def dec2bin(dec_nr):

    wynik = ''
    while dec_nr > 0:
        mod_r = dec_nr % 2
        dec_nr = dec_nr // 2

        wynik = str(mod_r) + wynik

    print(wynik)

dec2bin(41)
# "101001" = 41

def bin2dec(bin_nr):
    dec = 0
    i = 0
    while bin_nr > 0:
        mod_nr = bin_nr % 10
        bin_nr = bin_nr // 10 # 10100

        dec += mod_nr * (2 ** i)

        i += 1

    print(dec)
    
    # "10101"

def bin2dec_sposob2(bin_nr):
    dec_result = 0
    for n, i in enumerate(bin_nr[::-1]):
        dec_result += int(i) * (2 ** n)

    print(dec_result)

bin2dec(101001)
bin2dec_sposob2("00101001")