Restricting user input to 64 bits?

Question

new to Python and i'm just wondering how to restrict the user input to make sure that they enter 64 bits

at the moment i've got this code

while True:
num = input('Please enter 64-bits')
if len(num=4)
    print ('Accepted')
    break
else:
    print ('Not Accepted, try again')

i know that line 3 is wrong but I'm pretty sure I have to use len in some way, any help is greatly appreciated, thanks!

Answer 1

The answer from falsetru won't work if the number starts with leading zeroes and you want to accept this as valid input.

You may want to use raw_input instead of input -- this way you'll get the raw string that the user enters. Then you can easily test the length of that string, in addition to converting the number with int(<x>, 2). Something like this, for instance:

while True:
    raw = raw_input('Please enter 64 bits: ')
    try:
        num = int(raw,2)
    except ValueError:
        print("Not a valid binary number")
        continue
    if len(raw)==64:
        print ('Accepted')
        break
    else:
        print ('Not Accepted, need exactly 64 bits.  Try again')

Answer 2

How about using int.bit_length method? (if you mean num is integer number)

>>> (1).bit_length()
1
>>> (2 ** 10).bit_length()
11
>>> (1 << 63).bit_length()
64

---

UPDATE

First convert the input string into number using int (with 2 as base).

>>> int('000001', 2)
1
>>> int('000001', 2).bit_length()
1
>>> int('00101', 2)
5
>>> int('00101', 2).bit_length()
3