ugly script to calculate body fat percentage with uncertainties

calipo.py

#MIT License

# Copyright (c) 2020 Marius Engelhardt

# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
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# copies of the Software, and to permit persons to whom the Software is
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import uncertainties
from datetime import date
import numpy as np


def calculate_bfp(fatness: list, age: float, male=True) -> float:
    # Calculatebody fat percentage according to Jackson & Pollock https://doi.org/10.1079/BJN19780152
    if male:
        if len(fatness) == 3:  # 3 skinfold thicknesses
            k = [1.1093800, -0.0008267, 0.0000016, -0.0002574]  # k0 to k2 and k_a for age
            R = 0.905  # multiple correlation
            standard_error = 0.0077
        elif len(fatness) == 5:  # 3 skinfold thicknesses, 2 circumferences
            k = [1.0990750, -0.0008209, 0.0000026, -0.0002017, -0.005657,
                 0.018586]  # k0 to k2 and k_a for age, k4 for waist circumference, k5 for forearm circumference
            R = 0.918
            standard_error = 0.0072
        else:
            raise ValueError(f"No formula for fatness values of length {len(fatness)}")
    else:
        raise NotImplementedError("Measurements for women not implemented yet.")
    S = sum(fatness[:3])  # sum of skinfolds

    body_density = k[0] + k[1] * S + k[2] * S ** 2 + k[3] * age
    try:
        body_density += k[4] * fatness[3] * k[5] * fatness[4]
    except IndexError:
        pass

    body_density = uncertainties.ufloat(body_density, standard_error)
    print(f"Body density: {body_density}")

    # Brozek 1963
    bfp = (4.57 / body_density - 4.142) * 100
    print(f"BFP after Brozek: {bfp}")
    # Siri 1961
    bfp = (4.95 / body_density - 4.50) * 100
    print(f"BFP after Siri: {bfp}")

    return bfp


def calc_age(date_of_birth):
    dob = date.fromisoformat(date_of_birth)
    days_per_year = 365.24225  # according to https://pumas.nasa.gov/examples/index.php?id=46
    age = date.today() - dob
    return age.days / days_per_year


if __name__ == '__main__':
    # enter birthday here
    age = calc_age("1990-01-01")
    print(age)
    # enter skinfold thickness in mm into this list
    f = [8, 17, 15]
    f_u = [uncertainties.ufloat(v, 1) for v in f]
    calculate_bfp(f, age)
    calculate_bfp(f_u, age)