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?