Python regex doesn't find certain pattern

Question

I am trying to parse latex code from html code which looks like this:

string = " your answer is wrong! Solution: based on \((\vec{n_E},\vec{g})= 0 \) and \(d(g,E)=0\) beeing ... "

I want to replace all latex code with the output of a function that takes the latex code as an argument (Since there is a problem with finding the correct pattern, the function extract returns an empty string for the moment).

I tried:

latex_end = "\)"
latex_start = "\("    
string = re.sub(r'{}.*?{}'.format(latex_start, latex_end), extract, string)

Result:

your answer is wrong! Solution: based on \= 0 \) and \=0\) beeing ...

Expected:

your answer is wrong! Solution: based on and beeing ...

Any idea why it does not find the pattern? Is there a way to implement it?

Booboo · Accepted Answer · 2020-01-11 20:35:30Z

1

You should use a raw string for your definition of string since \v is being interpreted as a special character.

import re

string = r" your answer is wrong! Solution: based on \((\vec{n_E},\vec{g})= 0 \) and \(d(g,E)=0\) beeing ... "


string = re.sub(r'\\\(.*?\\\)', '', string))
print(string)

Prints:

 your answer is wrong! Solution: based on  and  beeing ...

If you need to have variables for the start and end:

latex_end = r"\\\)"
latex_start = r"\\\("    
string = re.sub(r'{}.*?{}'.format(latex_start, latex_end), '', string)
print(string)

answered Jan 11, 2020 at 20:35

Booboo

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Vadim · Accepted Answer · 2020-01-11 20:32:54Z

1

This is because of backslashes serving as escape characters in Python. This makes handling these kinds of situations very tricky. The following are two quick ways of making this work:

import re

extract = lambda a: ""

# Using no raw components
string = " your answer is wrong! Solution: based on \((\vec{n_E},\vec{g})= 0 \) and \(d(g,E)=0\) beeing ... "
latex_bounds = ("\\\(", "\\\)\)")
print(re.sub('{}.*?{}'.format(*latex_bounds), extract, string))

# Using all raw components (backslashes mean nothing, but not really)
string = r"%s" % string
latex_bounds = (r"\\\(", r"\\\)")
print(re.sub(r'{}.*?{}'.format(*latex_bounds), extract, string))

edited Jan 11, 2020 at 20:32

answered Jan 11, 2020 at 20:26

Vadim

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