[FIXED] Filtering a list by regex in python does not work with single quotes

Issue

I am extracting data from a html page with xpath and want to retrieve a specific information located in a text part.

>>> response.xpath('//*[@id="productDetails"]/div[1]/div[2]/div[2]/text()').extract()
['\nInhalt: 10 Stück', '\nGrundpreis: 1 Stück 0,14 €']

This returns me the wanted info within a dictionary, alongside with several other info.

Now I try to grab the wanted info via regex, as I do not know the position, it changes. So I filter:

>>> r = re.compile('.*Grundpreis.*')
>>> newlist = list(filter(r.match, data))

Somehow this does not work and returns an empty list:

>>> newlist
[]

I followed examples found on SO which worked but this one does not. The only difference I could find is, that my example is single quotes instead of double quotes. But this seems not to be possible to change with the xpath command.

How can I extract the wanted information "Grundpreis:..." without a key index?

Solution

From the list of special characters in the syntax section of the re docs:

. (Dot.) In the default mode, this matches any character except a newline. If the DOTALL flag has been specified, this matches any character including a newline.

The Pattern.match() method:

If zero or more characters at the beginning of string match this regular expression, return a corresponding match object. Return None if the string does not match the pattern; note that this is different from a zero-length match.

Since the pattern .*Grundpreis.* will not match the first character of the string "\nGrundpreis: 1 Stück 0,14 €", as it is a newline, match() returns None.

---

Here is an example which should give you some inspiration for what you're trying to do:

import re

patt = re.compile(r"Grundpreis: (.*)")

test_strs = ['\nInhalt: 10 Stück', '\nGrundpreis: 1 Stück 0,14 €']

for elem in test_strs:
    res = patt.search(elem)
    if res:
        print(f"Match found in string: {elem}. Match: {res}. Group: {res.group(1)}")
    else:
        print(f"No match in string: {elem}")

Output:

No match in string: 
Inhalt: 10 Stück
Match found in string: 
Grundpreis: 1 Stück 0,14 €. Match: <re.Match object; span=(1, 27), match='Grundpreis: 1 Stück 0,14 €'>. Group: 1 Stück 0,14 €

Answered By - AMC