Emacs Delete Lines

Sometimes when i write small scripts i tend to insert print statements for debugging. After i verified the correctness of my program i want to get rid of all unnecessary debug statements. With Emacs you can delete all lines which match a specific regular expression with M-x flush-lines or with its alias M-x delete-matching-lines. Interactively you can enter your regular expression and all matching lines will be deleted from you cursor position downwards.