pole_i_obwod_prostokata.py

a = 0
b = 0

while (a <= 0 and b <= 0):
    try:
        a = float(input('Pierwszy bok [cm]: '))
        if a <= 0:
            raise ValueError
        b = float(input('Drugi bok [cm]: '))
        if a <= 0:
            raise ValueError
    except ValueError:
        a = 0
        b = 0
    else:
        break

print(f'Obwod prostokata: {2*a+2*b} [cm]\nPole prostokata {a*b} [cm]')