How to calculate the BMI with python

Question

I have to make a script that calculate the BMI with a function that can accept only 2 arguments (those arguments can't be str or bool of course...)! + I have to use "{}.format()" in it but I don't know how!

BMI= height/weight**2

import sys

#if the script has been given 2 arguments, he continues, if not(=else) he print a message
if len(sys.argv) == 3:

#The first argument should be the height and the second one should be the weight
height=sys.argv[1]
weight=sys.argv[2]

    def bmi (height,weight):

        bmi=(height/weight**2)

        if type(height) is float and type(weight) is int:
        res=print("your bmi is {}".format(bmi))

        else:
        res=print(" height should be a float and weight an int")

    return(res)

else:
    print("you should enter 2 arguments")

I have no response from python...

Indenting is important with python. Make sure you indent the code you have under the `if/else`, use `isinstance(hieght, float)`, don't use `type`, lastly `print` outputs to terminal but returns nothing so you can't do `res = print('foo')` because `res` will be `None`. — Error - Syntactical Remorse, Oct 27 '19 at 19:26

JohanC · Answer 1 · 2019-10-27T20:59:23.453

Be very careful with indentation, as Python code depends very strong on it.

The print() function doesn't return a result. It just prints out what you ask it.

Also, be careful with executing the line bmi=(height/weight**2) before you checked the validity of height and weight. Best wait until you checked them. Otherwise, Python would write out a cryptic error about these types.

A function is not executed when you define it. You should add a call to the function bmi() you defined, as in:

import sys

def bmi (height,weight):
    return height/weight**2


#if the script has been given 2 arguments, he continues, if not(=else) he print a message
if len(sys.argv) == 3:

    #The first argument should be the height and the second one should be the weight
    height=float(sys.argv[1])  # argv[1] is a string and should be converted to float
    weight=int(sys.argv[2])    # argv[2] is a string and should be converted to int

    if type(height) is float and type(weight) is int:
        print("your bmi is {}".format(bmi(height,weight)))
            # "bmi()" calls the bmi function
    else:
        print(" height should be a float and weight an int")
else:
    print("you should enter 2 arguments")

Although Python allows to define functions anywhere in your code, it is best to separate such functions. isinstance() is normally preferred to type() == because isinstance() also checks for subclasses.

edit: added conversions from string to int/float as indicated by Patrick Artner

PS: Check out Checking if a string can be converted to float in Python for information about better checking whetter a string is a valid float. This would mean following adaption to the code:

    try:
        height=float(sys.argv[1])  # argv[1] is a string and should be converted to float
        weight=int(sys.argv[2])    # argv[2] is a string and should be converted to int
    except ValueError:
        print(" height should be a float and weight an int")

will never work in python 3 - sys.argv does not give you ints or floats ... — Patrick Artner, Oct 27 '19 at 20:00

How to calculate the BMI with python

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