Odtnhj

I'm pretty new to python and just learning how to debug and test my code.
We had to write a little BMI calculator for our course. However, if I try to run it with the tests I get the error:

Please enter only non-negative numbers.
Failure <Click to see difference>

**********************************************************************
File "C:/Users/TAGI/PycharmProjects/703410_U7_Tests/Programs/BMI/task.py", line 39, in task.bmi
Failed example:
 bmi(-1, 200)
Expected:
 Please enter only non-negative numbers.
Got:
 Please enter only non-negative numbers.
 -0.25

Why is it still calculating the result with the negative number after I raised the exception? If I comment my doctests out and try it without it works just fine. This is my code (with commented out doctests):

def check_variables(a):
 try:
 float(a)
 if a < 0:
 raise ValueError
 except ValueError:
 print("Please enter only non-negative numbers.")
 except:
 print("This is an error: something went wrong. Please try again.")
 return a


def bmi(a_weight, a_height):
 # TODO: write docstring for this function
 """
 This function returns the bmi of a person and tests the values. If they are invalid it returns an error.
 :param a_weight: a real number, the users weight
 :param a_height: a real number, the users height
 :return: bmi of user
 :rtype: float

 # >>> bmi(10,0)
 Traceback (most recent call last):
 ...
 ZeroDivisionError: float division by zero
 # >>> round(bmi(75,175), 1)
 24.5
 # >>> bmi("abc",177)
 Traceback (most recent call last):
 ...
 TypeError: unsupported operand type(s) for /: 'str' and 'float'
 # >>> bmi(0, 180)
 0.0
 # >>> bmi(-1, 200)
 Please enter only non-negative numbers.
 # >>> bmi(100, -40)
 Please enter only non-negative numbers.

 # TODO: write doctest for this function
 """
 return check_variables(a_weight) / (check_variables(a_height)/100) ** 2


bmi(-10, 180)