python regex on variable

Question

Please help with my regex problem

Here is my string

source="http://www.amazon.com/ref=s9_hps_bw_g200_t2?pf_rd_m=ATVPDKIKX0DER&pf_rd_i=3421"
source_resource="pf_rd_m=ATVPDKIKX0DER"

The source_resource is in the source may end with & or with .[for example].

So far,

regex = re.compile("pf_rd_m=ATVPDKIKX0DER+[&.]")
regex.findall(source)
[u'pf_rd_m=ATVPDKIKX0DER&']

I have used the text here. Rather using text, how can i use source_resource variable with & or . to find this out.

I think i found out. Let me wait for other experts to give their idea pattern=re.compile( source_resource+'[&.]') — Sathy
– Sathy, Commented Jun 12, 2013 at 7:55
Yes that is (nearly) correct - just escape the . with a \ , because in regular-expressions a normal dot will match on any character, not just a dot. — BergmannF
– BergmannF, Commented Jun 12, 2013 at 8:02
@Sathy Does source_resource stay the same throughout the program? — Jared
– Jared, Commented Jun 12, 2013 at 8:08
@Jared it goes under a if-elif-else module which creates different source_resource against each condition satisfied — Sathy
– Sathy, Commented Jun 12, 2013 at 8:55

icecrime · Accepted Answer · 2013-06-12 07:59:40Z

3

If the goal is to extract the pf_rd_m value (which it apparently is as you are using regex.findall), than I'm not sure regex are the easiest solution here:

>>> import urlparse
>>> qs = urlparse.urlparse(source).query
>>> urlparse.parse_qs(qs)
{'pf_rd_m': ['ATVPDKIKX0DER'], 'pf_rd_i': ['3421']}
>>> urlparse.parse_qs(qs)['pf_rd_m']
['ATVPDKIKX0DER']

answered Jun 12, 2013 at 7:59

icecrime

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1 Comment

Sathy Over a year ago

thanks @icecrime. this is what I have done since my thought is pf_rd_m might change in future. source_resource=source.split('?')[1].split('&')[0] I always want the first value of my query, no matter what is assigned. Advise me if any better option

E.Z. · Accepted Answer · 2013-06-12 07:58:48Z

2

You also have to escape the .

pattern=re.compile(source_resource + '[&\.]')

answered Jun 12, 2013 at 7:58

E.Z.

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Comments

BergmannF · Accepted Answer · 2013-06-12 07:59:28Z

You can just build the string for the regular expression like a normal string, utilizing all string-formatting options available in Python:

import re
source_and="http://rads.stackoverflow.com/amzn/click/B0030DI8NA/pf_rd_m=ATVPDKIKX0DER&"
source_dot="http://rads.stackoverflow.com/amzn/click/B0030DI8NA/pf_rd_m=ATVPDKIKX0DER."
source_resource="pf_rd_m=ATVPDKIKX0DER"
regex_string = source_resource + "[&\.]"
regex = re.compile(regex_string)
print regex.findall(source_and)
print regex.findall(source_dot)
>>> ['pf_rd_m=ATVPDKIKX0DER&']
['pf_rd_m=ATVPDKIKX0DER.']

I hope this is what you mean.

Just take note that I modified your regular expression: the . is a special symbol and needs to be escaped, as is the + (I just assumed the string will only occur once, which makes the use of + unnecessary).

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