My beginner python project (calculator) is having trouble with inputs

Question

Whenever I test my calculator to see how it deals with inputs that are not numbers, it flags up a ValueError. More precisely, this one "ValueError: could not convert string to float: 'a'". I have tried to amend this so there is a solution to dealing with non-integers but to no avail... Help is much appreciated.

Here is my code so far:

print("1. ADDITION ")
print("2. MULTIPLICATION ")
print("3. TAKEAWAY ")
print("4. DIVISION ")

Operator = int(input("please enter one of the numbers above to decide the operator you want. "))

while Operator > 4:
    print("Please select a number from the options above. ")
    Operator = int(input("please enter one of the numbers above to decide the operator you want. "))
    if Operator != (1 or 2 or 3 or 4):
        print("please enter one of the options above. ")
        Operator = int(input("please enter one of the numbers above to decide the operator you want. "))
    continue

while True:
    Num1 = float(input("Please enter first number. "))
    if Num1 == float(Num1):
        print("thanks! ")
    elif Num1 != float(Num1):
        Num1 = float(input("Please enter first number. "))
    break

while True:
    Num2 = float(input("Please enter second number. "))
    if Num2 == float(Num2):
        print("thanks ")
    elif Num1 != float(Num1):
        Num1 = float(input("Please enter first number. "))
    break

You need to look into [`try/except`](https://docs.python.org/3/tutorial/errors.html#handling-exceptions) blocks. — Christian Dean, Sep 28 '16 at 12:38
...and the solution here will show you how: http://stackoverflow.com/questions/8420143/valueerror-could-not-convert-string-to-float-id — Topological Sort, Sep 28 '16 at 14:22

score 1 · Answer 1 · answered Sep 28 '16 at 12:38

1

Exception handling is what are you looking for. Smthng like this:

input = 'a'
try:
    int(a)
except ValueError:
    print 'Input is not integer'

answered Sep 28 '16 at 12:38

poko

575
2
8

score 0 · Answer 2 · answered Sep 28 '16 at 12:38

0

Please read the docs for handling exceptions:

https://docs.python.org/2/tutorial/errors.html#handling-exceptions

for a float:

try:
    x = float(input("Please enter a number: "))
    break
except ValueError:
    print "Oops!  That was no valid number.  Try again..."

answered Sep 28 '16 at 12:38

brunoelottero

80
1
7

Thanks brunoelottero! – Alex Bakic Sep 29 '16 at 16:00

score 0 · Answer 3 · edited May 23 '17 at 12:19

Note: You should name your variables in lower case according to PEP8, see: What is the naming convention in Python for variable and function names?.

If you want to retry an input until you don't get ValueError, put it in a loop:

print("Please select a number from the options above.")
while True:
    try:
        operator = int(input("please enter one of the numbers above to decide the operator you want: "))
    except ValueError:
        print("Sorry, not a number. Please retry.")
    else:
        if 1 <= operator <= 4:
            break
        else:
            print("Sorry, choose a value between 1 and 4.")

Note: use input with Python 3.x or raw_input with Python 2.7

1. ADDITION
2. MULTIPLICATION
3. TAKEAWAY
4. DIVISION
Please select a number from the options above.
please enter one of the numbers above to decide the operator you want: spam
Sorry, not a number. Please retry.
please enter one of the numbers above to decide the operator you want: 12
Sorry, choose a value between 1 and 4.
please enter one of the numbers above to decide the operator you want: 2

Your welcome. Have you solve your problem? Python is great, isn't it? — Laurent LAPORTE, Sep 29 '16 at 17:43

My beginner python project (calculator) is having trouble with inputs

3 Answers3