On 1/18/2014 3:50 AM, Peter Otten wrote:
Unlike `&` `and` cannot be overridden (*),
(*) I assume overriding would collide with short-cutting of boolean
expressions.
Yes. 'and' could be called a 'control-flow operator', but in Python it
is not a functional operator.
A functional binary operator expression like 'a + b' abbreviates a
function call, without using (). In this case, it could be written
'operator.add(a,b)'. This function, or it internal equivalent, calls
either a.__add__(b) or b.__radd__(a) or both. It is the overloading of
the special methods that overrides the operator.
The control flow expression 'a and b' cannot abbreviate a function call
because Python calls always evaluate all arguments first. It is
equivalent* to the conditional (control flow) *expression* (also not a
function operator) 'a if not a else b'. Evaluation of either expression
calls bool(a) and hence a.__bool__ or a.__len__.
'a or b' is equivalent* to 'a if a else b'
* 'a (and/or) b' evaluates 'a' once, whereas 'a if (not/)a else b'
evaluates 'a' twice. This is not equivalent when there are side-effects.
Here is an example where this matters.
input('enter a non-0 number :') or 1
--
Terry Jan Reedy
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