Mark Engelberg wrote:
That reminds me of a similar gotcha I've unfortunately run into on
more than one occasion.
# intialize a to be a list of 5 empty lists
a = 5*[[]]
# push a value onto the first list.
a[0].append(1)
What's a?
The result actually makes sense, although I did guess it wrong. :>(
>>> a = b = [1,2,3]
>>> c = [a,b] # a list with two references to the same object
>>> id(c[0])
3626848
>>> id(c[1])
3626848
>>> c[0][0] = 5
>>> a
[5, 2, 3]
What is b?
Would you rather have Python do something different?
When taking shortcuts like a = 5*[[]], never trust, always verify.
-- Dave
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