why writing list to file puts each item from list on seperate line?
steve at REMOVETHIScyber.com.au
Sat Dec 31 05:52:30 CET 2005
On Fri, 30 Dec 2005 20:22:52 -0800, homepricemaps wrote:
> if i use the code below to write a list to a file
> list = (food, price, store)
Why are you shadowing the built in type list? This is bad practice. Sooner
or later you will do this:
list = [1, 2, 3]
something = process(list)
... lots of code ...
# try to convert to a list
myList = list(something)
and then you'll spend ages trying to work out why list() raises an
> f = open(r"test.txt", 'a')
> f.write ( os.linesep.join( list ) )
> it outputs to a file like this
> star market
That's what you told it to do. Walk through the code:
>>> data = 
>>> L = ("apple", "0.49", "market")
[("apple", "0.49", "market")] # a list with one tuple
So far so good. But now watch:
>>> f = open(r"test.txt", 'a')
I hope you aren't opening the file EVERY time you want
to write a single line
Remember what L is: ("apple", "0.49", "market"). You now join that list
(actually a tuple) into a single string: "apple\n0.49\nmarket\n" and write
that string to the file.
What happened to data? It never gets used after you append to it.
> and i want it to do
> apple, .49. star market
Then what you want to do is change data to a list of strings rather than
a list of tuples. Before appending to data, you join the tuple ("apple",
"0.49", "market") like so:
data.append(", ".join(L) + "\n") # note newline at the end of each line
Then, after you have appended ALL the lines, you open your file once for
writing, and write data in one go:
Hope this helps.
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