Hi folks,
Coming from a language background that has a different approach to variables
(*cough* Java *cough*), I'm trying to understand Python's typing conventions
and how to deal with unknown variable types in my code. And as a newbie, I'm
really concerned with not writing code that will make the actual Python
programmer who will be maintaining my code jump out the window from
frustration.
An example: I have a directory tree containing year directories (in the form
YYYY, ie, "2011"), which contain month directories (in the form MM, ie,
"05"), which in turn contain files. I'm writing a Python function to iterate
over the tree & return a list of the file names from either the full tree
(args==None) or a specified time period within that - ie, Feb. '10 to May
'11 (args==startdate, enddate). I'm not sure what the most pythonic approach
to dealing with the variables here would be. I have several options:
- accept datetime objects and then get the year/month info from that
- accept a string (and maybe check its length, add "20" if it's two
digits, or reject it if it's more than 4)
- accept an integer (and maybe check that it's reasonable)
My first inclination would be to only accept 4-digit year and 2-digit month
integers and fail the rest, but I understand the value of dealing with
different input types here. My second guess would be to use isinstance() for
each possibility, since different things need to happen in each case. The
"pythonic" approach, as best as I can gather, would be a try/catch block and
use the exception types to do the different processing. However, for
example, both trying to get a year from a string and a len() of an int raise
a TypeError, and in general I'm not sure how to approach this - or am I
overthinking things?
Finally, I'm aware that I'm really bringing up two topics here:
1) What is the best approach in this and similar cases, in terms of actual,
working code that won't make the next user of this code cry? How do/should I
distinguish error types in this case?, and less importantly,
2) Can anyone help me get a good handle on the philosophical issues here?
I've read several discussions (both strongly against
type-checking<http://www.canonical.org/%7Ekragen/isinstance/>and more
lenient<http://dobesland.wordpress.com/2007/10/07/python-isinstance-considered-useful/>,
as well as good general
explanations<http://www.voidspace.org.uk/python/articles/duck_typing.shtml>),
but some of it's over my head, a lot of it says something like "I suggest we
change Python so it does X", and I'm not sure what it all means for me and
my little filename-grabbing script. It's all just a bunch of quaking to me
right now ...
Thanks so much,
Cory
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