activity_level = [None, 1.2, 1.375, 1.55, 1.725, 1.9]
...

if gender == 'male':
    bmr = (66 + (6.3*int(weight)) + (12.9*int(height)) - (6.8*int(age)))
    calorie = bmr * ativity_levels[activity_level]
...