bpo-28638: Optimize namedtuple() creation time by minimizing use of exec() (#3454)

* Working draft without _source

* Re-use itemgetter() instances

* Speed-up calls to __new__() with a pre-bound tuple.__new__()

* Add note regarding string interning

* Remove unnecessary create function wrappers

* Minor sync-ups with PR-2736.  Mostly formatting and f-strings

* Bring-in qualname/__module fix-ups from PR-2736

* Formally remove the verbose flag and _source attribute

* Restore a test of potentially problematic field names

* Restore kwonly_args test but without the verbose option

* Adopt Inada's idea to reuse the docstrings for the itemgetters

* Neaten-up a bit

* Add news blurb

* Serhiy pointed-out the need for interning

* Jelle noticed as missing f on an f-string

* Add whatsnew entry for feature removal

* Accede to request for dict literals instead keyword arguments

* Leave the method.__module__ attribute pointing the actual location of the code

* Improve variable names and add a micro-optimization for an non-public helper function

* Simplify by in-lining reuse_itemgetter()

* Arrange steps in more logical order

* Save docstring in local cache instead of interning

Author: rhettinger

Doc/library/collections.rst

@@ -763,7 +763,7 @@ Named tuples assign meaning to each position in a tuple and allow for more reada
 self-documenting code.  They can be used wherever regular tuples are used, and
 they add the ability to access fields by name instead of position index.
 
-.. function:: namedtuple(typename, field_names, *, verbose=False, rename=False, module=None)
+.. function:: namedtuple(typename, field_names, *, rename=False, module=None)
 
     Returns a new tuple subclass named *typename*.  The new subclass is used to
     create tuple-like objects that have fields accessible by attribute lookup as
@@ -786,10 +786,6 @@ they add the ability to access fields by name instead of position index.
     converted to ``['abc', '_1', 'ghi', '_3']``, eliminating the keyword
     ``def`` and the duplicate fieldname ``abc``.
 
-    If *verbose* is true, the class definition is printed after it is
-    built.  This option is outdated; instead, it is simpler to print the
-    :attr:`_source` attribute.
-
     If *module* is defined, the ``__module__`` attribute of the named tuple is
     set to that value.
 
@@ -806,6 +802,9 @@ they add the ability to access fields by name instead of position index.
     .. versionchanged:: 3.6
        Added the *module* parameter.
 
+    .. versionchanged:: 3.7
+       Remove the *verbose* parameter and the :attr:`_source` attribute.
+
 .. doctest::
     :options: +NORMALIZE_WHITESPACE
 
@@ -878,15 +877,6 @@ field names, the method and attribute names start with an underscore.
         >>> for partnum, record in inventory.items():
         ...     inventory[partnum] = record._replace(price=newprices[partnum], timestamp=time.now())
 
-.. attribute:: somenamedtuple._source
-
-    A string with the pure Python source code used to create the named
-    tuple class.  The source makes the named tuple self-documenting.
-    It can be printed, executed using :func:`exec`, or saved to a file
-    and imported.
-
-    .. versionadded:: 3.3
-
 .. attribute:: somenamedtuple._fields
 
     Tuple of strings listing the field names.  Useful for introspection

Doc/whatsnew/3.7.rst

@@ -435,6 +435,12 @@ API and Feature Removals
   Python 3.1, and has now been removed.  Use the :func:`~os.path.splitdrive`
   function instead.
 
+* :func:`collections.namedtuple` no longer supports the *verbose* parameter
+  or ``_source`` attribute which showed the generated source code for the
+  named tuple class.  This was part of an optimization designed to speed-up
+  class creation.  (Contributed by Jelle Zijlstra with further improvements
+  by INADA Naoki, Serhiy Storchaka, and Raymond Hettinger in :issue:`28638`.)
+
 * Functions :func:`bool`, :func:`float`, :func:`list` and :func:`tuple` no
   longer take keyword arguments.  The first argument of :func:`int` can now
   be passed only as positional argument.

