lambda_function.py

import re

def lambda_handler (event, context):
    
    return { 
        #'calculation' : eval(event) Did not choose to go with eval so there's better security on Server side
        'calculation' : evaluate(event)
    }  
    
def is_number(str):
    try:
        int(str)
        return True
    except ValueError:
        return False
 
def peek(stack):
    return stack[-1] if stack else None
 
def apply_operator(operators, values):
    operator = operators.pop()
    right = values.pop()
    left = values.pop()
    values.append(eval("{0}{1}{2}".format(left, operator, right)))
 
def greater_precedence(op1, op2):
    precedences = {'+' : 0, '-' : 0, '*' : 1, '/' : 1}
    return precedences[op1] > precedences[op2]
 
def evaluate(expression):
    tokens = re.findall("[+/*()-]|\d+", expression)
    values = []
    operators = []
    for token in tokens:
        if is_number(token):
            values.append(int(token))
        elif token == '(':
            operators.append(token)
        elif token == ')':
            top = peek(operators)
            while top is not None and top != '(':
                apply_operator(operators, values)
                top = peek(operators)
            operators.pop() 
        else:
            top = peek(operators)
            while top is not None and top not in "()" and greater_precedence(top, token):
                apply_operator(operators, values)
                top = peek(operators)
            operators.append(token)
    while peek(operators) is not None:
        apply_operator(operators, values)
 
    return values[0]