Default parameter value instead globals

defparamval.py

# Instead of defining a global to use inside your function, just define it as a default
# value of the function, specially if the value can cost some significant time

regex = re.compile('[^0-9]') # globals are evil (are they?)
def clean_zip(string):
    return regex.sub('', string)

# This way we execute re.compile a single time AND have the advantage to overwrite it when necessary

def clean_zip(string, regex=re.compile('[^0-9]')):
    return regex.sub('', string)