A ListComp that maintains its own state

[Bernhard Herzog]

Michael Spencer <mahs at telcopartners.com> writes:

> So, here's factorial in one line:
> # state refers to list of state history - it is initialized to [1]
> # on any iteration, the previous state is in state[-1]
> # the expression also uses the trick of list.append() => None
> # to both update the state, and return the last state
>
>  >>> [state.append(state[-1] * symbol) or state[-1]
> ...         for symbol, state in it.izip(range(1,10),it.repeat([1]))
> ...             ]
> [1, 2, 6, 24, 120, 720, 5040, 40320, 362880]
>  >>>

There's no need for repeat:

>>> [state.append(state[-1] * symbol) or state[-1] 
        for state in [[1]]
        for symbol in range(1, 10)]
[1, 2, 6, 24, 120, 720, 5040, 40320, 362880]


While we're at it, a while back I posted a list comprehension that
implements a 'recursive' flatten:

http://groups.google.de/groups?selm=s9zy8eyzcnl.fsf%40salmakis.intevation.de


   Bernhard

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