Convert text to decimal python3 - python-3.x

Question

I need to convert words to numbers for RSA cipher, so i found code which can convert text to decimal, but when i run it in terminal by python 3 i get:
Traceback (most recent call last):
File "test.py", line 49, in <module>
numberOutput = int(bit_list_to_string(string_to_bits(inputString)),2) #1976620216402300889624482718775150
File "test.py", line 31, in string_to_bits
map(chr_to_bit, s)
File "test.py", line 30, in <listcomp>
return [b for group in
File "test.py", line 29, in chr_to_bit
return pad_bits(convert_to_bits(ord(c)), ASCII_BITS)
File "test.py", line 14, in pad_bits
assert len(bits) <= pad
AssertionError
when i use "python convert_text_to_decimal.py" in terminal it works correctly.
Code:
BITS = ('0', '1')
ASCII_BITS = 8
def bit_list_to_string(b):
"""converts list of {0, 1}* to string"""
return ''.join([BITS[e] for e in b])
def seq_to_bits(seq):
return [0 if b == '0' else 1 for b in seq]
def pad_bits(bits, pad):
"""pads seq with leading 0s up to length pad"""
assert len(bits) <= pad
return [0] * (pad - len(bits)) + bits
def convert_to_bits(n):
"""converts an integer `n` to bit array"""
result = []
if n == 0:
return [0]
while n > 0:
result = [(n % 2)] + result
n = n / 2
return result
def string_to_bits(s):
def chr_to_bit(c):
return pad_bits(convert_to_bits(ord(c)), ASCII_BITS)
return [b for group in
map(chr_to_bit, s)
for b in group]
def bits_to_char(b):
assert len(b) == ASCII_BITS
value = 0
for e in b:
value = (value * 2) + e
return chr(value)
def list_to_string(p):
return ''.join(p)
def bits_to_string(b):
return ''.join([bits_to_char(b[i:i + ASCII_BITS])
for i in range(0, len(b), ASCII_BITS)])
inputString = "attack at dawn"
numberOutput = int(bit_list_to_string(string_to_bits(inputString)),2) #1976620216402300889624482718775150
bitSeq = seq_to_bits(bin(numberOutput)[2:]) #[2:] is needed to get rid of 0b in front
paddedString = pad_bits(bitSeq,len(bitSeq) + (8 - (len(bitSeq) % 8))) #Need to pad because conversion from dec to bin throws away MSB's
outputString = bits_to_string(paddedString) #attack at dawn
So when i use just python he have 2.7 version. Please, help me fix this code to python 3

Answer 1

Change line 22,
n = n / 2
to
n = n // 2
This solves the immediate error you get (and another one that follows from it). The rest of the routine may or may not work for your purposes; I did not check any further.
You get the assert error because the function convert_to_bits should be, theoretically speaking, returning a proper list of single bit values for a valid integer in its range. It calculates this list by dividing the integer by 2 until 0 remains.
However.
One of the more significant changes from Python 2.7 to 3.x was the behavior of the division operator. Prior, this always returned an integer, but with Python 3 it was decided to have it return a float instead.
That means the simple bit calculation loop
while n > 0:
result = [(n % 2)] + result
n = n / 2
does not return a steady list of 0s and 1s anymore, always ending because the source integer runs out of numbers, but instead you get a list of more than a thousand floating point numbers. At a glance it may be unclear what that list represents, but as it ends with
… 1.03125, 0.0625, 0.125, 0.25, 0.5, 1]
you can see it's the divide-by-two loop that keeps on dividing until its input finally runs out of floating point accuracy and stops dividing further.
The resulting array is not only way, way larger than the next routines expect, its data is also of the wrong type. The values in this list are used as an index for the BITS tuple at the top of your code. With the floating point division, you get an error when trying to use the value as an index, even if it is a round 0.0 or 1.0. The integer division, again, fixes this.