Array of dict or lists or ....?

[Pat]

I can't figure out how to set up a Python data structure to read in data
that looks something like this (albeit somewhat simplified and contrived):
States
Counties
Schools
Classes
Max Allowed Students
Current enrolled Students

Nebraska, Wabash, Newville, Math, 20, 0
Nebraska, Wabash, Newville, Gym, 400, 0
Nebraska, Tingo, Newfille, Gym, 400, 0
Ohio, Dinger, OldSchool, English, 10, 0

With each line I read in, I would create a hash entry and increment the
number of enrolled students.

I wrote a routine in Perl using arrays of hash tables (but the syntax
was a bear) that allowed me to read in the data and with those arrays of
hash tables to arrays of hash tables almost everything was dynamically
assigned.

I was able to fill in the hash tables and determine if any school class
(e.g. Gym) had exceeded the number of max students or if no students had
enrolled.

No, this is not a classroom project. I really need this for my job.
I'm converting my Perl program to Python and this portion has me stumped.

The reason why I'm converting a perfectly working program is because no
one else knows Perl or Python either (but I believe that someone new
would learn Python quicker than Perl) and the Perl program has become
huge and is continuously growing.

[George Sakkis]

On Oct 7, 10:15 pm, Pat <[e-mail] rote:

Dennis Lee Bieber wrote:

On Mon, 06 Oct 2008 19:45:07 -0400, Pat <[e-mail] eclaimed the
following in comp.lang.pytho n:

I can't figure out how to set up a Python data structure to read in data
that looks something like this (albeit somewhat simplified and contrived):

States
Counties
Schools
Classes
Max Allowed Students
Current enrolled Students

Nebraska, Wabash, Newville, Math, 20, 0
Nebraska, Wabash, Newville, Gym, 400, 0
Nebraska, Tingo, Newfille, Gym, 400, 0
Ohio, Dinger, OldSchool, English, 10, 0

<snip>

The structure looks more suited to a database -- maybe SQLite since
the interface is supplied with the newer versions of Python (and
available for older versions).

Seconded.

I don't understand why I need a database when it should just be
a matter of defining the data structure.

Picking an appropriate data structure depends on the kind of
functionality you want to provide. So far you basically described just
one requirement: keep a tally of how many students are in each class
and compare it to the max allowed (and zero). If that's the only kind
of query you want to run against your data, there's no reason to index
separately each state, county, or school; all you care about are
classes. A simple data structure that satisfies perfectly the
requirement could then be:

# mapping of {class-info : (max,enrolled)}

data = {
('Nebraska', 'Wabash', 'Newville', 'Math') : (20, 0),
('Nebraska', 'Wabash', 'Newville', 'Gym') : (400, 0),
('Nebraska', 'Tingo', 'Newville', 'Gym') : (400, 0),
('Ohio', 'Dinger', 'OldSchool', 'English') : (10, 0),
}

Of course this data structure is pretty bad at answering a query like
"how many classes are there in Nebraska" or "what's the average number
of enrolled students in Newville". The more general information you
might want to get from the data, the more obvious it becomes that you
need a real database.

HTH,
George

[Ben Finney]

George Sakkis <ge***********@ gmail.comwrites :

On Oct 7, 10:15 pm, Pat <[e-mail] rote:

I don't understand why I need a database when it should just be a
matter of defining the data structure.

Picking an appropriate data structure depends on the kind of
functionality you want to provide.

[…]

The more general information you might want to get from the data,
the more obvious it becomes that you need a real database.

Thanks very much for posting this answer; I tried to do something
similar but couldn't get at the essential points the way you did here.

Perhaps the original poster is confusing “you should use a database�
with “you should use a database stored in a fully-concurrent
dedicated database management system�.

Far from it: with Python 2.5 you have SQLite (in the ‘sqlite3’
module), which would be ideal for implementing a powerful relational
SQL database used directly by one program instance, without needing a
full-blown database management system in a separately-administrated
server application.

--
\ “Patience, n. A minor form of despair, disguised as a virtue.� |
`\ —Ambrose Bierce, _The Devil's Dictionary_, 1906 |
_o__) |
Ben Finney

[Gabriel Genellina]

En Tue, 07 Oct 2008 23:15:54 -0300, Pat <Pa*@junk.netes cribió:

Dennis Lee Bieber wrote:

>On Mon, 06 Oct 2008 19:45:07 -0400, Pat <Pa*@junk.comde claimed the
following in comp.lang.pytho n:

>>I can't figure out how to set up a Python data structure to read in
data that looks something like this (albeit somewhat simplified and
contrived):
States
Counties
Schools
Classes
Max Allowed Students
Current enrolled Students

Nebraska, Wabash, Newville, Math, 20, 0
Nebraska, Wabash, Newville, Gym, 400, 0
Nebraska, Tingo, Newfille, Gym, 400, 0
Ohio, Dinger, OldSchool, English, 10, 0

<snip>

>The structure looks more suited to a database -- maybe SQLite since
the interface is supplied with the newer versions of Python (and
available for older versions).

I don't understand why I need a database when it should just be a matter
of defining the data structure. I used a fictional example to make it
easier to (hopefully) convey how the data is laid out.

You don't need a full-blown-multiuser-concurrent-petabyte-capable-server
database, just one that does the job. SQLite is very small and comes with
Python 2.5

The Perl routine works fine and I'd like to emulate that behavior but
since I've just starting learning Python I don't know the syntax for
designing the data structure. I would really appreciate it if someone
could point me in the right direction.

So none of the previously posted alternatives worked for you?

--
Gabriel Genellina

[Scott David Daniels]

Pat wrote:

I can't figure out how to set up a Python data structure to read in data
that looks something like this (albeit somewhat simplified and contrived):

States
Counties
Schools
Classes
Max Allowed Students
Current enrolled Students

Nebraska, Wabash, Newville, Math, 20, 0
Nebraska, Wabash, Newville, Gym, 400, 0
Nebraska, Tingo, Newfille, Gym, 400, 0
Ohio, Dinger, OldSchool, English, 10, 0

With each line I read in, I would create a hash entry and increment the
number of enrolled students.

You might want something like this:

>>import collections, functools
int_dict = functools.parti al(collections. defaultdict, int)
curr = functools.parti al(collections. defaultdict, int)
# builds a dict-maker where t = curr(); t['name'] += 1 "works"
for depth in range(4):

# add a layer with a default of the preceding "type"
curr = functools.parti al(collections. defaultdict, curr)

>>base = curr() # actually make one
base['Nebraska']['Wabash']['Newville']['Math']['max'] = 20
base['Nebraska']['Wabash']['Newville']['Math']['curr'] += 1
base['Nebraska']['Wabash']['Newville']['Math']['curr']

1

>>base['Nebraska']['Wabash']['Newville']['English']['curr']

0
--Scott David Daniels
Sc***********@A cm.Org