The patch applied to the default branch should be reverted.

The 2.7 _hotshot extension module follows the specifications of PyEval_SetTrace:

  """Set the tracing function to func. This is similar to PyEval_SetProfile(),
  except the tracing function does receive line-number events."""
                              ^^^^^^^^^^^^

The 2.7 patch breaks test_hotshot because PyTrace_LINE events are not sent
anymore when f_trace is NULL.

The first patch (already applied to the default branch), breaks also existing
applications that expect to receive line events when they don't care to
implement the following semantics defined by sys.settrace:

  """The trace function is invoked (with event set to 'call') whenever a new
     local scope is entered; it should return a reference to a local trace
     function to be used that scope, or None if the scope shouldn’t be
     traced."""

Those applications want to receive unconditionally line debug events.

Attached is a patch that reverts the patch on the default branch.