[Python-checkins] peps: Formatting fixes; use "::" shortcuts.
georg.brandl
python-checkins at python.org
Sun Oct 30 11:47:20 CET 2011
http://hg.python.org/peps/rev/8cfc3835e115
changeset: 3978:8cfc3835e115
user: Georg Brandl <georg at python.org>
date: Sun Oct 30 12:46:47 2011 +0100
summary:
Formatting fixes; use "::" shortcuts.
files:
pep-3152.txt | 95 ++++++++++++++++++---------------------
1 files changed, 44 insertions(+), 51 deletions(-)
diff --git a/pep-3152.txt b/pep-3152.txt
--- a/pep-3152.txt
+++ b/pep-3152.txt
@@ -14,16 +14,17 @@
Abstract
========
-A syntax is proposed for defining and calling a special type of generator
-called a 'cofunction'. It is designed to provide a streamlined way of
-writing generator-based coroutines, and allow the early detection of
-certain kinds of error that are easily made when writing such code, which
-otherwise tend to cause hard-to-diagnose symptoms.
+A syntax is proposed for defining and calling a special type of
+generator called a 'cofunction'. It is designed to provide a
+streamlined way of writing generator-based coroutines, and allow the
+early detection of certain kinds of error that are easily made when
+writing such code, which otherwise tend to cause hard-to-diagnose
+symptoms.
-This proposal builds on the 'yield from' mechanism described in PEP 380,
-and describes some of the semantics of cofunctions in terms of it. However,
-it would be possible to define and implement cofunctions independently of
-PEP 380 if so desired.
+This proposal builds on the 'yield from' mechanism described in PEP
+380, and describes some of the semantics of cofunctions in terms of
+it. However, it would be possible to define and implement cofunctions
+independently of PEP 380 if so desired.
Specification
@@ -32,29 +33,26 @@
Cofunction definitions
----------------------
-A new keyword ``codef`` is introduced which is used in place of ``def`` to
-define a cofunction. A cofunction is a special kind of generator having the
-following characteristics:
+A new keyword ``codef`` is introduced which is used in place of
+``def`` to define a cofunction. A cofunction is a special kind of
+generator having the following characteristics:
-1. A cofunction is always a generator, even if it does not contain any
+1. A cofunction is always a generator, even if it does not contain any
``yield`` or ``yield from`` expressions.
-2. A cofunction cannot be called the same way as an ordinary function. An
- exception is raised if an ordinary call to a cofunction is attempted.
+2. A cofunction cannot be called the same way as an ordinary function.
+ An exception is raised if an ordinary call to a cofunction is
+ attempted.
Cocalls
-------
Calls from one cofunction to another are made by marking the call with
-a new keyword ``cocall``. The expression
-
-::
+a new keyword ``cocall``. The expression ::
cocall f(*args, **kwds)
-is semantically equivalent to
-
-::
+is semantically equivalent to ::
yield from f.__cocall__(*args, **kwds)
@@ -62,48 +60,43 @@
iterator, so the step of calling iter() on it is skipped.
The full syntax of a cocall expression is described by the following
-grammar lines:
-
-::
+grammar lines::
atom: cocall | <existing alternatives for atom>
cocall: 'cocall' atom cotrailer* '(' [arglist] ')'
cotrailer: '[' subscriptlist ']' | '.' NAME
-The ``cocall`` keyword is syntactically valid only inside a cofunction.
-A SyntaxError will result if it is used in any other context.
+The ``cocall`` keyword is syntactically valid only inside a
+cofunction. A SyntaxError will result if it is used in any other
+context.
Objects which implement __cocall__ are expected to return an object
-obeying the iterator protocol. Cofunctions respond to __cocall__ the
+obeying the iterator protocol. Cofunctions respond to __cocall__ the
same way as ordinary generator functions respond to __call__, i.e. by
returning a generator-iterator.
-Certain objects that wrap other callable objects, notably bound methods,
-will be given __cocall__ implementations that delegate to the underlying
-object.
+Certain objects that wrap other callable objects, notably bound
+methods, will be given __cocall__ implementations that delegate to the
+underlying object.
New builtins, attributes and C API functions
--------------------------------------------
To facilitate interfacing cofunctions with non-coroutine code, there will
-be a built-in function ``costart`` whose definition is equivalent to
-
-::
+be a built-in function ``costart`` whose definition is equivalent to ::
def costart(obj, *args, **kwds):
return obj.__cocall__(*args, **kwds)
-There will also be a corresponding C API function
-
-::
+There will also be a corresponding C API function ::
PyObject *PyObject_CoCall(PyObject *obj, PyObject *args, PyObject *kwds)
It is left unspecified for now whether a cofunction is a distinct type
of object or, like a generator function, is simply a specially-marked
-function instance. If the latter, a read-only boolean attribute
-``__iscofunction__`` should be provided to allow testing whether a given
-function object is a cofunction.
+function instance. If the latter, a read-only boolean attribute
+``__iscofunction__`` should be provided to allow testing whether a
+given function object is a cofunction.
Motivation and Rationale
@@ -111,32 +104,32 @@
The ``yield from`` syntax is reasonably self-explanatory when used for
the purpose of delegating part of the work of a generator to another
-function. It can also be used to good effect in the implementation of
+function. It can also be used to good effect in the implementation of
generator-based coroutines, but it reads somewhat awkwardly when used
for that purpose, and tends to obscure the true intent of the code.
Furthermore, using generators as coroutines is somewhat error-prone.
-If one forgets to use ``yield from`` when it should have been used,
-or uses it when it shouldn't have, the symptoms that result can be
+If one forgets to use ``yield from`` when it should have been used, or
+uses it when it shouldn't have, the symptoms that result can be
obscure and confusing.
Finally, sometimes there is a need for a function to be a coroutine
even though it does not yield anything, and in these cases it is
-necessary to resort to kludges such as ``if 0: yield`` to force it
-to be a generator.
+necessary to resort to kludges such as ``if 0: yield`` to force it to
+be a generator.
The ``codef`` and ``cocall`` constructs address the first issue by
making the syntax directly reflect the intent, that is, that the
function forms part of a coroutine.
-The second issue is addressed
-by making it impossible to mix coroutine and non-coroutine code in
-ways that don't make sense. If the rules are violated, an exception
-is raised that points out exactly what and where the problem is.
+The second issue is addressed by making it impossible to mix coroutine
+and non-coroutine code in ways that don't make sense. If the rules
+are violated, an exception is raised that points out exactly what and
+where the problem is.
-Lastly, the need for dummy yields is eliminated by making the
-form of definition determine whether the function is a coroutine,
-rather than what it contains.
+Lastly, the need for dummy yields is eliminated by making the form of
+definition determine whether the function is a coroutine, rather than
+what it contains.
Prototype Implementation
--
Repository URL: http://hg.python.org/peps
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