bpo-29981: Add examples and update index for set, dict, and generator comprehensions'(GH-20272)
Co-authored-by: Rémi Lapeyre <remi.lapeyre@henki.fr>
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@ -308,6 +308,12 @@ Glossary
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keys can be any object with :meth:`__hash__` and :meth:`__eq__` methods.
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Called a hash in Perl.
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dictionary comprehension
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A compact way to process all or part of the elements in an iterable and
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return a dictionary with the results. ``results = {n: n ** 2 for n in
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range(10)}`` generates a dictionary containing key ``n`` mapped to
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value ``n ** 2``. See :ref:`comprehensions`.
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dictionary view
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The objects returned from :meth:`dict.keys`, :meth:`dict.values`, and
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:meth:`dict.items` are called dictionary views. They provide a dynamic
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@ -1026,6 +1032,12 @@ Glossary
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interface can be registered explicitly using
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:func:`~abc.register`.
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set comprehension
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A compact way to process all or part of the elements in an iterable and
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return a set with the results. ``results = {c for c in 'abracadabra' if
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c not in 'abc'}`` generates the set of strings ``{'r', 'd'}``. See
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:ref:`comprehensions`.
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single dispatch
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A form of :term:`generic function` dispatch where the implementation is
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chosen based on the type of a single argument.
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@ -4140,6 +4140,12 @@ The constructors for both classes work the same:
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objects. If *iterable* is not specified, a new empty set is
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returned.
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Sets can be created by several means:
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* Use a comma-separated list of elements within braces: ``{'jack', 'sjoerd'}``
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* Use a set comprehension: ``{c for c in 'abracadabra' if c not in 'abc'}``
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* Use the type constructor: ``set()``, ``set('foobar')``, ``set(['a', 'b', 'foo'])``
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Instances of :class:`set` and :class:`frozenset` provide the following
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operations:
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@ -4332,6 +4338,14 @@ pairs within braces, for example: ``{'jack': 4098, 'sjoerd': 4127}`` or ``{4098:
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Return a new dictionary initialized from an optional positional argument
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and a possibly empty set of keyword arguments.
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Dictionaries can be created by several means:
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* Use a comma-separated list of ``key: value`` pairs within braces:
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``{'jack': 4098, 'sjoerd': 4127}`` or ``{4098: 'jack', 4127: 'sjoerd'}``
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* Use a dict comprehension: ``{}``, ``{x: x ** 2 for x in range(10)}``
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* Use the type constructor: ``dict()``,
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``dict([('foo', 100), ('bar', 200)])``, ``dict(foo=100, bar=200)``
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If no positional argument is given, an empty dictionary is created.
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If a positional argument is given and it is a mapping object, a dictionary
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is created with the same key-value pairs as the mapping object. Otherwise,
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@ -162,6 +162,8 @@ ambiguities and allow common typos to pass uncaught.
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Displays for lists, sets and dictionaries
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-----------------------------------------
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.. index:: single: comprehensions
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For constructing a list, a set or a dictionary Python provides special syntax
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called "displays", each of them in two flavors:
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@ -260,6 +262,7 @@ Set displays
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.. index::
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pair: set; display
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pair: set; comprehensions
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object: set
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single: {} (curly brackets); set expression
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single: , (comma); expression list
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@ -287,6 +290,7 @@ Dictionary displays
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.. index::
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pair: dictionary; display
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pair: dictionary; comprehensions
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key, datum, key/datum pair
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object: dictionary
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single: {} (curly brackets); dictionary expression
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