Web-Safe Arithmetic Expressions Evaluator
import math
import re
whitelist = '|'.join(
# oprators, digits
['-', '\+', '/', '\\', '\*', '\^', '\*\*', '\(', '\)', '\d+']
# functions of math module (ex. __xxx__)
+ [f for f in dir(math) if f[:2] != '__'])
valid = lambda exp: re.match(whitelist, exp)
>>> valid('23**2')
<_sre.SRE_Match object at 0xb78ac218>
>>> valid('sys.exit(100)') == None
True
>>> exp = '23**2'
>>> if valid(exp):
>>> x = eval(exp)
came across this post via unofficial planet python
