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
– apingaway, Commented Apr 30, 2022 at 4:29
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
– Ulrich Eckhardt, Commented Apr 30, 2022 at 7:58

Jordan Bonecutter · Accepted Answer · 2022-04-29 18:21:32Z

5

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, 2022 at 18:21

Jordan Bonecutter

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Comments

Sören · Accepted Answer · 2022-04-30 07:55:02Z

2

You can use not s:

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

answered Apr 29, 2022 at 18:21

Sören

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scotscotmcc · Accepted Answer · 2022-04-29 18:28:53Z

0

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

isinstance(s,str)

answered Apr 29, 2022 at 18:28

scotscotmcc

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Why would you think that's the case? OP even type-hinted s to be a string!