Python testing empty string

[rantanplan]

This is to aaaaaaalllllllll Fedorianer. The Universe is waiting for you. Particular Python is waiting.


Ok. The Question.
I'm new to it. I want to knwo how i can test if an argument in Python
sys.argv[1:] is empty ? Or even in general an string is empty ?
In C/C++ i use the compare against 0/NULL but this doesn't work in Python.

i wrote it this way


if sys.argv[1:] == "":
print "Please enter adress."

Btw, this is an official licenced Newbie question by ... Dumb&Nice Inc.

Thank you.

[Daverz]

Originally Posted by rantanplan

if sys.argv[1:] == "":
print "Please enter adress."

Yes, that's how you'd test for an empty string, but this assumes that what was entered on the command line was quoted to begin with:

[dmcook@localhost ~]$ /tmp/test.py -f "" -g ""
['/tmp/test.py', '-f', '', '-g', '']

Not too likely. If they just leave off the arguments, you'll see:

['/tmp/test.py', '-f', '-g']

So checking for an empty string is not too helpful.

Instead I suggest the optparse module, which I think has been standard since 2.3. It makes adding command-line options to your programs very easy.

http://docs.python.org/lib/module-optparse.html

[Jman]

You can also write it

if len(string) == 0

See the sequence reference

[rantanplan]

This was very helpful. Thank to you all.
I have the Documentation for Python but for some kind little nifty trick it's a huge
document to look. And sometimes it's to much information for an beginner if i look
for such 'easy' things like empty strings.
Does anyone know a good Python-Forum like this awesome Fedora Board ?
(Deutsch bevorzugt.) German preferred.

[marko]

The best practice, elegant way to test for an empty string like that would be
to replace

if len(string) == 0:

with the shorter code:

if not string:

REF see the Section 5.1 in the sequence reference in post 3, it shows that empty python sequences themselves resolve in the if statement in a logical way, so [], {}, or '' or None, etc --> False

[wattana]

Thanks Marko!!

This is a great tip!!

[jpollard]

Note: there is a difference between an empty string, and no string at all.