Kaydet (Commit) 2654b86e authored tarafından Chris Jerdonek's avatar Chris Jerdonek

Link to "yield from" examples in yield documentation.

This commit also simplifies the more advanced "yield from" example and removes
unused function parameters.
üst 70dcef47
......@@ -320,7 +320,8 @@ Yield expressions
yield_atom: "(" `yield_expression` ")"
yield_expression: "yield" [`expression_list` | "from" `expression`]
The :keyword:`yield` expression is only used when defining a generator function,
The :keyword:`yield` expression is only used when defining a :term:`generator`
function,
and can only be used in the body of a function definition. Using a
:keyword:`yield` expression in a function definition is sufficient to cause that
definition to create a generator function instead of a normal function.
......@@ -438,6 +439,12 @@ is already executing raises a :exc:`ValueError` exception.
other exception, it is propagated to the caller. :meth:`close` does nothing
if the generator has already exited due to an exception or normal exit.
.. index:: single: yield; examples
Examples
^^^^^^^^
Here is a simple example that demonstrates the behavior of generators and
generator functions::
......@@ -465,6 +472,9 @@ generator functions::
>>> generator.close()
Don't forget to clean up when 'close()' is called.
For examples using ``yield from``, see :ref:`pep-380` in "What's New in
Python."
.. seealso::
......
......@@ -393,14 +393,18 @@ inspection of exception attributes::
PEP written and implemented by Antoine Pitrou
.. index::
single: yield; yield from (in What's New)
.. _pep-380:
PEP 380: Syntax for Delegating to a Subgenerator
================================================
PEP 380 adds the ``yield from`` expression, allowing a generator to delegate
PEP 380 adds the ``yield from`` expression, allowing a :term:`generator` to
delegate
part of its operations to another generator. This allows a section of code
containing 'yield' to be factored out and placed in another generator.
containing :keyword:`yield` to be factored out and placed in another generator.
Additionally, the subgenerator is allowed to return with a value, and the
value is made available to the delegating generator.
......@@ -421,15 +425,15 @@ However, unlike an ordinary loop, ``yield from`` allows subgenerators to
receive sent and thrown values directly from the calling scope, and
return a final value to the outer generator::
>>> def accumulate(start=0):
... tally = start
>>> def accumulate():
... tally = 0
... while 1:
... next = yield
... if next is None:
... return tally
... tally += next
...
>>> def gather_tallies(tallies, start=0):
>>> def gather_tallies(tallies):
... while 1:
... tally = yield from accumulate()
... tallies.append(tally)
......@@ -437,7 +441,7 @@ return a final value to the outer generator::
>>> tallies = []
>>> acc = gather_tallies(tallies)
>>> next(acc) # Ensure the accumulator is ready to accept values
>>> for i in range(10):
>>> for i in range(4):
... acc.send(i)
...
>>> acc.send(None) # Finish the first tally
......@@ -446,7 +450,7 @@ return a final value to the outer generator::
...
>>> acc.send(None) # Finish the second tally
>>> tallies
[45, 10]
[6, 10]
The main principle driving this change is to allow even generators that are
designed to be used with the ``send`` and ``throw`` methods to be split into
......
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