Re: Remove empty strings from list
Thanks Chris! Thanks for the quick reply. Indeed this is the case! I have
now written out a new list, instead of modifying the list I am iterating
over.
Logged at my blog:
http://learnwithhelvin.blogspot.com/2009/09/python-loop-and-modify-list.html
Regards,
Helvin =)
On Tue, Sep 15, 2009 at 1:55 PM, Chris Rebert c...@rebertia.com wrote:
On Mon, Sep 14, 2009 at 6:49 PM, Helvin helvin...@gmail.com wrote:
Hi,
Sorry I did not want to bother the group, but I really do not
understand this seeming trivial problem.
I am reading from a textfile, where each line has 2 values, with
spaces before and between the values.
I would like to read in these values, but of course, I don't want the
whitespaces between them.
I have looked at documentation, and how strings and lists work, but I
cannot understand the behaviour of the following:
line = f.readline()
line = line.lstrip() # take away whitespace at the
beginning of the
readline.
list = line.split(' ') # split the str line into a
list
# the list has empty strings in it, so now,
remove these empty strings
for item in list:
if item is ' ':
print 'discard these: ',item
index = list.index(item)
del list[index] # remove
this item from the list
else:
print 'keep this: ',item
The problem is, when my list is : ['44', '', '', '', '', '',
'0.0\n']
The output is:
len of list: 7
keep this: 44
discard these:
discard these:
discard these:
So finally the list is: ['44', '', '', '0.0\n']
The code above removes all the empty strings in the middle, all except
two. My code seems to miss two of the empty strings.
Would you know why this is occuring?
Block quoting from http://effbot.org/zone/python-list.htm
Note that the for-in statement maintains an internal index, which is
incremented for each loop iteration. This means that if you modify the
list you’re looping over, the indexes will get out of sync, and you
may end up skipping over items, or process the same item multiple
times.
Thus why your code is skipping over some elements and not removing them.
Moral: Don't modify a list while iterating over it. Use the loop to
create a separate, new list from the old one instead.
Cheers,
Chris
--
http://blog.rebertia.com
--
Helvin
Though the world may promise me more, I'm just made to be filled with the
Lord.
--
http://mail.python.org/mailman/listinfo/python-list
Re: global variable not working inside function. Increment
Wow!!! Thanks a million!! It worked! = DThanks for the fast reply too! Helvin On Sat, Sep 5, 2009 at 11:52 AM, Rami Chowdhury rami.chowdh...@gmail.comwrote: global no_picked no_picked = 0 def picked(object, event): no_picked += 1 print no_picked In order to be able to affect variables in the global scope, you need to declare them global inside the function, and not at the global scope. So your code should read: no_picked = 0 def picked(object, event): global no_picked no_picked += 1 print no_picked I believe that will work. On Fri, 04 Sep 2009 16:43:27 -0700, Helvin helvin...@gmail.com wrote: Hi, This increment thing is driving me nearly to the nuts-stage. I have a function that allows me to pick points. I want to count the number of times I have picked points. global no_picked no_picked = 0 def picked(object, event): no_picked += 1 print no_picked Error msg says: UnboundLocalError: local variable 'no_picked' referenced before assignment For some reason, no_picked does not increment, but the printing statement works. Do you know why? (I'm actually writing this for a vtkrenderwindowinteractor.) Helvin -- Rami Chowdhury Never attribute to malice that which can be attributed to stupidity -- Hanlon's Razor 408-597-7068 (US) / 07875-841-046 (UK) / 0189-245544 (BD) -- Helvin Though the world may promise me more, I'm just made to be filled with the Lord. -- http://mail.python.org/mailman/listinfo/python-list
Re: string find mystery
Thanks! I just realised that too, but I used the condition:.find() 0 But I think your's is better. Simple programming knowledge... I made a blog post: http://learnwithhelvin.blogspot.com/2009/09/1-is-true-if-loops.html http://learnwithhelvin.blogspot.com/2009/09/1-is-true-if-loops.html On Thu, Sep 3, 2009 at 5:19 PM, Stephen Hansen apt.shan...@gmail.comwrote: The amazing thing is when file_str = 'C:\Qt\SimLCM\Default \Data_Input_Material.txt', the first if statement if fulfilled, that seemingly says that in this file_str, python actually finds the word 'Geometry'. I know this, because the line: 'I found geometry' is printed. However, if instead of using file_str.find(), I use file_str.endswith(), it does not exhibit this strange behaviour. The problem is str.find returns -1 on failure; and -1 is a true value. Only 0, empty string, empty sequences, etc, are false values. So, you have to test, 'if find_str.find(pattern) != -1:' HTH, --S -- Helvin Though the world may promise me more, I'm just made to be filled with the Lord. -- http://mail.python.org/mailman/listinfo/python-list
