How to write List Object to a File??

[Alex Martelli]

<ed_tsang at yahoo.com> wrote in message
news:mailman.988151437.3004.python-list at python.org...
> I currently have a list and woulr like to store the contents into a
> text fiel whihc I can read back ...
>
> For example:
> a = ['a','b','c','d']

It's a list of strings, then?  Without newline characters at the
end?  And you want to write one per line?

> #do something like
> fd = open('txt.txt','w')
> fd.write(a)
> Traceback (innermost last):
>   File "<stdin>", line 1, in ?
> TypeError: read-only buffer, list
>
> What to do??

Maybe simplest
    fd.writelines([x+'\n' for x in a])
for some definition of "simplest".  You may expand the
loops differently of course, e.g.:
    for x in a
        fd.write(x+'\n')


If a is not a list of strings, you'll want to use str(x)
rather than x in either of the above examples.


> And I can't use pickle ...
>
> later on I would like to read it back...
>
> fd = open('txt.txt','r')
>
> iniInfo = fd.readlines()
> b=[]
> b = iniInfo[0]
> # copy list contents into c
> map(c.append,b)
>
> I think this also not work right

I think it will separately append each character of the
first line, though I haven't checked.

> ?
> Can someone kindly tell me how to do write and read a list to a file?

fd.readlines() gives you a list -- but each string does have a trailing
newline character of course.  You can take it out in many ways,
e.g. c.extend([x[:-1] for x in iniInfo])


Alex