Question

I am fairly new to python.

I have been asked to create a calculator using only string commands, conversions between int/string/float etc.(if needed), and using functions is a requirement. while and for loops can also be used.

The program needs to take an input of the form x/y or x/y/z, where x y z are any positive or negative number. Where “/” can be replaced by addition multiplication and subtraction as well. And where any number of white spaces can exist between operands and operators. This is an idea of what I have so far.

I would have a unique definition for +,-,/, and *. I would create a function for what the user inputs. I would use “.lstrip” and “.rstrip” to get rid of white spaces.

Now what I am having trouble with is creating the input function. I am very new to functions and this is basically what I have. I know it isn’t much to work with but I am really stuck on how to properly enter the function.

def multiplication(x,a,y,b,z):
    if (a== "*"):
        return x*y
    if (b== "*"):
        return y*z

def division(x,a,y,b,z):
    if (a== "/"):
        return x/y
    if (b== "/"):
        return y/z

def addition(x,a,y,b,z):
    if (a== "+"):
        return x+y
    if (b== "+"):
        return y+z

def subtraction(x,a,y,b,z):
    if (a== "-"):
        return x-y
    if (b== "-"):
        return y-z

def (x,y,z):
    x=0
    y=0
    z=0

    zxc=int(input()):# this is where I get stuck and I don't know how to implement x,y,z into the input.

All help is appreciated. If you are unsure of whether the code you provide is too intense for my needs, please ask before wasting your time for me, making code that I can’t possibly use. I promise to reply ASAP.

Basically I am trying to find a way to split the inputted string AND THEN start calculations with it.

Answer 1

Here is a possible solution outline using regular expressions. Error checking left as exercise. If this isn’t homework and you’d like to see the fleshed-out solution, view it here

import re

# input is a list of tokens (token is a number or operator)
tokens = raw_input()

# remove whitespace
tokens = re.sub('\s+', '', tokens)

# split by addition/subtraction operators
tokens = re.split('(-|\+)', tokens)

# takes in a string of numbers, *s, and /s. returns the result
def solve_term(tokens):
    tokens = re.split('(/|\*)', tokens)
    ret = float(tokens[0])
    for op, num in <FILL THIS IN>:
        # <apply the operation 'op' to the number 'num'>
    return ret

# initialize final result to the first term's value
result = solve_term(tokens[0])

# calculate the final result by adding/subtracting terms
for op, num in <FILL THIS IN>:
    result +=  solve_term(num) * (1 if op == '+' else -1)

print result