What's the max length of a ListProperty?

Question

How many items can be stored in a ListProperty? Is there a limit?

Answer 1

Entities are limited to 1MB in size (when encoded as a Protocol Buffer), so this provides a practical limit on the size of a list. Further, if the list is indexed, you're limited to 5000 entries before you get an exception because your entity has too many index rows.

Answer 2

In my experience you will get MemoryError exceptions deserializing ListProperties before you hit a hard limit. That used to happen to me with 5,000 to 10,000 Key entities in the list.

Also, entities are limited to 5,000 indexed properties so 5,000 is a good maximum. (I feel like I used to have more sometimes but I don't remember exactly now.)