How to merge objects in Blender using Python?

Question

Python

Problem: objects are not merged (Warning: Active object is not a selected mesh)
There is a large map with a huge number of objects on it.

It was necessary to merge objects that have the same beginning of the name
{"name", "name 1", (...),"name N"} -> "name"
Doing this by hand is quite long and dreary, so I decided to take the opportunity to write for python script blender.
Through trial and error, two methods were created:

import collections, time
def selector(): # выделяет объекты, названия которых начинаются одинаково
    c = collections.Counter([x.name.split()[0] for x in C.scene.objects])
    _nr = [x for x in dict(c) if dict(c)[x] > 1]
    del c
    for nr in _nr:
        bpy.ops.object.select_all(action='DESELECT')
        print("Selecting all", nr)
        for obj in C.scene.objects:
            if not obj.name.startswith(nr): continue
            bpy.data.objects[obj.name].select = True
            print("Selected", obj.name)
        joiner()

def joiner(): # должен объединять объекты
    bpy.ops.object.join()
    time.sleep(.5)
    bpy.ops.object.select_all(action='DESELECT')

When calling the selector() method, heaps of objects with the same name beginnings should be combined, but not:

I noticed that when selector() selects objects, all of them are highlighted in orange:

At the same time, if you call joiner() yourself, then it writes in the console :

Joining via Ctrl+J causes the same error (but it is displayed in the toolbar).
If you select manually, then there is always one element highlighted in yellow:

In this case, the call to joiner (), as well as joining via Ctrl + J, work with a bang. All objects merge into the one that was highlighted in yellow.
Can anyone come across?