Q:

Why my reversing bits code written in Python gets this error?

I get this problem in Leetcode:
https://leetcode.com/problems/reverse-bits/
So the input will be a decimal integer and I have to turn it into binary 32 bits.
And then I reverse it and turn it back to decimal.
For example:
Input:
8 (whose binary == 1000)

Output:
1 (whose binary == 0001)

Here is my code:
# n is input number
str1 = str('{0:0{1}b}'.format(n,32))
len_str = len(str1)
index_swap = len_str - 1
result = [0] * len_str

for i, char in enumerate(str1):
    result[index_swap-i] = char

return int(str(''.join(result)),2)

If I run this code in Leetcode online Judge, I will get this error:
TypeError: sequence item 0: expected string, int found

This error is raised by the input 0.
I have no idea why it will raise this error. My code seems to works well!

A:

result = [0] * len_str

len_str is an int but a string was expected.
What should happen in that Line? Maybe:
result = [''  for x in xrange(len_str)]

which initialize an empty string of size len_str

