& is "bitwise and" operand in Python, you should use and instead

from wiki.python.org:

x & y : Does a "bitwise and". Each bit of the output is 1 if the corresponding bit of x AND of y is 1, otherwise it's 0.

"bitwise and" works like this:

>>> 1 & 0
0
>>> 0 & 0
0
>>> 1 & 1
1