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
>>>
```