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authorGeorg Brandl <georg@python.org>2010-10-06 08:03:21 (GMT)
committerGeorg Brandl <georg@python.org>2010-10-06 08:03:21 (GMT)
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downloadcpython-16489247aae58e6cfdc8f76fa02867a5e624063d.zip
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Merged revisions 79901,80170,80273,80342-80343,81061,81366,81368,81370,81840 via svnmerge from
svn+ssh://svn.python.org/python/branches/py3k ................ r79901 | georg.brandl | 2010-04-08 08:33:16 +0200 (Do, 08 Apr 2010) | 1 line Fix indentation. ................ r80170 | georg.brandl | 2010-04-18 11:50:07 +0200 (So, 18 Apr 2010) | 1 line Remove colspanning cells. ................ r80273 | georg.brandl | 2010-04-20 20:15:54 +0200 (Di, 20 Apr 2010) | 1 line Markup nit. ................ r80342 | georg.brandl | 2010-04-22 09:00:42 +0200 (Do, 22 Apr 2010) | 1 line Fix indentation. ................ r80343 | georg.brandl | 2010-04-22 09:02:51 +0200 (Do, 22 Apr 2010) | 1 line Typo fixes. ................ r81061 | georg.brandl | 2010-05-10 23:17:00 +0200 (Mo, 10 Mai 2010) | 1 line Fix nits in the lexical analysis section: \u requires four digits, backtick is not allowed in source in 3.x. ................ r81366 | georg.brandl | 2010-05-19 22:58:02 +0200 (Mi, 19 Mai 2010) | 61 lines Recorded merge of revisions 80030,80067,80069,80080-80081,80084,80432-80433,80465,80470,81059,81065-81067 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r80030 | georg.brandl | 2010-04-13 08:43:54 +0200 (Di, 13 Apr 2010) | 1 line Get rid of multi-row cells. ........ r80067 | georg.brandl | 2010-04-14 10:53:38 +0200 (Mi, 14 Apr 2010) | 1 line #5341: typo. ........ r80069 | georg.brandl | 2010-04-14 15:50:31 +0200 (Mi, 14 Apr 2010) | 1 line Add an x-ref to where the O_ constants are documented and move the SEEK_ constants after lseek(). ........ r80080 | georg.brandl | 2010-04-14 21:16:38 +0200 (Mi, 14 Apr 2010) | 1 line #8399: add note about Windows and O_BINARY. ........ r80081 | georg.brandl | 2010-04-14 23:34:44 +0200 (Mi, 14 Apr 2010) | 1 line #5250: document __instancecheck__ and __subclasscheck__. I hope the part about the class/metaclass distinction is understandable. ........ r80084 | georg.brandl | 2010-04-14 23:46:45 +0200 (Mi, 14 Apr 2010) | 1 line Fix missing. ........ r80432 | georg.brandl | 2010-04-24 10:56:58 +0200 (Sa, 24 Apr 2010) | 1 line Markup fixes. ........ r80433 | georg.brandl | 2010-04-24 11:08:10 +0200 (Sa, 24 Apr 2010) | 1 line #7507: quote "!" in pipes.quote(); it is a special character for some shells. ........ r80465 | georg.brandl | 2010-04-25 12:29:17 +0200 (So, 25 Apr 2010) | 1 line Remove LaTeXy index entry syntax. ........ r80470 | georg.brandl | 2010-04-25 12:57:15 +0200 (So, 25 Apr 2010) | 1 line Patch from Tim Hatch: Make socket setblocking <-> settimeout examples symmetric. ........ r81059 | georg.brandl | 2010-05-10 23:02:51 +0200 (Mo, 10 Mai 2010) | 1 line #8642: fix wrong function name. ........ r81065 | georg.brandl | 2010-05-10 23:46:50 +0200 (Mo, 10 Mai 2010) | 1 line Fix reference direction. ........ r81066 | georg.brandl | 2010-05-10 23:50:57 +0200 (Mo, 10 Mai 2010) | 1 line Consolidate deprecation messages. ........ r81067 | georg.brandl | 2010-05-10 23:51:33 +0200 (Mo, 10 Mai 2010) | 1 line Fix typo. ........ ................ r81368 | georg.brandl | 2010-05-19 23:06:36 +0200 (Mi, 19 Mai 2010) | 9 lines Merged revisions 80068 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r80068 | georg.brandl | 2010-04-14 10:56:01 +0200 (Mi, 14 Apr 2010) | 1 line #5341: fix typo and adapt docstring syntax. ........ ................ r81370 | georg.brandl | 2010-05-19 23:39:51 +0200 (Mi, 19 Mai 2010) | 1 line Add descriptor HOWTO to py3k docs. ................ r81840 | alexander.belopolsky | 2010-06-08 20:59:20 +0200 (Di, 08 Jun 2010) | 9 lines Merged revisions 81489 via svnmerge from svn+ssh://pythondev@svn.python.org/python/trunk ........ r81489 | georg.brandl | 2010-05-23 17:29:29 -0400 (Sun, 23 May 2010) | 1 line #1436346: make it more obvious that timetuple[7] is yday. ........ ................
