What is a clean way to convert a string percent to a float?

Use strip('%') , as:

In [9]: "99.5%".strip('%')
Out[9]: '99.5'               #convert this to float using float() and divide by 100


In [10]: def p2f(x):
    return float(x.strip('%'))/100
   ....: 

In [12]: p2f("99%")
Out[12]: 0.98999999999999999

In [13]: p2f("99.5%")
Out[13]: 0.995

float(stringPercent.strip('%')) / 100.0