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import re


" Math functions--------------------"
def plus(int1, int2):
    return float(int1 + int2)

def minus(int1, int2):
    return float(int1 - int2)

def multiply(int1, int2):
    return float(int1 * int2)

def square(int1, int2):
    return float(int1 ** int2)

def root(int1, int2):
    return float(int1 // int2)


" Main functions--------------------"
def get_operators(string):
    global oprt_plattern
    return re.findall(oprt_plattern, string)

def get_numbers(string):
    global numbers_plattern
    return re.findall(numbers_plattern, string)

def calculate(string):
    global operators
    global tmp_result
    string_numbers = get_numbers(string)
    string_operators = get_operators(string)

    result = int(string_numbers[0])
    string_numbers.pop(string_numbers.index(string_numbers[0]))

    for None_ in range(len(string_numbers)):
        result = operators[string_operators[0]] (result, int(
            string_numbers[0]))
        string_operators.pop(string_operators.index(string_operators[0]))
        string_numbers.pop(string_numbers.index(string_numbers[0]))
    return tmp_result
            

" Vars---------------------------------"
oprt_plattern = r"[+-/*(//)(**)]{1,}"
numbers_plattern = r"\d{1,}"

operators = {
    "+" : plus,
    "-" : minus,
    "*" : multiply,
    "**" : square,
    "//" : root,
    }

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print eval("45 * 9 - 9 + 2.3")

Code: Alles auswählen

import re

operators = {
    "+": lambda a, b: a + b,
    "-": lambda a, b: a - b,
    "*": lambda a, b: a * b,
    "/": lambda a, b: a / b,
    "**": lambda a, b: a ** b,
}

class Parser(object):
    def __init__(self, s):
        def scan(s):
            for m in re.finditer(r"(\d+)|(\*\*|[-+*/()])", s):
                yield m.group()
            yield ""
        self.scanner = scan(s)
        self.token = self.scanner.next()
    
    def advance(self):
        token, self.token = self.token, self.scanner.next()
        return token
    
    def eval(self):
        r = self.eval_factor()
        while self.token in ("+", "-"):
            r = operators[self.advance()](r, self.eval_factor())
        return r
    
    def eval_factor(self):
        r = self.eval_power()
        while self.token in ("*", "/"):
            r = operators[self.advance()](r, self.eval_power())
        return r
    
    def eval_power(self):
        r = self.eval_value()
        if self.token == "**":
            r = operators[self.advance()](r, self.eval_power())
        return r
    
    def eval_value(self):
        if self.token.isdigit():
            return int(self.advance())
        if self.token == "(":
            self.advance()
            r = self.eval()
            if self.advance() != ")": raise SyntaxError
            return r
        raise SyntaxError

print Parser("(3+4*5)**2").eval()

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        self.scanner = (m.group() for m in re.finditer(r"\d+|\*\*|[-+*/()]|", s))