One useful trick I have seen and used is a Logging facility.
The code is liberally sprinkled with "print"s but with varying levels assigned to them so at run time a parameter can be set to log in "verbose" mode: or detailing every step of the program, or varying modes all the way to "silent" where no logging takes place.

"That that is, is... for what is that but that? and is but is?" Shakespeare, Twelfth Night, Act IV, Scene 2 "Yet THAT which is not neither is nor is not That which is!" Frater Perdurabo (pseud. Aleister Crowley), Liber CCCXXXIII, The Book of Lies