Lib/collections/__init__.py

@@ -301,59 +301,9 @@ def __eq__(self, other):
 ### namedtuple
 ################################################################################
 
-_class_template = """\
-from builtins import property as _property, tuple as _tuple
-from operator import itemgetter as _itemgetter
-from collections import OrderedDict
+_nt_itemgetters = {}
 
-class {typename}(tuple):
-    '{typename}({arg_list})'
-
-    __slots__ = ()
-
-    _fields = {field_names!r}
-
-    def __new__(_cls, {arg_list}):
-        'Create new instance of {typename}({arg_list})'
-        return _tuple.__new__(_cls, ({arg_list}))
-
-    @classmethod
-    def _make(cls, iterable, new=tuple.__new__, len=len):
-        'Make a new {typename} object from a sequence or iterable'
-        result = new(cls, iterable)
-        if len(result) != {num_fields:d}:
-            raise TypeError('Expected {num_fields:d} arguments, got %d' % len(result))
-        return result
-
-    def _replace(_self, **kwds):
-        'Return a new {typename} object replacing specified fields with new values'
-        result = _self._make(map(kwds.pop, {field_names!r}, _self))
-        if kwds:
-            raise ValueError('Got unexpected field names: %r' % list(kwds))
-        return result
-
-    def __repr__(self):
-        'Return a nicely formatted representation string'
-        return self.__class__.__name__ + '({repr_fmt})' % self
-
-    def _asdict(self):
-        'Return a new OrderedDict which maps field names to their values.'
-        return OrderedDict(zip(self._fields, self))
-
-    def __getnewargs__(self):
-        'Return self as a plain tuple.  Used by copy and pickle.'
-        return tuple(self)
-
-{field_defs}
-"""
-
-_repr_template = '{name}=%r'
-
-_field_template = '''\
-    {name} = _property(_itemgetter({index:d}), doc='Alias for field number {index:d}')
-'''
-
-def namedtuple(typename, field_names, *, verbose=False, rename=False, module=None):
+def namedtuple(typename, field_names, *, rename=False, module=None):
     """Returns a new subclass of tuple with named fields.
 
     >>> Point = namedtuple('Point', ['x', 'y'])
@@ -390,46 +340,104 @@ def namedtuple(typename, field_names, *, verbose=False, rename=False, module=Non
                 or _iskeyword(name)
                 or name.startswith('_')
                 or name in seen):
-                field_names[index] = '_%d' % index
+                field_names[index] = f'_{index}'
             seen.add(name)
     for name in [typename] + field_names:
         if type(name) is not str:
             raise TypeError('Type names and field names must be strings')
         if not name.isidentifier():
             raise ValueError('Type names and field names must be valid '
-                             'identifiers: %r' % name)
+                             f'identifiers: {name!r}')
         if _iskeyword(name):
             raise ValueError('Type names and field names cannot be a '
-                             'keyword: %r' % name)
+                             f'keyword: {name!r}')
     seen = set()
     for name in field_names:
         if name.startswith('_') and not rename:
             raise ValueError('Field names cannot start with an underscore: '
-                             '%r' % name)
+                             f'{name!r}')
         if name in seen:
-            raise ValueError('Encountered duplicate field name: %r' % name)
+            raise ValueError(f'Encountered duplicate field name: {name!r}')
         seen.add(name)
 
