Home Original page

syntax philosophy

Dave Benjamin ramen at lackingtalent.com
Tue Nov 18 16:49:26 EST 2003 
In article <hvjub.4572$sb4.1007 at newsread2.news.pas.earthlink.net>, Andrew Dalke wrote:
> Similarly, dictionaries require that entries be created before they
> can be used.  This is because it's impossible for Python to
> know which value you want for the default.  Python is strongly
> typed, so "2"+1 will raise an exception, unlike Perl where it
> yields the number 3.  If Python used a 0 for the default then
> what if you really wanted to concatenate strings?  If it used
> "" then what if you wanted to add numbers?  Whatever choice
> you make, it will be wrong for most cases.

I agree with everything else you said here, but want to caution against your
claim that it's "impossible for Python to know" what to supply as a default.
For instance--and I'm not saying this is better or worse, nor that it is in
harmony with the Python Way--Ruby works like this instead:

irb(main):001:0> d = {}
=> {}
irb(main):002:0> d['a']
=> nil
irb(main):003:0> d.default = 0
=> 0
irb(main):004:0> d['a']
=> 0
irb(main):005:0> d.fetch('a')
IndexError: key not found
        from (irb):5:in fetch'
        from (irb):5

So, as you can see, the default behavior in Ruby is akin to Python's
dict.get (which allows you to supply a default), and the exception-throwing
method is "fetch", instead of [].

In summary:

  Python           Ruby
  -------------    ----------------------
  d['a']           d.fetch('a')
  d.get('a')       d['a']
  d.get('a', 0)    d.default = 0;  d['a']

I prefer the Python way because the lazier syntax ([]) is fail-fast.

-- 
.:[ dave benjamin (ramenboy) -:- www.ramenfest.com -:- www.3dex.com ]:.
: d r i n k i n g   l i f e   o u t   o f   t h e   c o n t a i n e r :
More information about the Python-list mailing list