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bpo-32306: Clarify c.f.Executor.map() documentation (#4947) 

The built-in map() function collects function arguments lazily, but concurrent.futures.Executor.map() does so eagerly.
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Antoine Pitrou 2017-12-20 19:06:20 +01:00 committed by GitHub
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Doc/library/concurrent.futures.rst
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@ -40,21 +40,29 @@ Executor Objects
.. method:: map(func, *iterables, timeout=None, chunksize=1)
Equivalent to :func:`map(func, *iterables) <map>` except *func* is executed
asynchronously and several calls to *func* may be made concurrently. The
returned iterator raises a :exc:`concurrent.futures.TimeoutError` if
:meth:`~iterator.__next__` is called and the result isn't available
Similar to :func:`map(func, *iterables) <map>` except:
* the *iterables* are collected immediately rather than lazily;
* *func* is executed asynchronously and several calls to
*func* may be made concurrently.
The returned iterator raises a :exc:`concurrent.futures.TimeoutError`
if :meth:`~iterator.__next__` is called and the result isn't available
after *timeout* seconds from the original call to :meth:`Executor.map`.
*timeout* can be an int or a float. If *timeout* is not specified or
``None``, there is no limit to the wait time. If a call raises an
exception, then that exception will be raised when its value is
retrieved from the iterator. When using :class:`ProcessPoolExecutor`, this
method chops *iterables* into a number of chunks which it submits to the
pool as separate tasks. The (approximate) size of these chunks can be
specified by setting *chunksize* to a positive integer. For very long
iterables, using a large value for *chunksize* can significantly improve
performance compared to the default size of 1. With :class:`ThreadPoolExecutor`,
*chunksize* has no effect.
``None``, there is no limit to the wait time.
If a *func* call raises an exception, then that exception will be
raised when its value is retrieved from the iterator.
When using :class:`ProcessPoolExecutor`, this method chops *iterables*
into a number of chunks which it submits to the pool as separate
tasks. The (approximate) size of these chunks can be specified by
setting *chunksize* to a positive integer. For very long iterables,
using a large value for *chunksize* can significantly improve
performance compared to the default size of 1. With
:class:`ThreadPoolExecutor`, *chunksize* has no effect.
.. versionchanged:: 3.5
Added the *chunksize* argument.