Diffstat (limited to 'Doc')
-rw-r--r--Doc/howto/descriptor.rst431
-rw-r--r--Doc/howto/index.rst1
-rw-r--r--Doc/library/datetime.rst17
-rw-r--r--Doc/library/multiprocessing.rst10
-rw-r--r--Doc/library/urllib.request.rst2
-rw-r--r--Doc/reference/lexical_analysis.rst8
6 files changed, 452 insertions, 17 deletions
diff --git a/Doc/howto/descriptor.rst b/Doc/howto/descriptor.rst
new file mode 100644
index 0000000..a9ef1d8
--- /dev/null
+++ b/Doc/howto/descriptor.rst
@@ -0,0 +1,431 @@
+======================
+Descriptor HowTo Guide
+======================
+
+:Author: Raymond Hettinger
+:Contact: <python at rcn dot com>
+
+.. Contents::
+
+Abstract
+--------
+
+Defines descriptors, summarizes the protocol, and shows how descriptors are
+called. Examines a custom descriptor and several built-in python descriptors
+including functions, properties, static methods, and class methods. Shows how
+each works by giving a pure Python equivalent and a sample application.
+
+Learning about descriptors not only provides access to a larger toolset, it
+creates a deeper understanding of how Python works and an appreciation for the
+elegance of its design.
+
+
+Definition and Introduction
+---------------------------
+
+In general, a descriptor is an object attribute with "binding behavior", one
+whose attribute access has been overridden by methods in the descriptor
+protocol. Those methods are :meth:`__get__`, :meth:`__set__`, and
+:meth:`__delete__`. If any of those methods are defined for an object, it is
+said to be a descriptor.
+
+The default behavior for attribute access is to get, set, or delete the
+attribute from an object's dictionary. For instance, ``a.x`` has a lookup chain
+starting with ``a.__dict__['x']``, then ``type(a).__dict__['x']``, and
+continuing through the base classes of ``type(a)`` excluding metaclasses. If the
+looked-up value is an object defining one of the descriptor methods, then Python
+may override the default behavior and invoke the descriptor method instead.
+Where this occurs in the precedence chain depends on which descriptor methods
+were defined. Note that descriptors are only invoked for new style objects or
+classes (a class is new style if it inherits from :class:`object` or
+:class:`type`).
+
+Descriptors are a powerful, general purpose protocol. They are the mechanism
+behind properties, methods, static methods, class methods, and :func:`super()`.
+They are used used throughout Python itself to implement the new style classes
+introduced in version 2.2. Descriptors simplify the underlying C-code and offer
+a flexible set of new tools for everyday Python programs.
+
+
+Descriptor Protocol
+-------------------
+
+``descr.__get__(self, obj, type=None) --> value``
+
+``descr.__set__(self, obj, value) --> None``
+
+``descr.__delete__(self, obj) --> None``
+
+That is all there is to it. Define any of these methods and an object is
+considered a descriptor and can override default behavior upon being looked up
+as an attribute.
+
+If an object defines both :meth:`__get__` and :meth:`__set__`, it is considered
+a data descriptor. Descriptors that only define :meth:`__get__` are called
+non-data descriptors (they are typically used for methods but other uses are
+possible).
+
+Data and non-data descriptors differ in how overrides are calculated with
+respect to entries in an instance's dictionary. If an instance's dictionary
+has an entry with the same name as a data descriptor, the data descriptor
+takes precedence. If an instance's dictionary has an entry with the same
+name as a non-data descriptor, the dictionary entry takes precedence.
+
+To make a read-only data descriptor, define both :meth:`__get__` and
+:meth:`__set__` with the :meth:`__set__` raising an :exc:`AttributeError` when
+called. Defining the :meth:`__set__` method with an exception raising
+placeholder is enough to make it a data descriptor.
+
+
+Invoking Descriptors
+--------------------
+
+A descriptor can be called directly by its method name. For example,
+``d.__get__(obj)``.
