Logical vs. bitwise operator AND
Question:
I don’t understand the difference between & and and, even if I read some other questions about it.
My code is:
f=1
x=1
f==1 & x==1
Out[60]: True
f==1 and x==1
Out[61]: True
f=1
x=2
f==1 and x==2
Out[64]: True
f==1 & x==2
Out[65]: False
Why is it the second & False, whereas the first is True?
Answers:
The issue is that & has higher operator precedence than ==.
>>> (f == 1) & (x == 2)
True
>>> f == (1 & x) == 2
False
Perhaps this seems unintuitive, but & is really meant to be used between numbers for particular kinds of calculations:
>>> 3 & 5
1
so it has similar precedence to operators like + and *, which sensibly should be evaluated before ==. It’s not meant to be used in a similar manner to and at all.
The problem is that ‘&’ has higher priority than ==. If you put your last statement like:
(f==1) & (x==2)
You will get your desired result.
In the second case, your code is:
f == (1 & x) == 2
1 & 2 is 0:
00000001
00000010 &
--------
00000000
So your final statement looks:
1 == 0 == 2
Which is False.
Logical AND (and) gives you an answer in true or false (boolean answer) whereas Bitwise AND (&) operator gives you an answer in digits after converting them to binary and applying a truth table on numbers.
I don’t understand the difference between & and and, even if I read some other questions about it.
My code is:
f=1
x=1
f==1 & x==1
Out[60]: True
f==1 and x==1
Out[61]: True
f=1
x=2
f==1 and x==2
Out[64]: True
f==1 & x==2
Out[65]: False
Why is it the second & False, whereas the first is True?
The issue is that & has higher operator precedence than ==.
>>> (f == 1) & (x == 2)
True
>>> f == (1 & x) == 2
False
Perhaps this seems unintuitive, but & is really meant to be used between numbers for particular kinds of calculations:
>>> 3 & 5
1
so it has similar precedence to operators like + and *, which sensibly should be evaluated before ==. It’s not meant to be used in a similar manner to and at all.
The problem is that ‘&’ has higher priority than ==. If you put your last statement like:
(f==1) & (x==2)
You will get your desired result.
In the second case, your code is:
f == (1 & x) == 2
1 & 2 is 0:
00000001
00000010 &
--------
00000000
So your final statement looks:
1 == 0 == 2
Which is False.
Logical AND (and) gives you an answer in true or false (boolean answer) whereas Bitwise AND (&) operator gives you an answer in digits after converting them to binary and applying a truth table on numbers.