Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From: Terry Reedy <tjreedy@udel.edu>
Newsgroups: comp.lang.python
Subject: Re: Suggestion: make sequence and map interfaces more similar
Date: Thu, 31 Mar 2016 13:41:19 -0400
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On 3/31/2016 10:13 AM, Marko Rauhamaa wrote:

> One could compose a table of correspondences:

with some corrections

>        -------------------------------------------
>        list (L)                    dict (D)
>        -------------------------------------------
>        L[key] = value              D[key] = value
>        del L[key] (*)              del L[key]
>        (*) reassigns all keys
>        key >= 0 and key < len(L)   key in D

'-len(L) <= key < len(L)' or 'key in range(-len(L), len(L)'
Lists, tuples, and ranges have 2 keys for each value,
though that is not guaranteed for sequences in general.

key in D == key in D.keys()

>        range(len(L))               iter(D)

          iter(range(Len(L))          == iter(D.keys())

>        L.clear                     D.clear
>        L.copy                      D.copy
>        lambda key: L[key]          D.get

The purpose of D.get() is to supply a default instead of raising 
KeyError when key not in D. The lambda function above does not do that. 
  Turning subscripting into a function is a side-effect of D.get.  A 
generic get function:

def get(subscriptable, key, default=None):
     try:
         return subscriptable[key]
     except (IndexError, KeyError):
         return default

>        lambda: enumerate(L)        D.items

As I pointed out a couple days ago, an enumerate iterator is quite 
different from a set-like dynamic view.  An actual correspondence:

          enumerate(L)               iter(D.items())

Writing a set-like dynamic view of lists corresponding to D.values() or 
D.items() would be an interesting project.

>        lambda: range(len(L))       D.keys

          iter(range(len(L))          iter(D.keys())
Already given above.  Iterating indexes is now much rarer than iterating 
dict keys.

-- 
Terry Jan Reedy