Basic calculator using break statements to control the logic

Question

Below is a simple calculator program in which I'm using break statements to control the logic. I was wondering if this is overkill on the break statements or is it OK.

while True:
 try:
 print("Choose operation(+ | - | * | / | Enter 'e' to exit)")
 op=input()
 if op!="+" and op!="-" and op!="*" and op!="/" and op!="e":
 print("Invalid input, you must choose an option from the menu.")
 break
 elif op=="e":
 break
 else:
 print(">")
 val1=float(input(val1))
 print(">")
 val2=float(input(val2))
 if op=="+":
 print("= ", val1+val2)
 elif op=="-":
 print("= ", val1-val2) 
 elif op=="*":
 print("= ", val1*val2)
 else:
 print("= ", val1/val2) 
 except ValueError: 
 print("Input must be numerical.") 
 break 
 except ZeroDivisionError:
 print("Dividing by zero is undefined.")
 break
exit()

• ferada: Welcome to Code Review! Your post looks fine, hope you get some good answers!

Answer 1

Choosing an Operation

You can use a dictionary, rather than if/elif/else statements to choose operations more cleanly:

from operator import add, sub, mul, truediv
OPERATIONS = {
 '+': add,
 '-': sub,
 '*': mul,
 '/': truediv
}
# if an operation is present
print(OPERATIONS['+'](1, 2))
3
# otherwise
print(OPERATIONS['%'](1, 2))
KeyError

Now, you can clean up your if statements, and get rid of most of your if op == checks:

op = input("Choose operation(+ | - | * | / | Enter 'e' to exit)\n").strip()
if op == 'e':
 print('Exiting')
 exit()
try:
 operation = OPERATIONS[op]
except KeyError:
 print(f"{op} was an invalid choice")
 break
~snip~
# This is how you'd use that operation, since it is a function
try:
 print(operation(val1, val2))
except ZeroDivisionError:
 print("Can't divide by zero!")

Choosing val1 and val2

I think you made a typo by mistake and the argument to input was supposed to be input('val1') and input('val2'). Either way, I think it might be a bit cleaner to add a function here. This makes it easier to wrap up the possible ValueErrors that could come from generating your values on bad input:

def get_input_values():
 """
 Parse numerical input into floats for calculator operations
 """
 values = []
 for i in range(2):
 print('>')
 # this gives some visual space for the user to break up
 # the prompt from the actual input
 val = float(input(f'val{i}: ')
 values.append(val)
 return value
# now you can do a try/except wrapping this function
# and unpack the result
try:
 val1, val2 = get_input_values()
except ValueError as e:
 print(e)
 exit()

You could even extend this to N values if you wanted to:

def get_input_values(N=2):
 ~snip~
 for i in range(N):
 # rest of function
try:
 values = get_input_values(5)
except ValueError as e:
 ~snip~

Adding a main function and __name__ guard

This will help wrap your code up into a single function that can be called/looped/etc. It's cleaner and, for larger programs, makes it easier to find what runs the code. Also, an if __name__ == "__main__" guard allows you to import items from this code without it executing:

# OPERATIONS still lives in global scope here
OPERATIONS = {
 '+': add,
 '-': sub,
 '*': mul,
 '/': truediv
}
def main():
 op = input("Choose operation(+ | - | * | / | Enter 'e' to exit)\n").strip()
 
 if op == 'e':
 print('Exiting')
 exit()
 try:
 operation = OPERATIONS[op]
 except KeyError:
 print(f"{op} was an invalid choice")
 break
 try:
 val1, val2 = get_input_values()
 except ValueError as e:
 print(e)
 exit()
 try:
 result = operation(val1, val2)
 except ZeroDivisionError:
 print("Can't divide by zero!")
 exit()
 else:
 print(result)
if __name__ == "__main__":
 # you can move your loop down here now
 while True:
 main()