+
+Alternatively, it is more common for a descriptor to be invoked automatically
+upon attribute access. For example, ``obj.d`` looks up ``d`` in the dictionary
+of ``obj``. If ``d`` defines the method :meth:`__get__`, then ``d.__get__(obj)``
+is invoked according to the precedence rules listed below.
+
+The details of invocation depend on whether ``obj`` is an object or a class.
+Either way, descriptors only work for new style objects and classes. A class is
+new style if it is a subclass of :class:`object`.
+
+For objects, the machinery is in :meth:`object.__getattribute__` which
+transforms ``b.x`` into ``type(b).__dict__['x'].__get__(b, type(b))``. The
+implementation works through a precedence chain that gives data descriptors
+priority over instance variables, instance variables priority over non-data
+descriptors, and assigns lowest priority to :meth:`__getattr__` if provided. The
+full C implementation can be found in :cfunc:`PyObject_GenericGetAttr()` in
+`Objects/object.c <http://svn.python.org/view/python/trunk/Objects/object.c?view=markup>`_\.
+
+For classes, the machinery is in :meth:`type.__getattribute__` which transforms
+``B.x`` into ``B.__dict__['x'].__get__(None, B)``. In pure Python, it looks
+like::
+
+ def __getattribute__(self, key):
+ "Emulate type_getattro() in Objects/typeobject.c"
+ v = object.__getattribute__(self, key)
+ if hasattr(v, '__get__'):
+ return v.__get__(None, self)
+ return v
+
+The important points to remember are:
+
+* descriptors are invoked by the :meth:`__getattribute__` method
+* overriding :meth:`__getattribute__` prevents automatic descriptor calls
+* :meth:`__getattribute__` is only available with new style classes and objects
+* :meth:`object.__getattribute__` and :meth:`type.__getattribute__` make
+ different calls to :meth:`__get__`.
+* data descriptors always override instance dictionaries.
+* non-data descriptors may be overridden by instance dictionaries.
+
+The object returned by ``super()`` also has a custom :meth:`__getattribute__`
+method for invoking descriptors. The call ``super(B, obj).m()`` searches
+``obj.__class__.__mro__`` for the base class ``A`` immediately following ``B``
+and then returns ``A.__dict__['m'].__get__(obj, A)``. If not a descriptor,
+``m`` is returned unchanged. If not in the dictionary, ``m`` reverts to a
+search using :meth:`object.__getattribute__`.
+
+Note, in Python 2.2, ``super(B, obj).m()`` would only invoke :meth:`__get__` if
+``m`` was a data descriptor. In Python 2.3, non-data descriptors also get
+invoked unless an old-style class is involved. The implementation details are
+in :cfunc:`super_getattro()` in
+`Objects/typeobject.c <http://svn.python.org/view/python/trunk/Objects/typeobject.c?view=markup>`_
+and a pure Python equivalent can be found in `Guido's Tutorial`_.
+
+.. _`Guido's Tutorial`: http://www.python.org/2.2.3/descrintro.html#cooperation
+
+The details above show that the mechanism for descriptors is embedded in the
+:meth:`__getattribute__()` methods for :class:`object`, :class:`type`, and
+:func:`super`. Classes inherit this machinery when they derive from
+:class:`object` or if they have a meta-class providing similar functionality.
+Likewise, classes can turn-off descriptor invocation by overriding
+:meth:`__getattribute__()`.
+
+
+Descriptor Example
+------------------
+
+The following code creates a class whose objects are data descriptors which
+print a message for each get or set. Overriding :meth:`__getattribute__` is
+alternate approach that could do this for every attribute. However, this
+descriptor is useful for monitoring just a few chosen attributes::
+
+ class RevealAccess(object):
+ """A data descriptor that sets and returns values
+ normally and prints a message logging their access.
+ """
+
+ def __init__(self, initval=None, name='var'):
+ self.val = initval
+ self.name = name
+
+ def __get__(self, obj, objtype):
+ print('Retrieving', self.name)
+ return self.val
+
+ def __set__(self, obj, val):
+ print('Updating', self.name)
+ self.val = val
+
+ >>> class MyClass(object):
+ x = RevealAccess(10, 'var "x"')
+ y = 5
+
+ >>> m = MyClass()
+ >>> m.x
+ Retrieving var "x"
+ 10
+ >>> m.x = 20
+ Updating var "x"
+ >>> m.x
+ Retrieving var "x"
+ 20
+ >>> m.y
+ 5
+
+The protocol is simple and offers exciting possibilities. Several use cases are
+so common that they have been packaged into individual function calls.
