What is the EAFP principle in Python?

Question

What is meant by \"using the EAFP principle\" in Python? Could you provide any examples?

Answer 1

I'll try to explain it with another example.

Here we're trying to access the file and print the contents in console.

LBYL - Look Before You Leap :

We might want to check if we can access the file and if we can, we'll open it and print the contents. If we can't access the file we'll hit the else part. The reason that this is a race condition is because we first make an access-check. By the time we reach with open(my_file) as f: maybe we can't access it anymore due to some permission issues (for example another process gains an exclusive file lock). This code will likely throw an error and we won't be able to catch that error because we thought that we could access the file.

import os

my_file = "/path/to/my/file.txt"

# Race condition
if os.access(my_file, os.R_OK):
    with open(my_file) as f:
        print(f.read())
else:
    print("File can't be accessed")

EAFP - Easier to Ask for Forgiveness than Permission :

In this example, we're just trying to open the file and if we can't open it, it'll throw an IOError. If we can, we'll open the file and print the contents. So instead of asking something we're trying to do it. If it works, great! If it doesn't we catch the error and handle it.

# # No race condition
try:
    f = open(my_file)
except IOError as e:
    print("File can't be accessed")
else:
    with f:
        print(f.read())