internal_bisect_left and internal_bisect_right use PySequence_Size when a "hi" argument wasn't provided, which causes this silly error message:

    >>> bisect.bisect_right(dict.fromkeys(range(10)), 5)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: object of type 'dict' has no len()

They could use PyObject_Size and let PySequence_GetItem in the loop catch the error:

    >>> bisect.bisect_right(dict.fromkeys(range(10)), 5, 0, 10)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: 'dict' object does not support indexing

Since that actually makes sense and is more efficient / less verbose than adding a PySequence_Check.

It was fixed in issue32500. This is a new feature and it was not backported.

>>> bisect.bisect_right(dict.fromkeys(range(10)), 5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: dict is not a sequence
>>> bisect.bisect_right(dict.fromkeys(range(10)), 5, 0, 10)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: dict is not a sequence

Dan, thanks for the suggestion.  Changing to PyObject_Size() would have been the right thing to do if the error message had not been fixed.  But since the new error message "TypeError: dict is not a sequence" is more helpful than "TypeError: 'dict' object does not support indexing", we should leave the code as-is.