All I need is to check, using python, if a string is a valid math expression or not.
For simplicity let\'s say I just need + - * /
operators (+ -
Why not just evaluate it and catch the syntax error?
from math import *
def validateSyntax(expression):
functions = {'__builtins__': None}
variables = {'__builtins__': None}
functions = {'acos': acos,
'asin': asin,
'atan': atan,
'atan2': atan2,
'ceil': ceil,
'cos': cos,
'cosh': cosh,
'degrees': degrees,
'exp': exp,
'fabs':fabs,
'floor': floor,
'fmod': fmod,
'frexp': frexp,
'hypot': hypot,
'ldexp': ldexp,
'log': log,
'log10': log10,
'modf': modf,
'pow': pow,
'radians': radians,
'sin': sin,
'sinh': sinh,
'sqrt': sqrt,
'tan': tan,
'tanh': tanh}
variables = {'e': e, 'pi': pi}
try:
eval(expression, variables, functions)
except (SyntaxError, NameError, ZeroDivisionError):
return False
else:
return True
Here are some samples:
> print validSyntax('a+b-1') # a, b are undefined, so a NameError arises.
> False
> print validSyntax('1 + 2')
> True
> print validSyntax('1 - 2')
> True
> print validSyntax('1 / 2')
> True
> print validSyntax('1 * 2')
> True
> print validSyntax('1 +/ 2')
> False
> print validSyntax('1 + (2')
> False
> print validSyntax('import os')
> False
> print validSyntax('print "asd"')
> False
> print validSyntax('import os; os.delete("~\test.txt")')
> False # And the file was not removed
It's restricted to only mathematical operations, so it should work a bit better than a crude eval
.