Is there any way to use ConfigParser to evaluate formulas rather than interpolate strings?

Question

I'm using ConfigParser in python 2.7.5 to parse a configuration file. I would like to interpolate some values but treat them as integers rather than strings (i.e., do the calculations). Is this possible?

Here's how I'm doing it currently:

global constantValues

config = ConfigParser.ConfigParser()

# use ConfigParser to get values
config.read("filename")

for section in config.sections():
    if (section == "INT"):
        for option in config.options(section):
            constantValues[option] = config.getint(section, option)
    elif (section == "BOOL"):
        for option in config.options(section):
            constantValues[option] = config.getboolean(section, option)
    elif (section == "FLOAT"):
        for option in config.options(section):
            constantValues[option] = config.getfloat(section, option)
    else:
        for option in config.options(section):
            constantValues[option] = config.get(section, option)

constantValues["samp_per_clk"] = int (constantValues["fs"] / constantValues["sys_clk"])
constantValues["samp_per_trig"] = float(constantValues["fs"] / constantValues["sys_clk"] * constantValues["clks_per_enc"])

I'd like to calculate "samp_per_clk" and "samp_per_trig" in the config file and then use the configparser to read it in. Something like this:

samp_per_clk: %(fs) / %(sys_clk)

But everything I've read seems to say you can only interpolate with strings. Am I missing anything?

EDIT: Based on Paul Woolcock's answer below, and the answer to this question, I added the following wrapper class:

class myConfigParser(object):
    def __init__(self, origobj):
        self.myobj = origobj
    def getFormula(self, section, option):
        retString = self.get(section, option)
        return eval(retString)
    def __getattr__(self, attr):
        return getattr(self.myobj, attr)

That did the trick!!

Answer 1

Out of the box, no, you can't do this with ConfigParser. However, ConfigParser.ConfigParser is just a class, and classes are overrideable :). I see no reason why you couldn't write a class FormulaConfigParser(ConfigParser) that overrides ConfigParser.get() to implement this behaviour, or perhaps adds a .getformula() method?