cb_3.py

import pytorch_lightning as pl

class MyAPICallback(pl.Callback):

    def on_init_start(self, trainer):
        requests.post('model started')

    def on_init_end(self, trainer):
        

    def on_train_end(self, trainer, pl_module):
        data = requests.get('/new_data/or/something')
        save(data)
        ...

# pass to trainer
trainer = pl.Trainer(callbacks=[MyPrintingCallback()])