If else issue with python project

Question

import sys

n = len(sys.argv)

average = 0.0
value_1 = float(sys.argv[1])
value_2 = float(sys.argv[2])
value_3 = float(sys.argv[3])

if value_1 or value_2 or value_3 == str:
    print("Your input is invalid!")
else:
    total = value_1 + value_2 + value_3
    average = total / 3
    print("Average:%.2f" % average)

I tried using if else statement where if input is str it will display an error message however it is not working.

Your code doesn't really make sense - `float` would already raise an error if the input is inconvertible. — AKX, Sep 09 '22 at 14:13
If you want check the type of a value, it's `isinstance(x, y)`, not `x == y`. — chepner, Sep 09 '22 at 14:14
@chepner The duplicate is not applicable here, since OP's `if` statement doesn't make sense. — AKX, Sep 09 '22 at 14:14
It's applicable; it's just not *complete*. There are multiple issues here; we can add additional duplicates to cover the type-checking issue. — chepner, Sep 09 '22 at 14:14
(Even if the proper solution is to do away with multiple conditions, the OP is still under the mistaken assumption that `x or y or z == a` is the way to check if `x == a` or `y== a` or `z == a`.) — chepner, Sep 09 '22 at 14:16

AKX · Answer 1 · 2022-09-09T14:22:10.213

float would raise an error if it can't convert the input, so there's no point in checking things in an if statement afterwards.
You'd use ifinstance(x, str) to check if x is a string.
- Furthermore, to check for multiple conditions, you would need to repeat the entire "subcondition".
You're not using n for anything.

A version of your code that would have more correct error handling (catches both conversion errors and not having enough inputs) is

import sys

try:
    value_1 = float(sys.argv[1])
    value_2 = float(sys.argv[2])
    value_3 = float(sys.argv[3])
except (ValueError, IndexError):
    print("Your input is invalid!")
else:
    total = value_1 + value_2 + value_3
    average = total / 3
    print("Average:%.2f" % average)

A version that tries to convert any variable number of arguments:

import sys

try:
    values = [float(arg) for arg in sys.argv[1:]]
except ValueError:
    print("Your input is invalid!")
else:
    if not values:
        print("No input, can't compute average")
    else:
        total = sum(values)
        average = total / len(values)
        print("Average:%.2f" % average)

If else issue with python project

1 Answers1