How to throw error and exit with a custom message in python

Question

I’ve seen people suggesting sys.exit() in Python.
My question is that, is there any other way to exit the execution of current script, I mean termination, with an error.

Something like this:

sys.exit("You can not have three process at the same time.")

Currently my solution would be:

print("You can not have three process at the same time.")
sys.exit()

Asked By: Mostafa Talebi

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Source

Answer 1

Calling sys.exit with a string will work. The docs mention this use explicitly:

In particular, sys.exit(“some error message”) is a quick way to exit a program when an error occurs.

Answered By: lvc

Answer 2

You can also raise an error like this:

raise SystemExit('Error: 3 processes cannot run simultaneously.')

One advantage of this approach is that you don’t have to import the Python sys module. This works on Linux with Python 3 and Python 2. I have not tested it on Windows or Mac OS.

Answered By: Osian

Answer 3

There are 3 approaches, the first as lvc mentioned is using sys.exit

sys.exit('My error message')

The second way is using print, print can write almost anything including an error message

print >>sys.stderr, "fatal error"     # Python 2.x
print("fatal error", file=sys.stderr) # Python 3.x

The third way is to rise an exception which I don’t like because it can be try-catch

  raise SystemExit('error in code want to exit')

it can be ignored like this

try:
  raise SystemExit('error in code want to exit')
except:
  print("program is still open")

Answered By: nima moradi

Answer 4

You have to use import sys first

Then use sys.exit("your custom error message")

Answered By: Dasun

How to throw error and exit with a custom message in python

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