diff options
Diffstat (limited to 'Doc/reference/expressions.rst')
| -rw-r--r-- | Doc/reference/expressions.rst | 21 |
1 files changed, 14 insertions, 7 deletions
diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst index cdb802a..d074ebb 100644 --- a/Doc/reference/expressions.rst +++ b/Doc/reference/expressions.rst @@ -639,13 +639,13 @@ slots for which no default value is specified, a :exc:`TypeError` exception is raised. Otherwise, the list of filled slots is used as the argument list for the call. -.. note:: +.. impl-detail:: - An implementation may provide built-in functions whose positional parameters do - not have names, even if they are 'named' for the purpose of documentation, and - which therefore cannot be supplied by keyword. In CPython, this is the case for - functions implemented in C that use :cfunc:`PyArg_ParseTuple` to parse their - arguments. + An implementation may provide built-in functions whose positional parameters + do not have names, even if they are 'named' for the purpose of documentation, + and which therefore cannot be supplied by keyword. In CPython, this is the + case for functions implemented in C that use :cfunc:`PyArg_ParseTuple` to + parse their arguments. If there are more positional arguments than there are formal parameter slots, a :exc:`TypeError` exception is raised, unless a formal parameter using the syntax @@ -1053,6 +1053,8 @@ cross-type comparison is not supported, the comparison method returns supported cross-type comparisons and unsupported comparisons. For example, ``Decimal(2) == 2`` and `2 == float(2)`` but ``Decimal(2) != float(2)``. +.. _membership-test-details: + The operators :keyword:`in` and :keyword:`not in` test for membership. ``x in s`` evaluates to true if *x* is a member of *s*, and false otherwise. ``x not in s`` returns the negation of ``x in s``. All built-in sequences and set types @@ -1069,7 +1071,12 @@ return ``True``. For user-defined classes which define the :meth:`__contains__` method, ``x in y`` is true if and only if ``y.__contains__(x)`` is true. -For user-defined classes which do not define :meth:`__contains__` and do define +For user-defined classes which do not define :meth:`__contains__` but do define +:meth:`__iter__`, ``x in y`` is true if some value ``z`` with ``x == z`` is +produced while iterating over ``y``. If an exception is raised during the +iteration, it is as if :keyword:`in` raised that exception. + +Lastly, the old-style iteration protocol is tried: if a class defines :meth:`__getitem__`, ``x in y`` is true if and only if there is a non-negative integer index *i* such that ``x == y[i]``, and all lower integer indices do not raise :exc:`IndexError` exception. (If any other exception is raised, it is as |