how to check for non null string in python?

Question

Total newbie python question. I find myself having to write to the following code

s: str
if s is None or len(s) <= 0

to check for string validation.

I finally wrote a tiny function to do that for me.

Is there a more pythantic way of doing this?

I am curious about the function you are mentioning. Would you also post it here, I think it will be useful to have it? — apingaway, Apr 30 '22 at 04:29
Other than in C, a string can not be null. A string can be empty and a variable can reference `None`, but that's about it. I would expect type annotations to be able to guarantee that a variable is a `str` and not `None`, where does that fail for you? — Ulrich Eckhardt, Apr 30 '22 at 07:58

score 3 · Accepted Answer · answered Apr 29 '22 at 18:21

3

The string will be "truthy" if it is not None or has len > 0. Simply do the following check:

if s:
  print("The string is valid!")

answered Apr 29 '22 at 18:21

Jordan Bonecutter

Sören · Answer 2 · 2022-04-30T07:55:02.177

1

You can use not s:

>>> not None
True
>>> not ''
True
>>> not 'foo'
False

edited Apr 30 '22 at 07:55

answered Apr 29 '22 at 18:21

Sören

score 0 · Answer 3 · answered Apr 29 '22 at 18:28

0

If your real goal is to find out if s is a string, you can use isinstance().

isinstance(s,str)

answered Apr 29 '22 at 18:28

scotscotmcc

Why would you think that's the case? OP even type-hinted s to be a string! – Sören Apr 29 '22 at 18:30

3 Answers3