Sorry, let's start again.
Here is a for loop operating on a list of string items:
data = ["string 1", "string 2", "string 3", "string 4", "string 5", "string 6",
"string 7", "string 8", "string 9", "string 10", "string 11"]
result = ""
for item in data:
result = <some operation on> item
print result
I want to replace the for loop with another structure to improve performance
(as the data list will contain >10,000 string items]. At each iteration of the
for loop the result is printed (in fact, the result is sent from the server to
a browser one result line at a time)
The for loop will be called continuously and this is another reason to look for
a potentially better structure preferably a built-in.
Hope this makes sense! Thank-you.
Dinesh
----- Original Message -----
From: Kent Johnson
To: Dinesh B Vadhia
Cc: tutor@python.org
Sent: Wednesday, April 09, 2008 12:40 PM
Subject: Re: [Tutor] List comprehensions
Dinesh B Vadhia wrote:
> Here is a for loop operating on a list of string items:
>
> data = ["string 1", "string 2", "string 3", "string 4", "string 5",
> "string 6", "string 7", "string 8", "string 9", "string 10", "string 11"]
>
> result = ""
> for item in data:
> result = item + "\n"
> print result
I'm not sure what your goal is here. Do you mean to be accumulating all
the values in data into result? Your sample code does not do that.
> I want to replace the for loop with a List Comrehension (or whatever) to
> improve performance (as the data list will be >10,000]. At each stage
> of the for loop I want to print the result ie.
>
> [print (item + "\n") for item in data]
>
> But, this doesn't work as the inclusion of the print causes an invalid
> syntax error.
You can't include a statement in a list comprehension. Anyway the time
taken to print will swamp any advantage you get from the list comp.
If you just want to print the items, a simple loop will do it:
for item in data:
print item + '\n'
Note this will double-space the output since print already adds a newline.
If you want to create a string with all the items with following
newlines, the classic way to do this is to build a list and then join
it. To do it with the print included, try
result = []
for item in data:
newItem = item + '\n'
print newItem
result.append(newItem)
result = ''.join(result)
Kent
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