I am trying to call `bpy.ops.object.parent_clear` in blender background mode (no GUI) and it fails with an "context is incorrect" message. I would like to read the source code of the operator to better understand what is going on. I downloaded the source code of the blender 2.74 distribution. The error message indicates where the error occurs:

```
File ".../Resources/2.74/scripts/modules/bpy/ops.py", line 189, in  __call__
ret = op_call(self.idname_py(), None, kw)
RuntimeError: Operator bpy.ops.object.parent_clear.poll() failed, context is incorrect

```

However, at that location one can only find

```
ret = op_call(self.idname_py(), None, kw)

```

which is another call. Where do I find the actual implementation of `parent_clear`?