return a corresponding
MatchObjecthttp://docs.python.org/library/re.html#re.MatchObject
instance.
Return None if the string does not match the pattern; note that this is
different from a zero-length match.

On Mon, Oct 15, 2012 at 10:21 PM, Skipper Seabold
[email protected]:

Not sure yet what's going on here. Doesn't appear to be a unicode issue

df = pandas.DataFrame([[u'A Confe\xdfion of the most auncient and true christen catholike olde belefe accordyng to the ordre of the .XII. Articles of our co[m]mon crede, set furthe in Englishe to the glory of almightye God, and to the confirmacion of Christes people in Christes catholike olde faith.']], columns=["title"])

df.title.str.match(".*[A|a]lmight")

returns

#0 ()
#Name: title

re.match(".*[A|a]lmight", df.title.ix[0])

expected output

#<_sre.SRE_Match at 0x4fa8100>

—
Reply to this email directly or view it on GitHubhttps://github.com//issues/2074.

[wesm]

The problem is that you have no groups in the regular expression:

In [16]: df.title.str.match("(.*[A|a]lmight)").ix[0]
Out[16]: (u'A Confe\xdfion of the most auncient and true christen catholike olde belefe accordyng to the ordre of the .XII. Articles of our co[m]mon crede, set furthe in Englishe to the glory of almight',)

A better behavior in the case where match.groups() is empty is to use match.group(0) if it exists

[jseabold]

I showed the expected behavior of re.match in the code example. That's why I stuck the .* at the beginning. What am I missing?

[wesm]

Well, if you look at the implementation of str.match, you see it unpacks the matched groups from the SRE_Match object. That is the issue

[jseabold]

Ah, I expected it to return something I can evaluate to True/False to make an index. Will adjust expectations.

[wesm]

Very open to API improvements here...put all those functions together over the course of about a day or so

[jseabold]

It's (sort of) clear in the documentation that it finds groups but I find myself right now just wanting to know if something matches rather than to pull out the groups. I can see use cases for both though.

[cpcloud]

you could have a matches method

[jreback]

@jseabold this new method might work for you

#4685