How to take a function as an argument? (Python)

Question

I'm writing a program to calculate the volume of a solid of rotation. The first step of this is to calculate an integral. I'm using scipy.integrate for this, but I can't figure out the best way to have a equation (like x=x**2 input at the command line. I was originally planning on adding an argument 'with respect to: x|y' and then taking the function as a lambda. Unfortunately, argparse won't take lambda as an argument type, and trying to use a string to construct a lambda (f = lambda x: args.equation) just returns a string (understandably really).

Here's what I've got so far:

import sys
import argparse
import math
from scipy import integrate

parser = argparse.ArgumentParser(description='Find the volume of the solid of rotation defined')
parser.add_argument('equation', help='continous function')
parser.add_argument('a', type=float, help='bound \'a\'')
parser.add_argument('b', type=float, help='bound \'b\'')
parser.add_argument('-axis', metavar='x|y', help='axis of revolution')
args = parser.parse_args()

def volume(func, a, b, axis=None):
  integral = integrate.quad(func, a, b)
  return scipy.py * integral

print volume(args.equation, args.a, args.b)

Any advice will be appreciated thanks

Answer 1

If there are absolutely no concerns about security risks from letting the user run arbitrary Python code, then you can use eval to create a callable object:

volume(eval('lambda x: %s' % args.equation), args.a, args.b)

Answer 2

You should be able to use eval() on the string you get from your arguments:

>>> f = eval("lambda x: x**2")
>>> f(5)
25