ultra newbie question (don't laugh)

[John Salerno]

Ok, I've decided to make a little project for myself which involves
storing employee information in an XML file. I'm doing this partly to
experiment with working with XML. The blocks in the file will look
something like this:

<researcher id="salerjo01">
<first_name>John</first_name>
<last_name>Salerno</last_name>
<birth_country>United States</birth_country>
<birth_state>Texas</birth_state>
<birth_city>Houston</birth_city>
#etc.......
<researcher>

I also plan to make a GUI frontend with wxPython for entering the
records. This will be fairly easy, but not as fun as writing the logic.
For now I've decided to focus just on writing the logic, and not worry
about the GUI yet.

So this is what I came up with so far, then I sat staring at the screen
wondering how to proceed:

class LabXMLWriter(object):

def write_name(self, first, last, given=''):

Suddenly I realized I just have no idea how to start thinking about what
I need to do. My first instinct was to use a class, as above, but then I
wondered if that was even necessary, since all I need to do is get
information from a user and write it to a file. Do I really need that
information stored in an object?

Then I wondered if I needed an __init__ method, and what could go in it?
Or should I just make separate methods for each bit of information to
write to the file (i.e., name, birth location, address, phone number,
etc.). I thought maybe I could create the ID in the __init__ method
(salerjo01), but to do that I need the name first. I could do this:

def __init__(self, first_name, last_name, given_name=''):
# code to initialize name and create ID

But then I wondered if this detracts from the work that the class
methods would do later.

So you see, what I'm asking for is very basic help, sort of along the
lines of "what things do I need to consider before I even begin this?"
Is OOP necessary here? Would utility functions work just as well for
simply writing the information to a file?

Perhaps I should just take some kind of programming intro class! I read
all these Python books, but when it comes time to write something
non-trivial, I get stuck almost immediately with all the possibilities.

Thanks,
John

 

[Gal Diskin]

Ok, I've decided to make a little project for myself which involves
storing employee information in an XML file. I'm doing this partly to
experiment with working with XML. The blocks in the file will look
something like this:

<researcher id="salerjo01">
<first_name>John</first_name>
<last_name>Salerno</last_name>
<birth_country>United States</birth_country>
<birth_state>Texas</birth_state>
<birth_city>Houston</birth_city>
#etc.......
<researcher>

I also plan to make a GUI frontend with wxPython for entering the
records. This will be fairly easy, but not as fun as writing the logic.
For now I've decided to focus just on writing the logic, and not worry
about the GUI yet.

So this is what I came up with so far, then I sat staring at the screen
wondering how to proceed:

class LabXMLWriter(object):

def write_name(self, first, last, given=''):

Suddenly I realized I just have no idea how to start thinking about what
I need to do. My first instinct was to use a class, as above, but then I
wondered if that was even necessary, since all I need to do is get
information from a user and write it to a file. Do I really need that
information stored in an object?

Then I wondered if I needed an __init__ method, and what could go in it?
Or should I just make separate methods for each bit of information to
write to the file (i.e., name, birth location, address, phone number,
etc.). I thought maybe I could create the ID in the __init__ method
(salerjo01), but to do that I need the name first. I could do this:

def __init__(self, first_name, last_name, given_name=''):
# code to initialize name and create ID

But then I wondered if this detracts from the work that the class
methods would do later.

So you see, what I'm asking for is very basic help, sort of along the
lines of "what things do I need to consider before I even begin this?"
Is OOP necessary here? Would utility functions work just as well for
simply writing the information to a file?

Perhaps I should just take some kind of programming intro class! I read
all these Python books, but when it comes time to write something
non-trivial, I get stuck almost immediately with all the possibilities.

Thanks,
John

I think this is marely a matter of programming style in your case. If
you like to use OOP use it. If not, don't. It doesn't seem to me that
OOP is necessary to anything you just mentioned. Don't let the
possibilities slow you - they're there so you can use whatever you
like, not to flood you with too many options.

