A silly little script that evaluates command line mathematical expressions.

calc.py

#!/usr/bin/env python

"""A silly little script that evaluates command line mathematical expressions."""

from __future__ import division
import sys

if __name__ == '__main__':
	
	expression = ' '.join(sys.argv[1:])
	if len(expression) == 0:
		sys.exit("""
Enter a mathematical expression as the command line argument for this script.

Examples:

    python calc.py 2 + 5
    python calc.py 2 ** 5
    python calc.py 5 * (3 + 2)
    python calc.py 5 / 2

Note: by default, this script performs floating point division. 
For integer division, use a double-slash - // - instead of a single slash - / - in your expression.""")

	validchars = '0123456789 +-*/()=.'
	valid_expression = ''.join([c for c in expression if c in validchars])
        if valid_expression != expression:
		sys.exit('\nSorry, but "%s" is not a valid mathematical expression.' % (expression))
	print '\n%s = %s' % (valid_expression, eval(valid_expression))