subtle side effect of generator/generator expression

bonono at gmail.com bonono at gmail.com
Sun Oct 16 17:41:48 CEST 2005


True. That is why I have now reverted back to use list whenever
possible. As while list can also be modified(say in a multi-thread
situation), at least if I don't do the update(coding policy, practice
or whatever), they are sort of "guaranteed".

I would only use generator as IO monad in Haskell, i.e. don't use it
unless I absolutely need to.

Diez B. Roggisch wrote:
>
> Its a question of protocol. A iterator only guarantes that you can fetch
> items from it until it is possibly exhausted. In the same way, a stream
> may only guarantee you that you can  read from it. If you need more, you
> have tgo use a different protocol. Lists are one that allows you to
> randomly access it. Files allow to seek, in addition to stream semantics.
>
> And given that python is an imperative language with side-effects, you
> don't know what sideeffects  a generator can cause - which makes a
> "rewind" or copy-semantics to make it work several time impossible (in
> the general case, that is). So it has to focus on what it _can_ guarantee.
>
> Haskell and other FP languages canwork differently here, as sideeffects
> are made excplicit using e.g. monads or other means - which allows for
> re-use of a generator-like construct. But there is no way to make this
> work in pythons paradigm.
> 
> Diez




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