0 
a = 2
b = 3
c = 4
x = y = z = [0 for i in xrange(a*b*c)]

Is there a way in which x,y,z can be initialized in one line (because I don't want to multiply a, b and c for each list initialization), as separate lists of 0s. In the above if x is updated, then y and z are also get updated simultaneously with the same changes.

Improve this question
1

2 Answers 2

Reset to default
3

Just use another comprehension and unpack it:

x, y, z = [[0 for i in xrange(a*b*c)] for _ in xrange(3)]

Note that [0 for i in xrange(a*b*c)] is equivalent to the simpler [0] * a*b*c.

Improve this answer
Sign up to request clarification or add additional context in comments.

7 Comments

how about using a generator so the list is not actually builded? a, b, c = ([0 for i in xrange(a*b*c)] for _ in xrange(3))
@DanielSanchez - We could do that, certainly. However, seeing any performance benefit from it would require creating many more lists than should be unpacked into multiple independent variables in a single line. It only has to store the references anyway, which are small.
please can you explain a bit further, as I see it you are building the a list wich contains another lists, but you will never use that list. By using a generator you just get rid of that list. Am I wrong or missing something? thanks!!
@DanielSanchez - It would get rid of a list, yes, but the list is tiny, and it should never be anything but tiny.
you meaned that, ok, either way I think it should not be used, just think it is in a loop of 1000 iterations, you will be creating 1000 lists, must take care of that. Thanks for the explanation, good answer.
|
1

Looking at your stated intention rather than at the 'one line' requirement:

a = 2
b = 3
c = 4
x = [0 for i in xrange(a*b*c)]
y = x [:]
z = x [:]

Not sure the optimizer is clever enough to avoid repeated multiplication at:

x, y, z = [[0 for i in xrange(a*b*c)] for _ in xrange(3)]

Suppose a, b, and c were properties, so reading them would have side effects. How could the optimizer know this in a dynamically typed language?

Improve this answer

Comments

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.