Roy Smith wrote:
In article <4b0a01a...@dnews.tpgi.com.au>, Lie Ryan <lie.1...@gmail.com>
wrote:
The semantic of the in-place operator is something like:
x += y
becomes
x = x.__iadd__(y)
Except that the expression x is evaluated just once instead of twice.
thus
foo.bar += baz
becomes
foo.bar = foo.bar.__iadd__(baz)
So the call sequence is,
foo.__getattr__('bar') ==> x
x.__iadd__(baz) ==> y
foo.__setattr__('bar', y)
I don't get where the __setattr__() call comes from in this situation.
Augmented *ASSIGNMENT* is a type of assignment.
The dis module can be used to see what CPython does.
>>> from dis import dis
>>> def f():
foo.bar += baz
>>> dis(f)
2 0 LOAD_GLOBAL 0 (foo)
3 DUP_TOP
4 LOAD_ATTR 1 (bar)
7 LOAD_GLOBAL 2 (baz)
10 INPLACE_ADD
11 ROT_TWO
12 STORE_ATTR 1 (bar)
...
This amounts to what Roy said, with x and y being temporary entries on
the stack.
Terry Jan Reedy
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