lwcalc2.py

from operator import * 
lookup = { '-': sub, '+': add, '*': mul, '/': truediv, '^': pow}
def lwe(e):
    for ops in ['+-', '/*', '^']:            
        i = max([e.rfind(c) for c in ops])
        if i != -1: return lookup[e[i:i+1]](lwe(e[:i]), lwe(e[i+1:]))
    return float(expr)
print(lwe(input("> ")))