[Tutor] Good Taste Question: Using SQLite3 in Python

[Jugurtha Hadjar]

On 04/29/2015 09:06 AM, Alan Gauld wrote:
> In principle its an acceptable strategy. A close alternative
> would be to name the queries as explicit class variables.
> So for example you would use:
>
> cur.execute(self.find_phone_query,(....))
>
> Its less typing and less error prone in that you get a
> syntax error on mistyping rather than a run time exception.
>

That's what I had initially but I used dictionaries for regexes I match 
the messages against to determine the type, I thought I'd organize stuff 
of the same nature together in a dictionary.
	
	JUNK = 'JUNK'

	RE_TYPE = {
		'TYPE1'  : re.compile(r'xxx'),
		'TYPE2'  : re.compile(r'yyy'),
		  ...
		'TYPEn'  : re.compile(r'aaa'),
	}

Then to get the type of the message, I just have to do:

	gen = (k for k in self.RE_TYPE if RE_TYPE[k].findall(msg_text))
	msg_type = next(gen, self.JUNK)


>> - Methods closed the connection themselves, so I used `with` in
>> `init_db` instead of `try`, as it would close the connection
>> automatically and rollback (I hope I'm not making this up).
>
> Try/except and with do different things but in this case
> you can get away with it. The only loss is that your errors
> here are not formatted in the same way as the other messages.

I wrote it to do one specific job that's to be followed by some other 
task that _would_ raise an exception.

Maybe it's lazy and am relying on the methods that call `init_db` to 
deal with the error. `init_db` just returns a connection and a cursor.. 
If the file didn't exist, it'd be created but without schema, the 
calling method (like `create` or `find` _will_, however produce an error 
as it tries to read/write.


> Consider using docstrings rather than comments to describe the method
> I see you do that below...

Roger that.

>>          (__, cursor) = self.init_db()
>
> Don't use the __ 'variable' here, be explicit, it makes
> maintenance much easier.
>

I actually searched specifically for something like this. In MATLAB, 
there's the ~ that does this. I'm not trying to write Python in a MATLAB 
style, but I was glad I found it here:

http://docs.python-guide.org/en/latest/writing/style/#create-an-ignored-variable

I was only interested in the cursor in that method. `init_db` returned 
only a connection in the beginning, but I didn't want to write 
conn.cursor every time.


>>          try:
>>              cursor.execute(
>>                  self.QUERIES['FIND_PHONE'],
>>                  (self.phone,)
>>              )
>>              found = cursor.fetchone()
>>              return True if found else False
>>          except Exception as e:
>>              return self.ERROR.format(e.args[0])
>
> Don't catch Exception, it's too wide. Catch the
> actual errors that might arise, be as specific as possible.

Thanks for bringing that to my attention.

>
>>      def create(self, seed_balance):
>>          ''' Create a database entry for the sender.'''
>>
>>          conn, cursor = self.init_db()
>>          try:
>>              cursor.execute(
>>                  self.QUERIES['CREATE'],
>>                  (self.phone, seed_balance)
>>              )
>>              conn.commit()
>>          except Exception as e:
>>              return self.ERROR.format(e.args[0])
>
>
> as above
>
>

Thank you for the feedback, Alan.


-- 
~Jugurtha Hadjar,