Simplifying function

[perfringo]

There are several options pending of datatype of input and expected datatype of output

There is built-in function int() which doesn't fall under 'using any extra modules'.

>>> int('101010', 2)      # input is string, output is integer
42

There is also f-string in 3.6 <= Python which can be used for conversion:

>>> f'{0b101010:#0}'      # input is binary, output is string
'42'

bi_to_dec function can be rewritten to avoid conversion into str by using built-in divmod():

def binary_to_int(binary):
    integer = 0
    power = 0
    while binary:
        binary, reminder = divmod(binary, 10)
        integer += reminder*2**power
        power += 1
    return integer

Note about bi_to_dec - I recommend not to return print. Return value and let programmer decide whether it is necessary display this value or use it in expressions/statements.