I'm trying to write a calculator - python-3.x

Question

This is what happens exactly in Mac Terminal:
Enter command to calculate:
+,-,* or/:
after typing the command it asks me for num1 and num2:
type first number: 5
type second number: 5
then it asks me:
do you want to continue?
I type 'yes', the program starts all over again. Now the problem is,
the second time I do a calculation, it doesnt ask me if I want to continue, but it jumps straight to:
Enter command to calculate:
+,-,* or/:
or sometimes:
type first number: 5
type second number: 5
Why does that happen? and how can I make the program ask me every time if I want to continue after each calculation?
loop = True
while loop:
def func():
usr = input('''Enter command to calculate:
+,-,* or/:
''')
if usr not in ("+,-,*,/"):
print("Error! command not allowed. Try again")
func()
num1 = float(input("type first number: "))
num2 = float(input("type second number: "))
if usr == "+":
print("{0} + {1} = {r:0.2f}".format(num1,num2,r=num1+num2))
elif usr == "-":
print("{0} - {1} = {r:0.2f}".format(num1,num2,r=num1-num2))
elif usr == "*":
print("{0} * {1} = {r:0.2f}".format(num1,num2,r=num1*num2))
elif usr == "/":
print("{0} / {1} = {r:0.2f}".format(num1,num2,r=num1/num2))
def func2():
x = input("do you want to continue? ")
if x == "yes":
func()
elif x == "no":
exit()
else:
print("That was not clear. Try again: ")
func2()
func()
func2()

Answer 1

Do you know what I should do in this case?
Depends on what you aim at and what exactly you want to make.
Here's the easiest way to make a powerful console calculator, but at the same time the most insecure:
import os
import sys
import math
def main(argv = sys.argv):
print("EVAL Calculator\nType 'exit' to exit\n")
while True:
exp = input("Type a mathematical expression and press ENTER: ")
if exp.lower() == "exit": return
else: print(eval(exp))
if __name__ == "__main__":
main()
Input: 2 + 2 * 2
Output: 6
If this doesn't work for you, you can just split a string or use regular expressions.
If you just want to get your code to work well, move while True to the end of the code and tabulate the code itself.
It is not recommended to use the above code for those projects that are intended to be used by other people.