BMR calculator

#!/usr/bin/env python3
from sys import argv, exit

def getinput(question,t):
    inp = None
    while True:
        try:
            inp = t(input(question))
            return inp
        except KeyboardInterrupt:
            exit()
        except:
            print("please input the correct type")


def lbtokg(lb):
    return lb / 2.202

def inchtocm(inches):
    return inches * 2.540

def harris_male(weight,height,age):
    return 66+ 13.7*weight + 5*height - 6.8*age

def harris_female(weight,height,age):
    return 655 + 9.6*weight + 1.8*height - 4.7*age

def mifflin_male(weight,height,age):
    return 9.99*weight + 6.25*height - 4.92*age + 5

def mifflin_female(weight,height,age):
    return 9.99*weight + 6.25*height - 4.92*age - 161

def katch(LBM):
    return 370 + 21.6*LBM

def cunningham(LBM):
    return 500 + 22*LBM

def main(metric=None,sex=None,weight=None,height=None,age=None,bf=None):
    if metric == None:
        metric = getinput("Metric units? y for yes, n for no  ",str)
        if metric[0] == 'n' or metric[0] == 'N':
            metric = 0
        else: metric = 1
    if sex    == None:
        while sex not in ['m','M','f','F']:
            sex    = getinput("Are you a male or female? (m or f) ", str)
    if weight == None:
        weight = getinput("What is your weight?   ",float)
    if height == None:
        height = getinput("What is your height?   ",float)
    if age    == None:
        age    = getinput("What is your age?      ",float)

    if metric == 0:
        weight = lbtokg(weight)
        height = inchtocm(height)

    if bf==None:
        while True:
            bf     = input("Optional: What is your body fat? ")
            if bf == '':
                LBM=None
                break
            else:
                try:
                    LBM = weight * (1-(float(bf)/100))
                    break
                except:
                    print("please input it in correctly")
    elif bf == 0.0:
        LBM = None
    else:
        LBM = weight * (1-(bf/100))



    if sex[0] == 'm' or sex[0] == 'M':
        print("Harris-Benedict: ",harris_male(weight,height,age))
        print("Mifflin-St Jeor: ",mifflin_male(weight,height,age))
    elif sex[0] == 'f' or sex[0] == 'F':
        print("Harris-Benedict: ",harris_female(weight,height,age))
        print("Mifflin-St Jeor: ",mifflin_female(weight,height,age))
    if LBM:
        print("Katch-McArdle:   ",katch(LBM))
        print("Cunningham:      ",cunningham(LBM))


if __name__ == '__main__':
    if len(argv) != 1 and (argv[1] == '-h' or argv[1] == '--help'):
        print(\
"""
-w --weight   Set the weight
-h --height   Set the height
-a --age      set the age
-s --sex      set the sex
-m --metric   Use metric values
-i --imperial Use Imperial/USA values
-b --bodyfat  Used for the optional Katch-McArdle/Cunningham research methods
--male        set the sex to male
--female      set the sex to female
""")
        exit()

    weight = None
    height = None
    age    = None
    sex    = None
    metric = None
    bf     = None

    index = 1
    while index < len(argv):
        if   argv[index] == '-w':
            weight = float(argv[index+1])
            index += 1
        elif argv[index] == '--weight':
            weight = float(argv[index+1])
            index += 1
        elif argv[index] == '-h':
            height = float(argv[index+1])
            index += 1
        elif argv[index] == '--height':
            height = float(argv[index+1])
            index += 1
        elif argv[index] == '-a':
            age = float(argv[index+1])
            index += 1
        elif argv[index] == '--age':
            age = float(argv[index+1])
            index += 1
        elif argv[index] == '-s':
            sex = str(argv[index+1])
            index += 1
        elif argv[index] == '--sex':
            sex = float(argv[index+1])
            index += 1
        elif argv[index] == '--male':
            sex = 'M'
        elif argv[index] == '--female':
            sex = 'F'
        elif argv[index] == '-m':
            metric = 1
        elif argv[index] == '--metric':
            metric = 1
        elif argv[index] == '-i':
            metric = 0
        elif argv[index] == '--imperial':
            metric = 0
        elif argv[index] == '-b':
            bf = float(argv[index+1])
            index += 1
        elif argv[index] == '--bodyfat':
            bf = float(argv[index+1])
            index += 1
        index+= 1
    main(metric,sex,weight,height,age,bf)