[Tutor] how to read and write to a file

Wed Jan 25 18:00:32 CET 2012

On Wed, Jan 25, 2012 at 11:30 AM, ken brockman <krush1954 at yahoo.com> wrote:
> Okay, got ya. Mea Culpa.
> Being misanthropic by nature I've not used or engaged  in a interactive
> forum such as this one before .
> I do grasp that a list is more then just the information it contains. So,
> does that mean i go with pickling? And can I save  two lists in one pickled
> file, or no?
>
> Thanks one and all, for the help.
> Ken
> ________________________________
> From: Joel Goldstick <joel.goldstick at gmail.com>
> To: ken brockman <krush1954 at yahoo.com>
> Cc: tutor at python.org
> Sent: Wednesday, January 25, 2012 11:04 AM
>
> Subject: Re: [Tutor] how to read and write to a file
>
> On Wed, Jan 25, 2012 at 10:50 AM, ken brockman <krush1954 at yahoo.com> wrote:
>> Thank you Joel and Alexander for your time and input.
>> I had just wanted to be able to store a list and read and write to it. But
>> it seems reading and writing is no go with lists, only strings, or no? Is
>> there a simply way I can tweak the read write feature to do lists? I'm
>> sorry
>> if I seem a tad slow on the uptick, I'm just starting to get
>> into programming and being up all night is not helping my comprehension
>> skills none.  I've not as yet tried either of your suggestions, but from
>> what I can gather pickling is not the right tool for the job at hand. I'm
>> not looking to have it read by another program nor send it over a network.
>>
>> Also I have two lists and two files. Is it possible to store both lists in
>> one file? I wouldn't imagine you could, but hey, doesn't hurt to ask.
>> Thanks again.
>>
>> Ken
>>
>> ________________________________
>> From: Joel Goldstick <joel.goldstick at gmail.com>
>> To: Alexander <rhettnaxel at gmail.com>
>> Cc: ken brockman <krush1954 at yahoo.com>; tutor at python.org
>> Sent: Wednesday, January 25, 2012 9:54 AM
>>
>> Subject: Re: [Tutor] how to read and write to a file
>>
>> On Wed, Jan 25, 2012 at 9:14 AM, Alexander <rhettnaxel at gmail.com> wrote:
>>> On Wed, Jan 25, 2012 at 8:32 AM, ken brockman <krush1954 at yahoo.com>
>>> wrote:
>>>>
>>>>
>>>> ________________________________
>>>> From: Alexander <rhettnaxel at gmail.com>
>>>> To: ken brockman <krush1954 at yahoo.com>
>>>> Cc: "tutor at python.org" <tutor at python.org>
>>>> Sent: Wednesday, January 25, 2012 7:38 AM
>>>> Subject: Re: [Tutor] how to read and write to a file
>>>>
>>>>
>>>>
>>>> On Wed, Jan 25, 2012 at 7:19 AM, ken brockman <krush1954 at yahoo.com>
>>>> wrote:
>>>>
>>>> I would like to write to and read from a file from python. I wanted to
>>>> use the file to save input to the program in a list. I have been looking
>>>> around and there seems to be several ways to go about it. I tried
>>>> pickling,
>>>> but am having an issue with it. What would be the correct way to
>>>> accomplish
>>>> this? I have tried several ways, but to no avail. I get no error msg.
>>>> but
>>>> the list isn't retaining the info. Is pickling even the best way to do
>>>> it.
>>>>
>>>> file1 = open("ArtyKlikes.p", "ab")  # likesList
>>>> file2 = open("ArtyDislikes.p", "ab")  # dislikes
>>>>
>>>> pickle.dump(likesList, file1)
>>>> pickle.dump(dislikeList, file2)
>>>>
>>>> file1.close()
>>>> file2.close()
>>>>
>>>> Any help would be greatly appreciated.
>>>>
>>>> _______________________________________________
>>>> Tutor maillist  -  Tutor at python.org
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>>>>
>>>>
>>>> Hi Ken. If you just want to read and write from a text file then you
>>>> don't need to pickle.
>>>> For example,
>>>> (the file info.txt exists)
>>>>
>>>> >>>fh = open ( 'info.txt', 'w' )
>>>> >>>fh.write ( 'peter piper picked a pack of pickled peppers.' )
>>>> >>>fh.close()
>>>> >>>fr = open ( 'info.txt', 'r')
>>>> >>>fr.readline()
>>>> 'peter piper picked a pack of pickled peppers.'
>>>> >>>fr.close()
>>>>
>>>> or whatever.
>>>> But do you have a need to use pickling?
>>>> --
>>>> Alexander
>>>> 7D9C597B
>>>>
>>>>
>>>> --------------------------------------------------------------------------
>>>>
>>>> Hey Alexander,
