help with my first use of a class

[James Stroud]

BartlebyScrivener wrote:
> I am a mere hobbyist. Spent several hours trying to make a class,
> because I think this is an occasion where I need one. But I can't make
> it work.
> 
> This code "works" (only because of the global c, which I know I'm
> supposed to avoid, by using a Class). I edited the rest to leave out
> the irrelevant formatting and printing of the quotations.
> 
> I've read about Classes several times, but I don't "get" them yet.
> Obviously. If I can solve one real life problem like this, then maybe
> I'll see the light.
> 
> If I understand the power of Classes correctly, I could make one that
> would allow me to make a new instance that would connect to, say, an
> SQLite3 db instead of the Access db, as well as to create more methods
> that will do different SQL searches.
> 
> Thank you for any help,
> 
> rd
> 
> --------------------------------------
> 
> import mx.ODBC.Windows as odbc
> import sys
> import random
> 
> def connect():
>     global c
>     db='DSN=Quotations'
>     conn = odbc.DriverConnect(db)
>     c = conn.cursor()
> 
> def random_quote():
>     """
>     Counts all of the quotes in MS Access database Quotations2005.mdb.
>     Picks one quote at random and displays it using textwrap.
>     """
>     c.execute ("SELECT COUNT(Quote) FROM PythonQuoteQuery")
>     # Yields the number of rows with something in the quote field
>     total_quotes = c.fetchone()
>     # Get a random number somewhere between 1 and the number of total
> quotes
>     quote_number = (random.randint(1, total_quotes[0]),)
>     # Select a quote where the ID matches that number
>     c.execute ("SELECT Author, Quote FROM PythonQuoteQuery WHERE ID=?",
> quote_number)
>     quote = c.fetchone()
>     blah blah blah
> 
> def print_quote()
>     code to format and print the quote (which will also have to be
> global, unless I learn Classes!)
> 
> 
> if __name__ == '__main__':
>     if len(sys.argv) == 1:
>         connect()
>         random_quote()
>         print_quote()
> 

You really don't need classes for this, just parameters + return values. 
Probably best would be to master the idea of parameters + return values 
before yo move on to classes. This is called "procedural" programming. 
Notice that there is no name collision because of strict python 
namespaces (a good idea, according to Tim Peters).


For example:

def connect():
     db='DSN=Quotations'
     conn = odbc.DriverConnect(db)
     c = conn.cursor()
     # NOTE THE RETURN VALUE:
     return c

def random_quote(c):  # <== NOTE THE PARAMETER
     """
     Counts all of the quotes in MS Access database Quotations2005.mdb.
     Picks one quote at random and displays it using textwrap.
     """
     c.execute ("SELECT COUNT(Quote) FROM PythonQuoteQuery")
     # Yields the number of rows with something in the quote field
     total_quotes = c.fetchone()
     # Get a random number somewhere between 1 and ...
     quote_number = (random.randint(1, total_quotes[0]),)
     # Select a quote where the ID matches that number
     q = "SELECT Author, Quote FROM PythonQuoteQuery WHERE ID=?"
     c.execute (q, quote_number)
     quote = c.fetchone()
     # NOTE THE RETURN VALUE:
     return quote

def print_quote(quote): # <== NOTE THE PARAMETER
   print quote           # <== WHATEVER YOU WANT TO DO

if __name__ == '__main__':
     if len(sys.argv) == 1:
         c = connect()            # <== NO COLLISION: NAMESPACES
         quote = random_quote(c)  # <== DITTO
         print_quote(quote)       # THERE YOU HAVE IT


James