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!!

score 0 · Accepted Answer · answered May 29 '13 at 16:11

0

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?

answered May 29 '13 at 16:11

Thanks so much. I created a wrapper class and added a getFormula method. It did what I wanted. :) Here's the code (Sorry about the formatting. not sure how to format it in a comment...): `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)` – Crystal May 29 '13 at 17:04
looks pretty good, my only suggestion would be that it is possibly dangerous to be `eval`ing code from a config file, but it really depends on how this code will be used. If it is just for you to use, it probably doesn't matter. If you will be releasing it for others to use, you might want to add a bit of verification to the `retString` before you `eval` it. – May 29 '13 at 17:19

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

1 Answers1