On Dec 6, 2019, at 16:44, Steven D'Aprano <[email protected]> wrote:
>
> We could, I guess, eliminate the difference by adding the ability to
> peek ahead to the next value of an arbitrary iterator without consuming
> that value. This would have to be done by the interpreter, not in Python
> code,
You can easily wrap an iterator to make it peekable. Untested, off the top of
my head on my phone:
class Peekable(Iterator):
_sentinel = object()
def __init__(self, it):
self._peek = self._sentinel
self._it = iter(it)
def __iter__(self):
return self
def __next__(self):
if self._peek is not self._sentinel:
result, self._peek = self._peek, self._sentinel
return result
return next(self._it)
def peek(self):
if self._peek is self._sentinel:
self._peek = next(self._it)
return self._peek
You can easily add a default value for peek, a prepend method, an isempty
method (or just call it __bool__), multiple levels of peek (use a deque, or
tee), combine the last two to prepend multiple values (which is equivalent to
chain, but sometimes more readable as a method), add indexing on top of the
multi-peek, …
There’s a version of this included in more-itertools, which I’ve used quite a
few times. I don’t remember exactly which extra features it comes with, because
usually I just want the basic peek.
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