Good luck,
Gal

 

[Larry Bates]

Ok, I've decided to make a little project for myself which involves
storing employee information in an XML file. I'm doing this partly to
experiment with working with XML. The blocks in the file will look
something like this:

<researcher id="salerjo01">
<first_name>John</first_name>
<last_name>Salerno</last_name>
<birth_country>United States</birth_country>
<birth_state>Texas</birth_state>
<birth_city>Houston</birth_city>
#etc.......
<researcher>

I also plan to make a GUI frontend with wxPython for entering the
records. This will be fairly easy, but not as fun as writing the logic.
For now I've decided to focus just on writing the logic, and not worry
about the GUI yet.

So this is what I came up with so far, then I sat staring at the screen
wondering how to proceed:

class LabXMLWriter(object):

def write_name(self, first, last, given=''):

Suddenly I realized I just have no idea how to start thinking about what
I need to do. My first instinct was to use a class, as above, but then I
wondered if that was even necessary, since all I need to do is get
information from a user and write it to a file. Do I really need that
information stored in an object?

Then I wondered if I needed an __init__ method, and what could go in it?
Or should I just make separate methods for each bit of information to
write to the file (i.e., name, birth location, address, phone number,
etc.). I thought maybe I could create the ID in the __init__ method
(salerjo01), but to do that I need the name first. I could do this:

def __init__(self, first_name, last_name, given_name=''):
# code to initialize name and create ID

But then I wondered if this detracts from the work that the class
methods would do later.

So you see, what I'm asking for is very basic help, sort of along the
lines of "what things do I need to consider before I even begin this?"
Is OOP necessary here? Would utility functions work just as well for
simply writing the information to a file?

Perhaps I should just take some kind of programming intro class! I read
all these Python books, but when it comes time to write something
non-trivial, I get stuck almost immediately with all the possibilities.

Thanks,
John

On reason to use OOP is to insulate your main code from things like storage
backends or future changes you may decide to make. What if you change your mind
and want to store the data into something other than XML? If you move all your
storage code into an object and have it do the writing/reading then you can
easily replace that object without disrupting your main program. You could even
extend your program and allow someoneto store in CSV, database, or other storage
by adding additional storage objects. I had a project where I was reading data
from CSV file. Later in the implementation the client decided that the file
that was to be processed would be a .ZIP file instead of a plain-text CSV.
Because I had implemented a class to do the reading of all data from the CSV
file that had implemented an iterator, I was able to insert code to open .ZIP
file (using zipfile module), open a file inside the .ZIP and read using CSV
module from the zipped file without ever actually unzipping the file. I didn't
change any top level code and the change took a just a few minutes to implement.
There was little chance of creating unintended problems and I was able to
easily support both the old unzipped CSV filesAND the new zipped files. If I
had not isolated that code into a class, the changes would have been a LOT more
difficult.

It can also be nice to provide for future expansion by supporting additional
keyword arguments. Something like:

def __init__(self, first_name, last_name, **kwargs):

Then process the kwargs for additional fields. This way you can painlessly add
a field to your code by just specifying an additional keyword argument. If the
application is as simple as you describe it may not be worth the additional
effort. Once you have done one of these it will become second nature to think
of creating/using objects in places where you want to provide for maximum
flexibility and code isolation.

At a minimum you should take a look at the elementtree module for handling your
XML. It is downloadable for Python < 2.5 and is part of the standard library
starting with version 2.5.

Hope information helps at least a little.

-Larry Bates

 

[George Sakkis]

So you see, what I'm asking for is very basic help, sort of along the
lines of "what things do I need to consider before I even begin this?"
Is OOP necessary here? Would utility functions work just as well for
simply writing the information to a file?

To start with your last question, yes, they probably would, *IF* all
you need to do is take data from the user (through a GUI, command line,
etc.) and store them in some persistent state (text file, pickle, db,
etc.). In practice, chances are you'll need to do something more with
the data; I mean, what's the point in just storing data without using
them somehow ? Using the data is the core of an application, so the
question you should be able to answer beforehand is "what do I want to
do with all these data?". Compute statistics ? Print reports ? Create a
social network type of app ? All of the above ? You get the point.

After you have some good (or even rough) idea of what you want to do
with the data, the answer to "Is OOP necessary here?" would be
"strictly speaking, no, OOP is never necessary, but it's pretty often a
good idea". I mean, you can code the whole thing in plain old C, with
global functions and variables, and people have been doing this for
ages, but why build a fire from wood when there are zippos? In short,
OOP comes handy when:
a. you want to couple data with behavior (methods), AND
b. you have many instances of the same "kind(s)" around, interacting
with each other (deliberately using "kind" here to avoid starting a
"class" vs "type" theoretical discussion). If there's only one instance
of some "kind", in python it is usually better to have a module instead
of a singleton class (since modules are builtin singletons).