+Properties, bound and unbound methods, static methods, and class methods are all
+based on the descriptor protocol.
+
+
+Properties
+----------
+
+Calling :func:`property` is a succinct way of building a data descriptor that
+triggers function calls upon access to an attribute. Its signature is::
+
+ property(fget=None, fset=None, fdel=None, doc=None) -> property attribute
+
+The documentation shows a typical use to define a managed attribute ``x``::
+
+ class C(object):
+ def getx(self): return self.__x
+ def setx(self, value): self.__x = value
+ def delx(self): del self.__x
+ x = property(getx, setx, delx, "I'm the 'x' property.")
+
+To see how :func:`property` is implemented in terms of the descriptor protocol,
+here is a pure Python equivalent::
+
+ class Property(object):
+ "Emulate PyProperty_Type() in Objects/descrobject.c"
+
+ def __init__(self, fget=None, fset=None, fdel=None, doc=None):
+ self.fget = fget
+ self.fset = fset
+ self.fdel = fdel
+ self.__doc__ = doc
+
+ def __get__(self, obj, objtype=None):
+ if obj is None:
+ return self
+ if self.fget is None:
+ raise AttributeError, "unreadable attribute"
+ return self.fget(obj)
+
+ def __set__(self, obj, value):
+ if self.fset is None:
+ raise AttributeError, "can't set attribute"
+ self.fset(obj, value)
+
+ def __delete__(self, obj):
+ if self.fdel is None:
+ raise AttributeError, "can't delete attribute"
+ self.fdel(obj)
+
+The :func:`property` builtin helps whenever a user interface has granted
+attribute access and then subsequent changes require the intervention of a
+method.
+
+For instance, a spreadsheet class may grant access to a cell value through
+``Cell('b10').value``. Subsequent improvements to the program require the cell
+to be recalculated on every access; however, the programmer does not want to
+affect existing client code accessing the attribute directly. The solution is
+to wrap access to the value attribute in a property data descriptor::
+
+ class Cell(object):
+ . . .
+ def getvalue(self, obj):
+ "Recalculate cell before returning value"
+ self.recalc()
+ return obj._value
+ value = property(getvalue)
+
+
+Functions and Methods
+---------------------
+
+Python's object oriented features are built upon a function based environment.
+Using non-data descriptors, the two are merged seamlessly.
+
+Class dictionaries store methods as functions. In a class definition, methods
+are written using :keyword:`def` and :keyword:`lambda`, the usual tools for
+creating functions. The only difference from regular functions is that the
+first argument is reserved for the object instance. By Python convention, the
+instance reference is called *self* but may be called *this* or any other
+variable name.
+
+To support method calls, functions include the :meth:`__get__` method for
+binding methods during attribute access. This means that all functions are
+non-data descriptors which return bound or unbound methods depending whether
+they are invoked from an object or a class. In pure python, it works like
+this::
+
+ class Function(object):
+ . . .
+ def __get__(self, obj, objtype=None):
+ "Simulate func_descr_get() in Objects/funcobject.c"
+ return types.MethodType(self, obj, objtype)
+
+Running the interpreter shows how the function descriptor works in practice::
+
+ >>> class D(object):
+ def f(self, x):
+ return x
+
+ >>> d = D()
+ >>> D.__dict__['f'] # Stored internally as a function
+ <function f at 0x00C45070>
+ >>> D.f # Get from a class becomes an unbound method
+ <unbound method D.f>
+ >>> d.f # Get from an instance becomes a bound method
+ <bound method D.f of <__main__.D object at 0x00B18C90>>
+
+The output suggests that bound and unbound methods are two different types.
+While they could have been implemented that way, the actual C implemention of
+:ctype:`PyMethod_Type` in
+`Objects/classobject.c <http://svn.python.org/view/python/trunk/Objects/classobject.c?view=markup>`_
+is a single object with two different representations depending on whether the
+:attr:`im_self` field is set or is *NULL* (the C equivalent of *None*).
+
+Likewise, the effects of calling a method object depend on the :attr:`im_self`
+field. If set (meaning bound), the original function (stored in the
+:attr:`im_func` field) is called as expected with the first argument set to the
+instance. If unbound, all of the arguments are passed unchanged to the original
+function. The actual C implementation of :func:`instancemethod_call()` is only
+slightly more complex in that it includes some type checking.
