Document ImportCycleError and PyExc_ImportCycleError.

Author: Yhg1s

Doc/c-api/exceptions.rst

@@ -1108,6 +1108,8 @@ Exception types
      * :exc:`FloatingPointError`
    * * .. c:var:: PyObject *PyExc_GeneratorExit
      * :exc:`GeneratorExit`
+   * * .. c:var:: PyObject *PyExc_ImportCycleError
+     * :exc:`ImportCycleError`
    * * .. c:var:: PyObject *PyExc_ImportError
      * :exc:`ImportError`
    * * .. c:var:: PyObject *PyExc_IndentationError

Doc/library/exceptions.rst

@@ -266,6 +266,12 @@ The following exceptions are the exceptions that are usually raised.
 
    .. versionadded:: 3.6
 
+.. exception:: ImportCycleError
+
+   A subclass of :exc:`ImportError` which is raised when a lazy import fails
+   because it (directly or indirectly) tries to import itself.
+
+   .. versionadded:: 3.15
 
 .. exception:: IndexError