Data structure for maintaining tabular data in memory?

Question

My scenario is as follows: I have a table of data (handful of fields, less than a hundred rows) that I use extensively in my program. I also need this data to be persistent,

Answer 1

I personally wrote a lib for pretty much that quite recently, it is called BD_XML

as its most fundamental reason of existence is to serve as a way to send data back and forth between XML files and SQL databases.

It is written in Spanish (if that matters in a programming language) but it is very simple.

from BD_XML import Tabla

It defines an object called Tabla (Table), it can be created with a name for identification an a pre-created connection object of a pep-246 compatible database interface.

Table = Tabla('Animals') 

Then you need to add columns with the agregar_columna (add_column) method, with can take various key word arguments:

• campo (field): the name of the field

• tipo (type): the type of data stored, can be a things like 'varchar' and 'double' or name of python objects if you aren't interested in exporting to a data base latter.

• defecto (default): set a default value for the column if there is none when you add a row

• there are other 3 but are only there for database tings and not actually functional

like:

Table.agregar_columna(campo='Name', tipo='str')
Table.agregar_columna(campo='Year', tipo='date')
#declaring it date, time, datetime or timestamp is important for being able to store it as a time object and not only as a number, But you can always put it as a int if you don't care for dates
Table.agregar_columna(campo='Priority', tipo='int')

Then you add the rows with the += operator (or + if you want to create a copy with an extra row)

Table += ('Cat', date(1998,1,1), 1)
Table += {'Year':date(1998,1,1), 'Priority':2, Name:'Fish'}
#…
#The condition for adding is that is a container accessible with either the column name or the position of the column in the table

Then you can generate XML and write it to a file with exportar_XML (export_XML) and escribir_XML (write_XML):

file = os.path.abspath(os.path.join(os.path.dirname(__file__), 'Animals.xml'))
Table.exportar_xml()
Table.escribir_xml(file)

And then import it back with importar_XML (import_XML) with the file name and indication that you are using a file and not an string literal:

Table.importar_xml(file, tipo='archivo')
#archivo means file

Advanced

This are ways you can use a Tabla object in a SQL manner.

#UPDATE  SET Name = CONCAT(Name,' ',Priority), Priority = NULL WHERE id = 2
for row in Table:
    if row['id'] == 2:
        row['Name'] += ' ' + row['Priority']
        row['Priority'] = None
print(Table)

#DELETE FROM  WHERE MOD(id,2) = 0 LIMIT 1
n = 0
nmax = 1
for row in Table:
    if row['id'] % 2 == 0:
        del Table[row]
        n += 1
        if n >= nmax: break
print(Table)
this examples assume a column named 'id'
but can be replaced width row.pos for your example.
if row.pos == 2:
The file can be download from:
https://bitbucket.org/WolfangT/librerias

                                                        

              
                
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