+
+
+Static Methods and Class Methods
+--------------------------------
+
+Non-data descriptors provide a simple mechanism for variations on the usual
+patterns of binding functions into methods.
+
+To recap, functions have a :meth:`__get__` method so that they can be converted
+to a method when accessed as attributes. The non-data descriptor transforms a
+``obj.f(*args)`` call into ``f(obj, *args)``. Calling ``klass.f(*args)``
+becomes ``f(*args)``.
+
+This chart summarizes the binding and its two most useful variants:
+
+ +-----------------+----------------------+------------------+
+ | Transformation | Called from an | Called from a |
+ | | Object | Class |
+ +=================+======================+==================+
+ | function | f(obj, \*args) | f(\*args) |
+ +-----------------+----------------------+------------------+
+ | staticmethod | f(\*args) | f(\*args) |
+ +-----------------+----------------------+------------------+
+ | classmethod | f(type(obj), \*args) | f(klass, \*args) |
+ +-----------------+----------------------+------------------+
+
+Static methods return the underlying function without changes. Calling either
+``c.f`` or ``C.f`` is the equivalent of a direct lookup into
+``object.__getattribute__(c, "f")`` or ``object.__getattribute__(C, "f")``. As a
+result, the function becomes identically accessible from either an object or a
+class.
+
+Good candidates for static methods are methods that do not reference the
+``self`` variable.
+
+For instance, a statistics package may include a container class for
+experimental data. The class provides normal methods for computing the average,
+mean, median, and other descriptive statistics that depend on the data. However,
+there may be useful functions which are conceptually related but do not depend
+on the data. For instance, ``erf(x)`` is handy conversion routine that comes up
+in statistical work but does not directly depend on a particular dataset.
+It can be called either from an object or the class: ``s.erf(1.5) --> .9332`` or
+``Sample.erf(1.5) --> .9332``.
+
+Since staticmethods return the underlying function with no changes, the example
+calls are unexciting::
+
+ >>> class E(object):
+ def f(x):
+ print(x)
+ f = staticmethod(f)
+
+ >>> print(E.f(3))
+ 3
+ >>> print(E().f(3))
+ 3
+
+Using the non-data descriptor protocol, a pure Python version of
+:func:`staticmethod` would look like this::
+
+ class StaticMethod(object):
+ "Emulate PyStaticMethod_Type() in Objects/funcobject.c"
+
+ def __init__(self, f):
+ self.f = f
+
+ def __get__(self, obj, objtype=None):
+ return self.f
+
+Unlike static methods, class methods prepend the class reference to the
+argument list before calling the function. This format is the same
+for whether the caller is an object or a class::
+
+ >>> class E(object):
+ def f(klass, x):
+ return klass.__name__, x
+ f = classmethod(f)
+
+ >>> print(E.f(3))
+ ('E', 3)
+ >>> print(E().f(3))
+ ('E', 3)
+
+
+This behavior is useful whenever the function only needs to have a class
+reference and does not care about any underlying data. One use for classmethods
+is to create alternate class constructors. In Python 2.3, the classmethod
+:func:`dict.fromkeys` creates a new dictionary from a list of keys. The pure
+Python equivalent is::
+
+ class Dict:
+ . . .
+ def fromkeys(klass, iterable, value=None):
+ "Emulate dict_fromkeys() in Objects/dictobject.c"
+ d = klass()
+ for key in iterable:
+ d[key] = value
+ return d
+ fromkeys = classmethod(fromkeys)
+
+Now a new dictionary of unique keys can be constructed like this::
+
+ >>> Dict.fromkeys('abracadabra')
+ {'a': None, 'r': None, 'b': None, 'c': None, 'd': None}
+
+Using the non-data descriptor protocol, a pure Python version of
+:func:`classmethod` would look like this::
+
+ class ClassMethod(object):
+ "Emulate PyClassMethod_Type() in Objects/funcobject.c"
+
+ def __init__(self, f):
+ self.f = f
+
+ def __get__(self, obj, klass=None):
+ if klass is None:
+ klass = type(obj)
+ def newfunc(*args):
+ return self.f(klass, *args)
+ return newfunc
+
diff --git a/Doc/howto/index.rst b/Doc/howto/index.rst
index 022beee..417ae00 100644
--- a/Doc/howto/index.rst
+++ b/Doc/howto/index.rst
@@ -16,6 +16,7 @@ Currently, the HOWTOs are:
advocacy.rst
cporting.rst
curses.rst
+ descriptor.rst
doanddont.rst
functional.rst
regex.rst
diff --git a/Doc/library/datetime.rst b/Doc/library/datetime.rst
index 5899ba7..456c1a0 100644
--- a/Doc/library/datetime.rst
+++ b/Doc/library/datetime.rst
@@ -455,7 +455,9 @@ Instance methods:
Return a :class:`time.struct_time` such as returned by :func:`time.localtime`.
