In Python, why is this negative float passing the non-negative while loop test condition?

• Working in Python
• Collecting user input
• Input needs to be non-negative
• Successfully used While condition in another part of program
• But now don’t understand why this test to capture valid input is failing.

print("How many grams of xyz are required?")
xyz_string = input()
xyz = int(float(xyz_string))
while xyz < 0:
     print("Sorry, the amount must be a non-negative number. Please try again.")
     print("How many grams of xyz are required")
     xyz_string = input()
     xyz = int(float(xyz_string))
all_xyz.append(xyz)

When testing, I entered:

-0.8

I expected this to fail the non-negative test.
But it didn’t, and the invalid input exited the While Loop, and appended the invalid input.

Any assistance is appreciated.

>Solution :

The problem is the expression int(float(xyz_string)). This rounds all your numbers towards zero, so if the number you entered is between 0 and -1, it will be rounded up to zero and pass the test.

To fix this, just delay your int calls until after you’re done getting input:

print("How many grams of xyz are required?")
xyz_string = input()
xyz = float(xyz_string)
while xyz < 0:
     print("Sorry, the amount must be a non-negative number. Please try again.")
     print("How many grams of xyz are required")
     xyz_string = input()
     xyz = float(xyz_string)
all_xyz.append(int(xyz))