[3.12] gh-116938: Clarify documentation of dict and dict.update r…

…egarding the positional argument they accept (GH-125213) (#125337)

Co-authored-by: Victorien <65306057+Viicos@users.noreply.github.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Doc/library/stdtypes.rst

@@ -4460,14 +4460,14 @@ can be used interchangeably to index the same dictionary entry.
  ``dict([('foo', 100), ('bar', 200)])``, ``dict(foo=100, bar=200)``
 
  If no positional argument is given, an empty dictionary is created.
- If a positional argument is given and it is a mapping object, a dictionary
- is created with the same key-value pairs as the mapping object. Otherwise,
- the positional argument must be an :term:`iterable` object. Each item in
- the iterable must itself be an iterable with exactly two objects. The
- first object of each item becomes a key in the new dictionary, and the
- second object the corresponding value. If a key occurs more than once, the
- last value for that key becomes the corresponding value in the new
- dictionary.
+ If a positional argument is given and it defines a ``keys()`` method, a
+ dictionary is created by calling :meth:`~object.__getitem__` on the argument with
+ each returned key from the method. Otherwise, the positional argument must be an
+ :term:`iterable` object. Each item in the iterable must itself be an iterable
+ with exactly two elements. The first element of each item becomes a key in the
+ new dictionary, and the second element the corresponding value. If a key occurs
+ more than once, the last value for that key becomes the corresponding value in
+ the new dictionary.
 
  If keyword arguments are given, the keyword arguments and their values are
  added to the dictionary created from the positional argument. If a key
@@ -4624,10 +4624,11 @@ can be used interchangeably to index the same dictionary entry.
  Update the dictionary with the key/value pairs from *other*, overwriting
  existing keys. Return ``None``.
 
- :meth:`update` accepts either another dictionary object or an iterable of
- key/value pairs (as tuples or other iterables of length two). If keyword
- arguments are specified, the dictionary is then updated with those
- key/value pairs: ``d.update(red=1, blue=2)``.
+ :meth:`update` accepts either another object with a ``keys()`` method (in
+ which case :meth:`~object.__getitem__` is called with every key returned from
+ the method). or an iterable of key/value pairs (as tuples or other iterables
+ of length two). If keyword arguments are specified, the dictionary is then
+ updated with those key/value pairs: ``d.update(red=1, blue=2)``.
 
  .. method:: values()
 

Lib/_collections_abc.py

@@ -973,7 +973,7 @@ def clear(self):
 
  def update(self, other=(), /, **kwds):
  ''' D.update([E, ]**F) -> None. Update D from mapping/iterable E and F.
- If E present and has a .keys() method, does: for k in E: D[k] = E[k]
+ If E present and has a .keys() method, does: for k in E.keys(): D[k] = E[k]
  If E present and lacks .keys() method, does: for (k, v) in E: D[k] = v
  In either case, this is followed by: for k, v in F.items(): D[k] = v
  '''