Please explain me what is the mask?

# I don't understand 13/14

**ionatan**#2

Bitmasks are used for manipulating specific bits of some data.

For example, if you want to read the 4th bit only, then you would create a mask with just the 4th bit turned on and use the bitwise AND operator:

```
fourth_bit = some_data & 0b1000
# fourth_bit will now be 0 or 8 depending on if that bit is on in `some_data`
```

**tsluyter**#4

While correct, your answer does not necessarily pertain to 13/14, where we are asked to bit-flip a whole byte. We're not looking for an &-operation to read one specific bit of a byte, we're flipping each 0->1 and 1->0. It's an XOR exercise.

To see a bit more on how XOR works compared to AND and OR, see my explanation here.

In the case of 13/14:

```
a = 0b11101110
print bin(a ^ 0b11111111)
```

Whose output is "0b10001", which is the simplified representation of "0b00010001".