“Ask forgiveness not permission” - explain

Question

I\'m not asking for personal \"religious\" opinions about this philosophy, rather something a bit more technical.

I understand this phrase is one of several litmus t

Answer 1

While there's already a number of high quality answers, most primarily discuss this from a stylistic stand point, as appose to a functional one.

There are certain cases where we need to ask forgiveness, not permission to insure correct code (outside of a multithreaded programs).

A canonical example being,

if file_exists: 
    open_it()

In this example, the file could have been deleted between the check and trying to actually open the file. This is avoided by using try:

try:
    open_it()
except FileNotFoundException:
    pass # file doesn't exist 

This crops up in a variety of places, often working with filesystems or external APIs.