-    # Fill-in the class template
-    class_definition = _class_template.format(
-        typename = typename,
-        field_names = tuple(field_names),
-        num_fields = len(field_names),
-        arg_list = repr(tuple(field_names)).replace("'", "")[1:-1],
-        repr_fmt = ', '.join(_repr_template.format(name=name)
-                             for name in field_names),
-        field_defs = '\n'.join(_field_template.format(index=index, name=name)
-                               for index, name in enumerate(field_names))
-    )
-
-    # Execute the template string in a temporary namespace and support
-    # tracing utilities by setting a value for frame.f_globals['__name__']
-    namespace = dict(__name__='namedtuple_%s' % typename)
-    exec(class_definition, namespace)
-    result = namespace[typename]
-    result._source = class_definition
-    if verbose:
-        print(result._source)
+    # Variables used in the methods and docstrings
+    field_names = tuple(map(_sys.intern, field_names))
+    num_fields = len(field_names)
+    arg_list = repr(field_names).replace("'", "")[1:-1]
+    repr_fmt = '(' + ', '.join(f'{name}=%r' for name in field_names) + ')'
+    tuple_new = tuple.__new__
+    _len = len
+
+    # Create all the named tuple methods to be added to the class namespace
+
+    s = f'def __new__(_cls, {arg_list}): return _tuple_new(_cls, ({arg_list}))'
+    namespace = {'_tuple_new': tuple_new, '__name__': f'namedtuple_{typename}'}
+    # Note: exec() has the side-effect of interning the typename and field names
+    exec(s, namespace)
+    __new__ = namespace['__new__']
+    __new__.__doc__ = f'Create new instance of {typename}({arg_list})'
+
+    @classmethod
+    def _make(cls, iterable):
+        result = tuple_new(cls, iterable)
+        if _len(result) != num_fields:
+            raise TypeError(f'Expected {num_fields} arguments, got {len(result)}')
+        return result
+
+    _make.__func__.__doc__ = (f'Make a new {typename} object from a sequence '
+                              'or iterable')
+
+    def _replace(_self, **kwds):
+        result = _self._make(map(kwds.pop, field_names, _self))
+        if kwds:
+            raise ValueError(f'Got unexpected field names: {list(kwds)!r}')
+        return result
+
+    _replace.__doc__ = (f'Return a new {typename} object replacing specified '
+                        'fields with new values')
+
+    def __repr__(self):
+        'Return a nicely formatted representation string'
+        return self.__class__.__name__ + repr_fmt % self
+
+    def _asdict(self):
+        'Return a new OrderedDict which maps field names to their values.'
+        return OrderedDict(zip(self._fields, self))
+
+    def __getnewargs__(self):
+        'Return self as a plain tuple.  Used by copy and pickle.'
+        return tuple(self)
+
+    # Modify function metadata to help with introspection and debugging
+
+    for method in (__new__, _make.__func__, _replace,
+                   __repr__, _asdict, __getnewargs__):
+        method.__qualname__ = f'{typename}.{method.__name__}'
+
+    # Build-up the class namespace dictionary
+    # and use type() to build the result class
+    class_namespace = {
+        '__doc__': f'{typename}({arg_list})',
+        '__slots__': (),
+        '_fields': field_names,
+        '__new__': __new__,
+        '_make': _make,
+        '_replace': _replace,
+        '__repr__': __repr__,
+        '_asdict': _asdict,
+        '__getnewargs__': __getnewargs__,
+    }
+    cache = _nt_itemgetters
+    for index, name in enumerate(field_names):
+        try:
+            itemgetter_object, doc = cache[index]
+        except KeyError:
+            itemgetter_object = _itemgetter(index)
+            doc = f'Alias for field number {index}'
+            cache[index] = itemgetter_object, doc
+        class_namespace[name] = property(itemgetter_object, doc=doc)
+
+    result = type(typename, (tuple,), class_namespace)
 
     # For pickling to work, the __module__ variable needs to be set to the frame
     # where the named tuple is created.  Bypass this step in environments where

Lib/test/test_collections.py

@@ -194,7 +194,6 @@ def test_factory(self):
         self.assertEqual(Point.__module__, __name__)
         self.assertEqual(Point.__getitem__, tuple.__getitem__)
         self.assertEqual(Point._fields, ('x', 'y'))
-        self.assertIn('class Point(tuple)', Point._source)
 
         self.assertRaises(ValueError, namedtuple, 'abc%', 'efg ghi')       # type has non-alpha char
         self.assertRaises(ValueError, namedtuple, 'class', 'efg ghi')      # type has keyword
@@ -366,11 +365,37 @@ def test_name_conflicts(self):
         newt = t._replace(itemgetter=10, property=20, self=30, cls=40, tuple=50)
         self.assertEqual(newt, (10,20,30,40,50))
 