Perhaps I should just take some kind of programming intro class! I read
all these Python books, but when it comes time to write something
non-trivial, I get stuck almost immediately with all the possibilities.

Or, if you're comfortable studying on your own, you could start with a
book or two that focus on software design and architecture, rather than
language details and small programming recipes. I can't think of any
specific title to suggest off the top of my head but I'm sure you'll
get some good suggestions from others if you ask here.

George

 

[Fredrik Lundh]

So you see, what I'm asking for is very basic help, sort of along the
lines of "what things do I need to consider before I even begin this?"
Is OOP necessary here? Would utility functions work just as well for
simply writing the information to a file?

when you get programmers block, telling your brain to "shut up and let
me write some code" is often a good idea. just start tinkering with
your first idea, and see if you can make it work. if you get a little
stuck, hack your way through it. if you get really stuck, take a break,
work on something else for a while, and wait for your brain to come up
with a better idea. repeat.

here's how I would start:

import xml.etree.ElementTree as ET

class Researcher:

# attributes (you can skip this part, if you want)
first_name = None
last_name = None
birth_country = None
birth_state = None
birth_city = None

# the identity is lazily evaluated by getid (see below)
id = None

def getid(self):
if not self.id:
self.id = (self.first_name + self.last_name).lower() # etc
return self.id

def maketree(self):
elem = ET.Element("researcher", id=self.getid())
ET.SubElement(elem, "first_name").text = self.first_name
ET.SubElement(elem, "last_name").text = self.last_name
ET.SubElement(elem, "birth_country").text = self.birth_country
ET.SubElement(elem, "birth_state").text = self.birth_state
ET.SubElement(elem, "birth_city").text = self.birth_city
return elem

x = Researcher()

# simulate the UI's "OK" handler

x.first_name = "John"
x.last_name = "Salerno"
x.birth_country = "United States"
x.birth_state = "Texas"
x.birth_city = "Houston"

print ET.tostring(x.maketree())

</F>

 

[John Salerno]

To start with your last question, yes, they probably would, *IF* all
you need to do is take data from the user (through a GUI, command line,
etc.) and store them in some persistent state (text file, pickle, db,
etc.). In practice, chances are you'll need to do something more with
the data; I mean, what's the point in just storing data without using
them somehow ? Using the data is the core of an application, so the
question you should be able to answer beforehand is "what do I want to
do with all these data?". Compute statistics ? Print reports ? Create a
social network type of app ? All of the above ? You get the point.

Thanks for the advice guys! OOP seems like a good idea, and besides it
can't hurt to experiment with it even if I don't necessarily need it.
I'll give this a shot and maybe post the code later and let you all tear
it apart.

 

[John Salerno]

when you get programmers block, telling your brain to "shut up and let
me write some code" is often a good idea. just start tinkering with
your first idea, and see if you can make it work. if you get a little
stuck, hack your way through it. if you get really stuck, take a break,
work on something else for a while, and wait for your brain to come up
with a better idea. repeat.

Thanks Fredrik! My initial feeling was the opposite, i.e. don't rush
into anything, just stop and think about how I want to do this first.
But then of course the possibilities piled up and I was stuck, so your
suggestion is probably much better at this point. I just need to try
some things! If nothing else, I'll learn what's efficient and what's not.

here's how I would start:
snip

You know, I planned all along to use ElementTree to *read* my XML file,
but like a bonehead I for some reason was trying to create all the
*write* methods myself! Next stop: ElementTree documentation page!

 

[Peter Otten]

Thanks Fredrik! My initial feeling was the opposite, i.e. don't rush
into anything, just stop and think about how I want to do this first.
But then of course the possibilities piled up and I was stuck, so your
suggestion is probably much better at this point. I just need to try
some things! If nothing else, I'll learn what's efficient and what's not.

Here's a lighthearted take on the matter:

http://www.theonion.com/content/node/47469

(link found in a post to python-dev by the notorious Fredrik Lundh)

Peter