>>>> I had to try it before I went to sleep.
>>>> No good. I got an error msg. TypeError: must be str, not list.
>>>> So I guess that may be why i had went with pickling. I needed something
>>>> that would work with a list. Unless there is some other way?
>>>> Thanks again for taking the time to help out.
>>>>
>>>> Ken
>>>>
>>>>
>>> Ken, pickling is used when one wants to send information through a
>>> network or communicate with a database. Somebody else here knows more
>>> about pickling than I do. As for your list problem... I'm not exactly
>>> certain what you're trying to do. But I'm going with the idea that you
>>> have two files of information, one contains strings you like, and the
>>> other contains strings you dislike. And you want to read and write
>>> this information using Python.
>>>
>>>>>> like = [ 'orange', 'blue', 'red' ] #things I like
>>>>>> dislike = [ 'apples', 'bronze', 'bananas' ] #things I dislike
>>>>>> fh = open ( 'likes.txt', 'w' ) #let's open a file stream to write
>>>
>>> # fh is my shorthand for "file handle"
>>> #writing a list to a file stream:
>>>
>>>>>> for index in range( len( like )):
>>> fh.write( like[ index ] )
>>> fh.write ( '\n' ) #here i add a new line, maybe somebody else
>>> #knows a better way to avoid this?
>>>
>>>>>> fh.close()
>>>
>>> #now let's read that information into a list
>>>>>> fr = open ( 'info.txt' ) #I'm using python 3.2
>>>>>> mylistoflikes = fr.readlines()
>>>>>> mylistoflikes
>>> [ 'orange\n' , 'blue\n' , 'red\n' ]
>>>>>> fr.close()
>>>
>>> --
>>> Alexander
>>> 7D9C597B
>>> _______________________________________________
>>> Tutor maillist  -  Tutor at python.org
>>> To unsubscribe or change subscription options:
>>> http://mail.python.org/mailman/listinfo/tutor
>>
>> First, pickle is used to store data objects.  If you just want to
>> store text, you just write it and read it back from your file.  But
>> there are situations where you want to save an object.  Maybe you want
>> to have it available to another program.
>>
>> So, you nearly got through your example.  You pickled your lists, and
>> stored them, but you didn't retrieve them.
>>
>> Here is a link to review: http://wiki.python.org/moin/UsingPickle
>>
>> Here is my version of your program.  It worked for me.  copy and paste
>> it in a file, and try it
>> -----------------------------------------------
>> import pickle
>>
>>
>> ArtyKlikes = (1,2,3)
>> ArtyKDislikes = (4,5,6)
>>
>> file1 = open("ArtyKlikes.p", "ab")  # likesList
>> file2 = open("ArtyDislikes.p", "ab")  # dislikes
>>
>> pickle.dump(ArtyKlikes, file1)
>> pickle.dump(ArtyKDislikes, file2)
>>
>> file1.close()
>> file2.close()
>>
>> ArtyLikes = pickle.load(open("ArtyKlikes.p", 'rb'))
>> ArtyDisLikes = pickle.load(open("ArtyDislikes.p", 'rb'))
>>
>> print ArtyLikes
>> print ArtyDisLikes
>>
>> --
>> Joel Goldstick
>>
>>
> Ken,
>
> First of all, always remember to reply to all on the list.  That keeps
> everyone in the loop.
> Second, don't 'top post'.  Write your comments at the end of the
> thread so that people can follow the conversation.  Sometimes its
> useful to intersperse comments in someone's previous email.
>
> Writing text to a file and reading it is useful, and pretty easy to
> understand.  But when you say you want to write a list you have to
> start to understand what a list really is (or a dict or some other
> object).  A list is not only the values in the list, it is also the
> code that lets a list do what lists do.  Things like:
>
>   for something in mylist:
>       # do something with 'something'
> or:
>   print mylist[2]
>
> and so on.
>
> So, pickle is doing a whole lot more than writing '(1,2,3)' to your
> file.  It knows it is a list and it stores all it needs to about the
> list, including your specific list items.
>
>
>
>
>
>
> --
> Joel Goldstick
>
>
Go to the link I listed above.  It has examples.  I think you can use
one file and keep writing pickles to it.  But I've not used pickling,
so if it was me I would play around with it and see what you find out.
 The link has a simple example and other links to more complex
situations.


-- 
Joel Goldstick