The hours, minutes and seconds are 0, and the DST flag is -1. ``d.timetuple()``
is equivalent to ``time.struct_time((d.year, d.month, d.day, 0, 0, 0,
- d.weekday(), d.toordinal() - date(d.year, 1, 1).toordinal() + 1, -1))``
+ d.weekday(), yday, -1))``, where ``yday = d.toordinal() - date(d.year, 1,
+ 1).toordinal() + 1`` is the day number within the current year starting with
+ ``1`` for January 1st.
.. method:: date.toordinal()
@@ -919,12 +921,13 @@ Instance methods:
Return a :class:`time.struct_time` such as returned by :func:`time.localtime`.
``d.timetuple()`` is equivalent to ``time.struct_time((d.year, d.month, d.day,
- d.hour, d.minute, d.second, d.weekday(), d.toordinal() - date(d.year, 1,
- 1).toordinal() + 1, dst))`` The :attr:`tm_isdst` flag of the result is set
- according to the :meth:`dst` method: :attr:`tzinfo` is ``None`` or :meth:`dst`
- returns ``None``, :attr:`tm_isdst` is set to ``-1``; else if :meth:`dst`
- returns a non-zero value, :attr:`tm_isdst` is set to ``1``; else ``tm_isdst`` is
- set to ``0``.
+ d.hour, d.minute, d.second, d.weekday(), yday, dst))``, where ``yday =
+ d.toordinal() - date(d.year, 1, 1).toordinal() + 1`` is the day number within
+ the current year starting with ``1`` for January 1st. The :attr:`tm_isdst` flag
+ of the result is set according to the :meth:`dst` method: :attr:`tzinfo` is
+ ``None`` or :meth:`dst`` returns ``None``, :attr:`tm_isdst` is set to ``-1``;
+ else if :meth:`dst` returns a non-zero value, :attr:`tm_isdst` is set to ``1``;
+ else ``tm_isdst`` is set to ``0``.
.. method:: datetime.utctimetuple()
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 85a8241..7fbb258 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -61,15 +61,15 @@ object and then calling its :meth:`~Process.start` method. :class:`Process`
follows the API of :class:`threading.Thread`. A trivial example of a
multiprocess program is ::
- from multiprocessing import Process
+ from multiprocessing import Process
def f(name):
print('hello', name)
- if __name__ == '__main__':
- p = Process(target=f, args=('bob',))
- p.start()
- p.join()
+ if __name__ == '__main__':
+ p = Process(target=f, args=('bob',))
+ p.start()
+ p.join()
To show the individual process IDs involved, here is an expanded example::
diff --git a/Doc/library/urllib.request.rst b/Doc/library/urllib.request.rst
index c4a8a79..1278434 100644
--- a/Doc/library/urllib.request.rst
+++ b/Doc/library/urllib.request.rst
@@ -1058,7 +1058,7 @@ Examples
--------
This example gets the python.org main page and displays the first 300 bytes of
-it.::
+it. ::
>>> import urllib.request
>>> f = urllib.request.urlopen('http://www.python.org/')
diff --git a/Doc/reference/lexical_analysis.rst b/Doc/reference/lexical_analysis.rst
index aa30173..1b8b7b5 100644
--- a/Doc/reference/lexical_analysis.rst
+++ b/Doc/reference/lexical_analysis.rst
@@ -512,13 +512,13 @@ Notes:
(4)
Individual code units which form parts of a surrogate pair can be encoded using
- this escape sequence. Unlike in Standard C, exactly two hex digits are required.
+ this escape sequence. Exactly four hex digits are required.
(5)
Any Unicode character can be encoded this way, but characters outside the Basic
Multilingual Plane (BMP) will be encoded using a surrogate pair if Python is
- compiled to use 16-bit code units (the default). Individual code units which
- form parts of a surrogate pair can be encoded using this escape sequence.
+ compiled to use 16-bit code units (the default). Exactly eight hex digits
+ are required.
.. index:: unrecognized escape sequence
@@ -700,4 +700,4 @@ tokens or are otherwise significant to the lexical analyzer::
The following printing ASCII characters are not used in Python. Their
occurrence outside string literals and comments is an unconditional error::
- $ ?
+ $ ? `