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Rewrap to 70-characters.

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Georg Brandl 2012-10-06 13:04:01 +02:00
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pep-0424.txt
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@ -14,9 +14,9 @@ Abstract
========
CPython currently defines a ``__length_hint__`` method on several
types, such as various iterators. This method is then used by various
types, such as various iterators. This method is then used by various
other functions (such as ``list``) to presize lists based on the
estimate returned by ``__length_hint__``. Types which are not sized,
estimate returned by ``__length_hint__``. Types which are not sized,
and thus should not define ``__len__``, can then define
``__length_hint__``, to allow estimating or computing a size (such as
many iterators).
@ -24,18 +24,19 @@ many iterators).
Specification
=============
This PEP formally documents ``__length_hint__`` for other
interpreters and non-standard-library Python modules to implement.
This PEP formally documents ``__length_hint__`` for other interpreters
and non-standard-library Python modules to implement.
``__length_hint__`` must return an integer (else a ``TypeError`` is raised) or
``NotImplemented``, and is not required to be accurate. It may return a value
that is either larger or smaller than the actual size of the container. A
return value of ``NotImplemented`` indicates that there is no finite length
estimate. It may not return a negative value (else a ValueError is raised).
``__length_hint__`` must return an integer (else a ``TypeError`` is
raised) or ``NotImplemented``, and is not required to be accurate. It
may return a value that is either larger or smaller than the actual
size of the container. A return value of ``NotImplemented`` indicates
that there is no finite length estimate. It may not return a negative
value (else a ValueError is raised).
In addition, a new function ``operator.length_hint`` hint is added,
with the following semantics (which define how ``__length_hint__`` should
be used)::
with the following semantics (which define how ``__length_hint__``
should be used)::
def length_hint(obj, default=0):
"""Return an estimate of the number of items in obj.
@ -71,10 +72,10 @@ be used)::
Rationale
=========
Being able to pre-allocate lists based on the expected size, as estimated by
``__length_hint__``, can be a significant optimization. CPython has been
observed to run some code faster than PyPy, purely because of this optimization
being present.
Being able to pre-allocate lists based on the expected size, as
estimated by ``__length_hint__``, can be a significant optimization.
CPython has been observed to run some code faster than PyPy, purely
because of this optimization being present.
Copyright
=========