Use string as input to re.compile

Question

I want to use a variable in a regex, like this:

variables = ['variableA','variableB']

for i in range(len(variables)):
    regex = r"'('+variables[i]+')[:|=|\(](-?\d+(?:\.\d+)?)(?:\))?'"
    pattern_variable = re.compile(regex)
    match = re.search(pattern_variable, line)

The problem is that python adds an extra backslash character for each backslash character in my regex string (ipython), and makes my regex invalid:

In [76]: regex
Out[76]: "'('+variables[i]+')[:|=|\\(](-?\\d+(?:\\.\\d+)?)(?:\\))?'"

Any tips on how I can avoid this?

Answer 1

There is no problem there. What you're seeing is the output of the repr() of the string. Since the repr is supposed to be more-or-less reversible back into the original object, it doubles up all backslashes, as well as escaping the type of quote used at the ends of the repr.

Answer 2

No, it only displays extra backslashes so that the string could be read in again and have the correct number of backslashes. Try

print regex

and you will see the difference.