The part that converts the binary is int. From the documentation:

if base is given, then x must be a string, bytes, or bytearray instance representing an integer literal in radix base.

This means that int accepts a string representing an integer, that you tell it the base of. E.g. here we give it "11", and tell it this is in base 2, so it returns the integer 3 in decimal.

>>> int("11", 2)
3

Note that when supplying the base argument, you have to give a string:

>>> int(11, 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: int() can't convert non-string with explicit base

And you can't use digits that are invalid in the given base:

>>> int("21", 2)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: invalid literal for int() with base 2: '21'

Just take your print() instruction out of your for loop, otherwise it will print every step to your answer.

You can use int and set the base to 2 (for binary):

>>> binary = raw_input('enter a number: ')
enter a number: 11001
>>> int(binary, 2)
25
>>>

However, if you cannot use int like that, then you could always do this:

binary = raw_input('enter a number: ')
decimal = 0
for digit in binary:
    decimal = decimal*2 + int(digit)
print decimal

Below is a demonstration:

>>> binary = raw_input('enter a number: ')
enter a number: 11001
>>> decimal = 0
>>> for digit in binary:
...     decimal = decimal*2 + int(digit)
...
>>> print decimal
25
>>>

You do have to print the value:

>>> print(bin(160))  # This version gives the 0b prefix for binary numbers.
0b10100000
>>> print(format(160,'08b'))  # This specifies leading 0, 8 digits, binary.
10100000
>>> print('{:08b}'.format(160)) # Another way to format.
10100000
>>> print(f'{160:08b}')  # Python 3.6+ new f-string format.
10100000

The example given has nine bits, not eight: a "1" and eight "0"s.

First you must know what form of binary number it is, as there are several conventions, such as unsigned, signed, binary coded decimal, etc.

Assuming that this is a simple, unsigned binary number, the nine bits have the following values: 256, 128, 64, 32, 16, 8, 4, 2, and 1. To find the value in decimal, add up all the values that have a "1" in that position. In this case, the number in decimal is simply 256.

Another example might be: 010001001 In this case, you add 128, 8, and 1, to get 137. This can also be represented by an eight-bit number: 10001001

If, on the other hand, this is a signed number, it's more complicated. For a signed nine-bit number (which is not often encountered), the ninth bit on the left says whether it's negative or positive, with a "1" indicating negative. In the "twos complement" form, the remaining bits are inverted and then 1 is added. In this case, 00000000 is inverted to 11111111, then 1 is added, making it 100000000, or 256. Thus the number is -256.