|
Hi!
If I am missing a point here, what could it
be? Watch the hot spots (***)
Frederic #############################################################################
# Python 2.4, Windows ME
class Vertex (list):
def __init__ (self, *coordinates): self [:]
= list (coordinates [0:2])
def __add__ (self, V): return Vertex
(self [X] + V [X], self [Y] + V [Y])
def __iadd__ (self, V): self [X] += V [X];
self [Y] += V [Y]
>>> V1 = Vertex (1, 2)
>>> V2 = Vertex (4, 6) >>> V1 + V2
[5, 8] # OK >>> V1 +=
V2 # ***
V1 #
***
# *** died ? >>> print V1 None # *** V1 died ! >>> V2 [5, 8] # V2 is fine # Adding three traces to follow the state
of self
def __iadd__ (self,
V):
print 'A', self self [X] += V [X] print 'B', self self [Y] += V [Y] print 'C', self >>> V1 += V2
A [1, 2] B [5, 2] C [5, 8] # *** self is still OK when method terminates. # *** Also shows that operator += did call __iadd__, # *** (though the 2.4 doc no longer mentions it) # Explicit call works fine >>> V1.__iadd__ (V2)
A [1, 2] B [5, 2] C [5, 8] >>> V1
[5, 8] <<<< OK !!! |
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