How to initialize a list to a certain value in Python

Question

I'd like to get a list where each item is set to a certain value (in my case, 0). I've solved this in my code with the code below, but it feels so messy. Surely there's a better way?

maxWidths = map(lambda x: 0, range(0, maxCols))

Petr Viktorin · Accepted Answer · 2012-01-15 15:46:45Z

7

Multiply a one-element list by the desired length.

maxWidths = [0] * maxCols

In the above, all elements of the list will be the same objects. In case you're be creating a list of mutable values (such as dicts or lists), and you need them to be distinct, you can either use map as you did in the question, or write an equivalent list comprehension:

[[] for dummy in range(100)]

edited Jan 15, 2012 at 15:46

answered Jan 15, 2012 at 15:39

Petr Viktorin

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4 Comments

nickf Over a year ago

I knew there'd be a "python" way! Thanks.

user395760 Over a year ago

@nickf Note that the resulting list has maxCols references to the same objects. With mutable objects, this leads to quite different (and almost never desriable) semantics.

Roman Susi Over a year ago

To further clarify/illustrate: [[]] * maxCols list will actually contain maxCols "references" to the same list.

Petr Viktorin Over a year ago

@delnan: I was just updating the answer with that. Good catch :)

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