from django.core.files import File
import os

f = open(tmp_path, 'w')
f.write(some_text)
f.close()
f = open(tmp_path)
dj_f = File(f)
model_object.file.save('file', dj_f)
f.close()
os.remove(tmp_path)

f = open(tmp_path, 'w')
f.write(some_text)
f.close()
setattr(model_object, 'file', tmp_path)
model_object.save()

path = grt_file_path(model_object)
f = open(MEDIA_ROOT + path, 'w')
f.write(some_text)
f.close()
setattr(model_object, 'file', path)
model_object.save()