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Why can't I use the '|' bitwise operator in this statement? (lemm.ee)
submitted 2 years ago* (last edited 2 years ago) by to c/python@programming.dev
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if coin == 25 | 10 | 5:

If I replace the '|' with 'or' the code runs just fine. I'm not sure why I can't use '|' in the same statement.

Doing the following doesn't work either:

if coin == 25 | coin == 10 | coin == 5:

I know bitwise operators can only be used with integers, but other then that is there another difference from logical operators?

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[–] 11 points 2 years ago* (last edited 2 years ago) (8 children)

But what is an example of where I can use it?

Aside from operations on bitfields, a bitwise operator can be useful in several "non bits" cases. For instance:

value & 1 evaluates to 1 if value is odd (and will evaluate to True in an if statement)
value >> 1 divides value by 2 (integer division)

But usually bitwise operators are for when you want to manipulate bits in values. For instance:

value | 5 returns value with bits 1 and 3 set to True
value & 0xffff returns the 16 least-significant bits in value (usually you do this to make sure it will fit in 2 bytes in memory for example)
value & (0xffff ^ 5) returns the lower 16 bits of value with bits 1 and 3 set to False

Etc.

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  • [–] [S] 7 points 2 years ago (7 children)

    Thank you for the reply. It seems bitwise operators are somewhat of an advanced concept that I may revisit down the road.

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  • [–] 9 points 2 years ago (3 children)

    honestly yes you're probably not going to use them a lot, if at all, especially in python

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  • [–] 6 points 2 years ago (2 children)

    You might use them with sets:

    a = {1, 2, 3}
b = {2, 3, 4}

a | b  # {1, 2, 3, 4}
a & b  # {2, 3}
a ^ b  # {1, 4}
a - b  # {1}
b - a  # {4}
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  • [–] 2 points 2 years ago (1 child)

    They're quite simple. Just convert the values to binary and apply the applicable truth tables. Just remember operator precedence when you use them, and in doubt, don't trust your luck and apply parentheses generously 🙂

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  • [–] 1 point 2 years ago*

    python in general tends toward readability over performance optimisation… you’re right they’re an advanced concept, and i’d say if you ever use bitwise operators in python they should be wrapped in some descriptive and very minimal function: treat it like a black box, because the next person that comes along likely won’t understand what’s happening without a pretty good description

    a bit field is just not a descriptive data structure, so manipulate it directly as little as possible

    i’d also say that most peoples use of bitwise operators is when unpacking external data formats (network traffic, operating system primitives, files formats, etc) and they’re usually wrapped in data structures that make those things more pythonic

    unless you know you need bitwise operators, you probably don’t need bitwise operators

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