Please keep your reply on the list, unless you have something private to say.
That way others can help, or learn from your questions. I've taken the liberty
of putting this back into the list.
Leam Hall wrote:
On 04/01/2012 09:40 PM, Steven D'Aprano wrote:
leam hall wrote:
Python 2.4.3 on Red Hat 5. Trying to use strip to remove characters
but it doesn't seem to work like I thought.
res = subprocess.Popen(['uname', '-a'], stdout=subprocess.PIPE)
uname = res.stdout.read().strip()
For future reference, you should identify the shortest possible amount
of code that demonstrates the problem. See also http://sscce.org/
You are asking a question about string.strip(). Where the string comes
from is irrelevant -- there's no need to use an example as complicated
as the above, when a simple string constant will do the job perfectly.
So the shortest possible amount of code to demonstrate your problem is a
single method call:
>>> 'spam ham 1:2:3 eggs'.strip(':')
'spam ham 1:2:3 eggs'
All the stuff with subprocess.Popen and reading from stout and whatnot
doesn't have anything to do with the issue at hand. It cannot shed any
light on the problem; at best it must be ignored, at worst it may
confuse the issue.
As others have already explained, strip() does not remove characters
from anywhere in the string, it strips them from the ends only.
There is also a lstrip() and rstrip() for times you only want to remove
them from the left or right side.
Steve,
How does one minimize the example code when one doesn't know the
problem? The short example seemed to work, the long one didn't. So the
options seemed to be that the long code changed the expected behavior,
the long code was transcribed incorrectly, or I misunderstood something.
At the point of asking the question I didn't know which of those was the
issue.
That's a good question. Being able to diagnose errors or unexpected behaviour
is an absolutely critical skill for a programmer. So how could you have
diagnosed this (apparent) error?
(Apart from reading the Fine Manual, of course.)
You started off by reading some data with the subprocess module. So the first
thing to do is to replace the calls
res = subprocess.Popen(['uname', '-a'], stdout=subprocess.PIPE)
uname = res.stdout.read().strip()
with a single assignment using the exact same string:
uname = 'Linux ando 2.6.18-53.el5 #1 SMP Mon Nov 12 02:22:48 EST 2007 i686
i686 i386 GNU/Linux'
(The above should be a single line; my mail client wraps it over two lines.)
Does the problem still exist? Yes:
>>> uname.strip(':') # I expect the colons to disappear.
'Linux ando 2.6.18-53.el5 #1 SMP Mon Nov 12 02:22:48 EST 2007 i686 i686 i386
GNU/Linux'
And lo, the colons don't disappear. The "problem" (as you saw it) continues.
Clearly the problem has nothing to do with the *source* of the string. (It
would be a bizarre and strange situation if it did!)
Step two: Simplify simplify simplify. Why use 85 characters when fewer than a
dozen will do? Cut out all the irrelevant bits of the string:
>>> uname = '02:22:48'
>>> uname.strip(':')
'02:22:48'
No change in the mysterious behaviour.
At this point you have your short, simple example:
>>> '02:22:48'.strip(':') # I expect '022248'
'02:22:48'
and you can ask for help. Or if you are keen to solve this yourself, you could
try different strings and see if you can work out what's going on:
>>> '0222:48'.strip(':') # maybe it works with only 1 colon?
'0222:48'
>>> '022248:'.strip(':') # or perhaps if I move the colon somewhere else?
'022248'
>>> ':02:22:48:'.strip(':') # which colons will be removed?
'02:22:48'
--
Steven
_______________________________________________
Tutor maillist - Tutor@python.org
To unsubscribe or change subscription options:
http://mail.python.org/mailman/listinfo/tutor
