How to know if document exists in firestore python?

If you're using firebase-admin:

fs.collection('items').document('item-id').get().exists

True iff items/item-id exists.

Alternatively

'item-id' in (d.id for d in fs.collection('items').get())

A much simpler and memory efficient approach:

doc_ref = db.collection('my_collection').document('my_document')
doc = doc_ref.get()
if doc.exists:
    logging.info("Found")
else:
    logging.info("Not found")

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