initialising a list of lists

Cyril Bazin cyril.bazin at info.unicaen.fr
Wed Nov 16 14:51:06 CET 2005


Hello,

>>> b = [[] for _ in xrange(6)] # <- note the xrange!
>>> b[3].append('X')
>>> b
[[], [], [], ['X'], [], []]

This syntax might be less hairy but could be better when you use large
table.

You can hide this syntax by making a function:

def buildMatrix(nbRows):
return [[] for _ in xrange(nbRows)]

Then you call:

>>> b = buildMatrix(6)

Or:

>>> b = buildMatrix(nbRows=6)

Is it better for you?

Cyril


On 11/16/05, Peter Kleiweg <p.c.j.kleiweg at rug.nl> wrote:
>
> Fredrik Lundh schreef op de 16e dag van de slachtmaand van het jaar 2005:
>
> > Peter Kleiweg wrote:
> >
> > > This does not what I want it to do:
> > >
> > > >>> a = [[]] * 6
> > > >>> a[3].append('X')
> > > >>> a
> > > [['X'], ['X'], ['X'], ['X'], ['X'], ['X']]
> > >
> > > This does what I want:
> > >
> > > >>> b = [[] for _ in range(6)]
> > > >>> b[3].append('X')
> > > >>> b
> > > [[], [], [], ['X'], [], []]
> > >
> > > The first is clear and wrong. The second is hairy and right.
> > > Is there a way to do it clear and right?
> >
> >
> http://www.python.org/doc/faq/programming.html#how-do-i-create-a-multidimensional-list
>
> In other words: no there isn't.
>
> --
> Peter Kleiweg L:NL,af,da,de,en,ia,nds,no,sv,(fr,it) S:NL,de,en,(da,ia)
> info: http://www.let.rug.nl/~kleiweg/ls.html
> --
> http://mail.python.org/mailman/listinfo/python-list
>
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