Question

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How to check if text is “empty” (spaces, tabs, newlines) in Python?

I am trying to write a short function to process lines of text in a file. When it encounters a line with significant content (meaning more than just whitespace), it is to do something with that line. The control structure I wanted was

if '\S' in line: do something

or

if r'\S' in line: do something

(I tried the same combinations with double quotes also, and yes I had imported re.) The if statement above, in all the forms I tried, always returns False. In the end, I had to resort to the test

if re.search('\S', line) is not None: do something

This works, but it feels a little clumsy in relation to a simple if statement. My question, then, is why isn’t the if statement working, and is there a way to do something as (seemingly) elegant and simple?

I have another question unrelated to control structures, but since my suspicion is that it is also related to a possibly illegal use of regular expressions, I’ll ask it here. If I have a string

s = ” \t\tsome text \t \n\n”

The code

s.strip('\s')

returns the same string complete with spaces, tabs, and newlines (r’\s’ is no different). The code

s.strip()

returns “some text”. This, even though strip called with no character string supposedly defaults to stripping whitespace characters, which to my mind is exactly what the expression ‘\s’ is doing. Why is the one stripping whitespace and the other not?

Thanks for any clarification.

Answer 1

Python string functions are not aware of regular expressions, so if you want to use them you have to use the re module.

However if you are only interested in finding out of a string is entirely whitespace or not, you can use the str.isspace() function:

>>> 'hello'.isspace()
False
>>> '  \n\t  '.isspace()
True