-        # Broader test of all interesting names in a template
-        with support.captured_stdout() as template:
-            T = namedtuple('T', 'x', verbose=True)
-        words = set(re.findall('[A-Za-z]+', template.getvalue()))
-        words -= set(keyword.kwlist)
+       # Broader test of all interesting names taken from the code, old
+       # template, and an example
+        words = {'Alias', 'At', 'AttributeError', 'Build', 'Bypass', 'Create',
+        'Encountered', 'Expected', 'Field', 'For', 'Got', 'Helper',
+        'IronPython', 'Jython', 'KeyError', 'Make', 'Modify', 'Note',
+        'OrderedDict', 'Point', 'Return', 'Returns', 'Type', 'TypeError',
+        'Used', 'Validate', 'ValueError', 'Variables', 'a', 'accessible', 'add',
+        'added', 'all', 'also', 'an', 'arg_list', 'args', 'arguments',
+        'automatically', 'be', 'build', 'builtins', 'but', 'by', 'cannot',
+        'class_namespace', 'classmethod', 'cls', 'collections', 'convert',
+        'copy', 'created', 'creation', 'd', 'debugging', 'defined', 'dict',
+        'dictionary', 'doc', 'docstring', 'docstrings', 'duplicate', 'effect',
+        'either', 'enumerate', 'environments', 'error', 'example', 'exec', 'f',
+        'f_globals', 'field', 'field_names', 'fields', 'formatted', 'frame',
+        'function', 'functions', 'generate', 'get', 'getter', 'got', 'greater',
+        'has', 'help', 'identifiers', 'index', 'indexable', 'instance',
+        'instantiate', 'interning', 'introspection', 'isidentifier',
+        'isinstance', 'itemgetter', 'iterable', 'join', 'keyword', 'keywords',
+        'kwds', 'len', 'like', 'list', 'map', 'maps', 'message', 'metadata',
+        'method', 'methods', 'module', 'module_name', 'must', 'name', 'named',
+        'namedtuple', 'namedtuple_', 'names', 'namespace', 'needs', 'new',
+        'nicely', 'num_fields', 'number', 'object', 'of', 'operator', 'option',
+        'p', 'particular', 'pickle', 'pickling', 'plain', 'pop', 'positional',
+        'property', 'r', 'regular', 'rename', 'replace', 'replacing', 'repr',
+        'repr_fmt', 'representation', 'result', 'reuse_itemgetter', 's', 'seen',
+        'self', 'sequence', 'set', 'side', 'specified', 'split', 'start',
+        'startswith', 'step', 'str', 'string', 'strings', 'subclass', 'sys',
+        'targets', 'than', 'the', 'their', 'this', 'to', 'tuple', 'tuple_new',
+        'type', 'typename', 'underscore', 'unexpected', 'unpack', 'up', 'use',
+        'used', 'user', 'valid', 'values', 'variable', 'verbose', 'where',
+        'which', 'work', 'x', 'y', 'z', 'zip'}
         T = namedtuple('T', words)
         # test __new__
         values = tuple(range(len(words)))
@@ -396,30 +421,15 @@ def test_name_conflicts(self):
         self.assertEqual(t.__getnewargs__(), values)
 
     def test_repr(self):
-        with support.captured_stdout() as template:
-            A = namedtuple('A', 'x', verbose=True)
+        A = namedtuple('A', 'x')
         self.assertEqual(repr(A(1)), 'A(x=1)')
         # repr should show the name of the subclass
         class B(A):
             pass
         self.assertEqual(repr(B(1)), 'B(x=1)')
 
-    def test_source(self):
-        # verify that _source can be run through exec()
-        tmp = namedtuple('NTColor', 'red green blue')
-        globals().pop('NTColor', None)          # remove artifacts from other tests
-        exec(tmp._source, globals())
-        self.assertIn('NTColor', globals())
-        c = NTColor(10, 20, 30)
-        self.assertEqual((c.red, c.green, c.blue), (10, 20, 30))
-        self.assertEqual(NTColor._fields, ('red', 'green', 'blue'))
-        globals().pop('NTColor', None)          # clean-up after this test
-
     def test_keyword_only_arguments(self):
         # See issue 25628
-        with support.captured_stdout() as template:
-            NT = namedtuple('NT', ['x', 'y'], verbose=True)
-        self.assertIn('class NT', NT._source)
         with self.assertRaises(TypeError):
             NT = namedtuple('NT', ['x', 'y'], True)
 

Misc/NEWS.d/next/Library/2017-09-08-14-31-15.bpo-28638.lfbVyH.rst

@@ -0,0 +1,9 @@
+Changed the implementation strategy for collections.namedtuple() to
+substantially reduce the use of exec() in favor of precomputed methods. As a
+result, the *verbose* parameter and *_source* attribute are no longer
+supported.  The benefits include 1) having a smaller memory footprint for
+applications using multiple named tuples, 2) faster creation of the named
+tuple class (approx 4x to 6x depending on how it is measured), and 3) minor
+speed-ups for instance creation using __new__, _make, and _replace.  (The
+primary patch contributor is Jelle Zijlstra with further improvements by
+INADA Naoki, Serhiy Storchaka, and Raymond Hettinger.)