[Python] getting string between 2 characters in python

I need to get certain words out from a string in to a new format. For example, I call the function with the input:

text2function('$sin (x)$ is an function of x')


and I need to put them into a StringFunction:

StringFunction(function, independent_variables=[vari])


where I need to get just 'sin (x)' for function and 'x' for vari. So it would look like this finally:

StringFunction('sin (x)', independent_variables=['x']


problem is, I can't seem to obtain function and vari. I have tried:

start = string.index(start_marker) + len(start_marker)
end = string.index(end_marker, start)
return string[start:end]


and

r = re.compile('$()$')
m = r.search(string)
if m:
lyrics = m.group(1)


and

send = re.findall('$([^"]*)$',string)


all seems to seems to give me nothing.

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