Transform datetime in YYYY-MM-DD HH:MM[:SS[.SSSSSS]]

If that's literally what you need.

now = datetime.now().strftime("%Y-%m-%d %H:%M[:%S[.%f]]")

More likely, the square brackets indicate optional parts. So:

now = datetime.now().strftime("%Y-%m-%d %H:%M")

or

now = datetime.now().strftime("%Y-%m-%d %H:%M:%S")

or

now = datetime.now().strftime("%Y-%m-%d %H:%M:%S.%f")