How do I to flush redis db from python redis?

Yes, flushdb() and flushall() both exist.

check out this page, you will find them.

You can try also.

r.execute_command('FLUSHALL ASYNC') # delete keys in background

FLUSHALL ASYNC (Redis 4.0.0 or greater)

Redis is now able to delete keys in the background in a different thread without blocking the server. An ASYNC option was added to FLUSHALL and FLUSHDB in order to let the entire dataset or a single database to be freed asynchronously.

r.flushdb() # Delete all keys of currently selected database instance.
r.flushall() # Delete all keys of entire database.  

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Further reading : Redis FLUSHALL ASYNC

Redis-py actually has this functionality:

import redis
r = redis.Redis()
r.flushdb()