About imports

[Yourun-proger]

Hello! I have this tree:

/project_name
* app.py
* forms.py
* /templates

in my app.py i have code like this:

from forms import MySomeForm
#some code
if __name__ == '__main__':
    app.run()

What i do in cmd:

$ python app.py
>> All works!

$ flask run
>> `ModuleNotFoundError: No module named 'forms'`.

I change from forms to from .forms

$ flask run
>> All works!

python app.py
>> `ImportError: attempted relative import with no known parent package`

The crux of my question is whether this behavior is normal for a flask? Thank you!