Step further with filebasedMessages

[Cecil Westerhof]

Op Tuesday 5 May 2015 13:08 CEST schreef Peter Otten:

> Cecil Westerhof wrote:
>
>> I now defined get_message_slice:
>> ### Add step
>> def get_message_slice(message_filename, start, end):
>
> Intervals are usually half-open in Python. I recommend that you
> follow that convention.

I will change it.


>> """
>> Get a slice of messages, where 0 is the first message
>> Works with negative indexes
>> The values can be ascending and descending
>> """
>>
>> message_list    = []
>> real_file       = expanduser(message_filename)
>> nr_of_messages  = get_nr_of_messages(real_file)
>> if start < 0:
>> start += nr_of_messages
>> if end < 0:
>> end += nr_of_messages
>> assert (start >= 0) and (start < nr_of_messages)
>
> You should raise an exception. While asserts are rarely switched off
> in Python you still have to be prepeared, and an IndexError would be
> a better fit anyway.

OK.


> Should you later decide that a database is a better fit you can
> change read_messages() to return a class that transparently accesses
> that database. Again, most of the work is already done:
>
> class Messages(collections.Sequence):
> def __init__(self, filename):
> self.filename = filename)
> def __getitem__(self, index):
> # read record(s) from db
> def __len__(self): 
> # return num-records in db
>
> def read_messages(filename):
> return Messages(filename)

Another thing I have to look into. :-D


> By the way, where do you plan to use your functions? And where do
> the indices you feed them come from?

In my case from:
    get_random_message
and:
    dequeue_message

Both also in:
    https://github.com/CecilWesterhof/PythonLibrary/blob/master/filebasedMessages.py

I should write some documentation with those functions. ;-)


I have a file with quotes and a file with tips. I want to place random
messages from those two (without them being repeated to soon) on my
Twitter page. This I do with ‘get_random_message’. I also want to put
the first message of another file and remove it from the file. For
this I use ‘dequeue_message’.

-- 
Cecil Westerhof
Senior Software Engineer
LinkedIn: http://www.linkedin.com/in/cecilwesterhof