Re: [Visualpython-users] bug incrementing vector ?

[Jonathan B. <jbr...@ea...>]

On Tue, 2004-08-17 at 15:11, gp...@ri... wrote:
>  Should I expect that "+=" will not increment a vector?

It should work (and does, as far as I can tell) partially because
visual.vector provides the __iadd__() "special member function".  Worst
case, event if a visual.vector only provided __add__(), the interpreter
would synthesize the expression "x += y" as "x = x + y".  Python floats
are manipulated in this way.

Consider this toy example:

>>> class fwrap(object):
...     def __init__(self):
...         self.x = 1.0
...     def get(self):
...         return self.x
...     def __add__(self, other):
...         return self.x + other
...
>>> f = fwrap()
>>> f.get()
1.0
>>> f + 1.0
2.0
>>> f += 1.0
>>> f.get()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
AttributeError: 'float' object has no attribute 'get'
>>> f
2.0

HTH,
-Jonathan