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I am trying to find the index of the reference in a list of references. Let me illustrate:

This is a list of references I scraped off a website:

ref = "<p class="references" style="font-size:15px">1. Mcminn. (2003). Last's Anatomy. Elsevier Australia. ISBN:0729537528. <a href="http://books.google.com/books?vid=ISBN0729537528">Read it at Google Books</a> - <a href="http://www.amazon.com/gp/product/0729537528">Find it at Amazon</a><br>

2. Netter, F. H. (2019). Atlas of human anatomy. Philadelphia, PA: Elsevier.</p>"

I thought I could get the index of reference (i.e. "1." and "2.") by using this:

result = list(map(int, [e for e in re.split("[^0-9]", ref) if e != '']))

But I'm getting all numbers: [1, 2003, 729537528, 2, 2019]

How do I only get the list of reference index, i.e. [1, 2] One way I guess is to find numbers followed by a dot, but I don't know how.

You may use

list(map(int, re.findall(r"(?<![^s>])([0-9]+). ", ref)))

See Python demo:

import re

p_text="""ref = <p class="references" style="font-size:15px">1. Mcminn. (2003). Last's Anatomy. Elsevier Australia. ISBN:0729537528. <a href="http://books.google.com/books?vid=ISBN0729537528">Read it at Google Books</a> - <a href="http://www.amazon.com/gp/product/0729537528">Find it at Amazon</a><br>

2. Netter, F. H. (2019). Atlas of human anatomy. Philadelphia, PA: Elsevier.</p>"""

result = list(map(int, re.findall(r"(?<![^s>])([0-9]+). ", p_text)))

print(result) # => [1, 2]

Details

• 
  (?<![^s>]) - a negative lookbehind that fails the match if, immediately to the left of the current location, there is a char other than whitespace and >
  


• 
  ([0-9]+) - Group 1: one or more digits (it will be the output value from re.findall)


• 
  . - a . and a space (replace the regular space with s to match any whitespace).

See the regex demo.

You can try this:

import re

o = re.findall(r'[>|s](d{1}).', ref)

print(o)

Will output:

['1', '2']

You might need to define a bit more structure, because just number (digit captured by d) and dot will also capture '8.' at the end of the ISBN number: ISBN:0729537528. Here I used a few characters that (in this example) help distinguishing the two cases. One reference is preceded by a '>' the other one by a space (s).

You have to "escape" the period so something like "[0-9]*." should work. That's off the top of my head so it may be slightly wrong; I'll also leave it up to you to figure out why * is there.

Be aware that Regex expressions in Python are slightly different from other implementations. For definitive info see:

See : https://docs.python.org/3/library/re.html

which suggests that you should start here:

https://docs.python.org/3/howto/regex.html#regex-howto

Here's the relevant section of the library page (about 1/ 3 the way down):

The special sequences consist of '' and a character from the list below. If the ordinary character is not an ASCII digit or an ASCII letter, then the resulting RE will match the second character. For example, $ matches the character '$'.

For the eqivalent python 2.x page change the version selector found at the top left corner of the page.