Iteration, while loop, and for loop
steve at pearwood.info
Wed Jun 29 19:59:27 EDT 2016
On Thu, 30 Jun 2016 01:29 am, Ian Kelly wrote:
> On Tue, Jun 28, 2016 at 11:58 AM, Grant Edwards
> <grant.b.edwards at gmail.com> wrote:
>>> But then, if you wrap up your "while" loop as a generator that yields
>>> things, you can then use it in a "for" loop which seems to me like
>>> the Pythonic way to do things. :-)
>> Yea, I keep telling myself that, but I never actually do it.
> Here you go:
> import collections
> class MutableIterator:
[snip 8 methods and 33 lines of code]
> # Example:
>>>> mi = MutableIterator('bananas')
>>>> for char in mi:
> ... if char == 'a':
> ... mi.extend(' yum')
> ... print(char, end='')
> bananas yum yum yum
I'm curious what REPL you are using, because in the vanilla Python
interactive interpreter, the output if over-written by the prompt. That is,
what I see in Python 3.6 is:
py> nas yum yum yumpy>
unless I take steps to prevent that. See below.
But there's no need to go to such effort for a mutable iterator. This is
py> mi = list('bananas')
py> for char in mi:
... if char == 'a':
... mi.extend(' yum')
... print(char, end='')
... else: # oh no, the feared for...else!
... # needed to prevent the prompt overwriting the output
bananas yum yum yum
This example shows two things:
(1) There's no need for a MutableIterator, we have list;
(2) Anyone who says that for...else without break is useless is wrong.
“Cheer up,” they said, “things could be worse.” So I cheered up, and sure
enough, things got worse.
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