On 2010-01-27 21:06:28 -0500, Rotwang <sg...@hotmail.co.uk> said:
Hi all, I've been trying to make a class with which to manipulate sound
data, and have run into some behaviour I don't understand which I hope
somebody here can explain. The class has an attribute called data,
which is a list with two elements, one for each audio channel, each of
which is a list containing the audio data for that channel. It also has
various methods to write data such as sine waves and so on, and a
method to insert data from one sound at the start of data from another.
Schematically, the relevant bits look like this:
class sound:
def f(self):
self.data = [[0]]*2
Consider that this is equivalent to
def f(self):
x = [0]
self.data = [x, x]
self.data is now a list containing two references to the list
referenced by x -- so changes via either of the elements of self.data
will affect both elements. Your comprehension version creates a list
containing two distinct list objects, so this doesn't happen.
Can anybody tell me what's going on?
-o
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