[program-l] Re: Some thoughts on objects was ...Re: Re: Python, best way to return a bunch of data from a function?
- From: "Homme, James" <james.homme@xxxxxxxxxxxx>
- To: "program-l@xxxxxxxxxxxxx" <program-l@xxxxxxxxxxxxx>
- Date: Wed, 3 Oct 2012 13:51:39 +0000
Hi Al,
I think that maybe you would want to have a list that contains dictionaries.
You could then easily write that out to a file, use the Pickle module to write
that stuff out to a file, or better yet, use the Shelve module, which I think
is faster and does more stuff.
Thanks.
Jim
-----Original Message-----
From: program-l-bounce@xxxxxxxxxxxxx [mailto:program-l-bounce@xxxxxxxxxxxxx] On
Behalf Of Al Puzzuoli
Sent: Wednesday, October 03, 2012 7:27 AM
To: program-l@xxxxxxxxxxxxx
Subject: [program-l] Re: Some thoughts on objects was ...Re: Re: Python, best
way to return a bunch of data from a function?
Hi Rich,
As always, thanks for yet another very informative response. I am familiar in
theory with object oriented programming, but haven't done it yet in practice.
As I progress in my study of the language, I feel like I'm spending more time
refactoring the little bits of code I've already written to incorporate new
concepts as opposed to adding new functionality to my program. I re-wrote my 6
lists approach to gathering cSV data and am now using the csv.DictReader module
to build a single list of dictionaries. Much easier to manipulate this way. Ah
well, guess that's part of the fun.
Right now, I'm only working with a single stock at a time, and haven't bothered
with devising any sort of storage solution for historical data, just
downloading it as needed on a per session basis, but that too will change soon.
My goal is to get to the point where this thing is actually doing some
meaningful analysis, and then worry about everything else.
Take care,
Al
On 10/2/2012 4:11 PM, R Dinger wrote:
> I think the best way to organize a system is through objects. You may
> not be familiar with object oriented programming, though. I have a
> few thoughts below that explain how I approach such a problem, but
> these are just my quick thoughts.
>
> Think of having a 'stock' class of objects. The class is a template
> for making stocks and has various attributes like a ticker symbol,
> shares owned, some historical data and whatever else you want to
> include in a stock. Note this can grow and evolve over time it does
> not need to be complete in order to start.
>
> Then an instance of a stock object is created for a specific company,
> say BA
> (Boeing) and the historical data is loaded from yahoo or wherever.
> Try thinking of a class as a data type and an object as a variable of that
> type.
> You can then save that specific object in a file, database or
> something else. The class should also include functions to update the
> historical data, compute the average volume and so forth. The
> functions of an object are sometimes called methods.
>
> OO is really just an organizing scheme for the code there is really
> nothing magic about it. Your code is organized around data
> abstractions rather than procedural details. One advantage is that
> problem of computing the average volume is done by simply asking the
> stock to compute it (all the data is right there). The intermediate
> data is not passed all over the place exposing it to inadvertent
> corruption. Most of the stock data is encapsulated in the stock
> objects where it is handy to access.
>
> Next imagine a dialog box for the stock class of objects. The various
> functions of the class are invoked when the various buttons or other
> controls are pushed on the dialog. GUI interfaces go hand and hand
> with OO system design and that notion of encapsulation.
>
> The individual stocks in your system could be organized in a container
> object of some sort with general functions like updating the
> historical data, saving changes and showing current gain or loss. To
> update the container object would loop through the stocks and tell
> each one to update its internal historical data. This could be done
> automatically at startup or via a menu item or whatever.
>
> HTH
>
> Richard
>
> ----- Original Message -----
> From: "Al Puzzuoli" <alpuzz@xxxxxxxxx>
> To: <program-l@xxxxxxxxxxxxx>
> Sent: Monday, October 01, 2012 8:13 PM
> Subject: [program-l] Re: Python, best way to return a bunch of data
> from a function?
>
>
> Hi Rich,
> I guess at this point, I'm still in the hacking around faze. Learning
> the language, and adapting my solution to fit the knowledge I've
> gleaned thus far. So it sounds as if I may not need to take apart my
> CSV? If I don't take it apart, how would I parse it? For example, I
> might want to read the volume column, and calculate its average over the past
> 90 days.
> I'll definitely begin familiarizing myself with the other storage
> alternatives you mentioned.
> Thanks a lot for the assist,
>
> Al
>
> On 10/1/2012 7:50 PM, R Dinger wrote:
>> Using global variables is a bad idea. And answering this question is
>> full of pitfalls, but I will try.
>>
>> I am unclear on why you are taking apart your CSV files in the first
>> place, but if you really want six lists you can simply return them
>> from your "reading-function" as a tuple e.g.:
>> return (list1, list2, ... list6)
>>
>> You can also convert the CSV tuple to a named tuple so you only need
>> one list with named attributes like l.high or l.low. That seems more
>> direct than having six lists.
>>
>> Or you can use a dictionary with the date as the key giving you
>> direct access rather than sequential access.
>>
>> Or you can put the data into a custom designed object and return it.
>>
>> Everything in Python is an object.
>>
>> Or Python comes with the sqlite database and the data could be stored
>> in a suitable DB table.
>>
>> Or Python comes with several other data persistence features like
>> shelves that you could use if you do not like databases.
>>
>> You may change your mind several times as your system evolves. Maybe
>> you should think about how you will be accessing and using this data
>> as that may lead to how to structure it. Object oriented systems are
>> more structured around the data abstractions used than being
>> structured around processing procedures.
>>
>> Keep tinkering and you will eventually get where you want to go.
>>
>> Richard
>> ----- Original Message -----
>> From: "Al Puzzuoli" <alpuzz@xxxxxxxxx>
>> To: <program-l@xxxxxxxxxxxxx>
>> Sent: Monday, October 01, 2012 8:23 AM
>> Subject: [program-l] Python, best way to return a bunch of data from
>> a function?
>>
>>
>> Hi everyone,
>> For my current project, I'm envisioning having a number of different
>> data collection functions. Currently, I'm working with Yahoo. I'm
>> using Urllib to download a CSv file. I then zip the data into
>> appropriate columns, convert it from tuples to lists. Next, I pop
>> the header rows off my lists and convert them to floating point
>> values. Right now, this code is running as part of my main program,
>> but I ultimately want to modularize it and later add data collectors
>> for other sources. So in the case of Yahoo, the above process does
>> the job, but another source might offer the data in JSON format or
>> whatever. Ultimately, how I parse the data should be transparent to
>> the program. The important thing is that the main program gets back 6
>> lists, date, opening, high, low, closing, volume. The most obvious
>> way to do this would seem to be to declare these list as global
>> variables in my data collection functions, but I'm afraid that if I
>> use global variables, I shall incur the wrath of the programming GODS
>> and be afflicted forever after by vengeful gremlins from on high.
>> So is this instance an acceptable use case for global variables? If
>> not, what would be the best way to formulate a function that would
>> do all the necessary parsing and processing, and then return all the
>> data I need in a single pass?
>> Thanks,
>>
>> Al
>>
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