How to access elemenst in a list of lists?

[Algis Kabaila]

On Tuesday 10 May 2011 17:22:42 Algis Kabaila wrote:
> On Tuesday 10 May 2011 11:25:59 Terry Reedy wrote:
> > On 5/9/2011 8:44 PM, Algis Kabaila wrote:
> > > The method of double indexing in the manner
> > > a[i][j]
> > > for the (i, j) -th element of multi-dimensional array is
> > > well known and widely used. But how to enable the
> > > "standard" matrix notation a[i, j]
> > > in Python 3.2 in the manner of numpy (and other matrix
> > > packages)? Is it subclassing of "special methods"
> > > 
> > > __getitem__() # to get
> > > 
> > > __setitem__()  # to set
> > 
> > Yes.
> > 
> > class listwrap:
> >      def __init__(self, lis):
> >          self._list = lis
> >      
> >      def __getitem__(self, dex):
> >          i,j = dex
> >          return self._list[i][j]
> >      
> >      # __setitem__: exercise for reader
> > 
> > l = listwrap([[1,2,3],['a','b','c']])
> > print(l[0,2],l[1,0])
> > # 3 a
> > 
> > IMO, Hardly worth it for two dimensions.
> 
> Terry,
> 
> Thank you for your response.  I have to confess that I do
> have the cludge of an answer to my own question, but it is a
> cludge; Your method looks much better, though I don't think
> it is complete - this subclassing of __getitem__ appears to
> stop simple list access, i.e. if li = [1, 2 ,3], it seems to
> me that print(li[2])
> would raise an exception, no?
> However,  the method that you have indicated is a neat way to
> solve the problem -- thank you for it!
> 
> OldAl
> 
> PS: just to confirm your method and the limitation of it "as
> is": It is NOT a criticism, just a mere observation,  Good
> method, nice example, great contribution!
> 
> 
> 3 a
> Showing limitation of "as is" in this
> great method for access of list of lists
> Traceback (most recent call last):
>   File "/dat/work/linalg/dim2.py", line 15, in <module>
>     print(ll[1])
>   File "/dat/work/linalg/dim2.py", line 6, in __getitem__
>     i,j = dex
> TypeError: 'int' object is not iterable

Apologies for accidental mail sending before it was completed:
The original code and additional data is as follows 

l = listwrap([[1,2,3],['a','b','c']])
print(l[0,2],l[1,0])
print('''Showing limitation of "as is" in this
great method for access of list of lists''')
ll = listwrap([1,2,3])
print(ll[1])

Above is the output.
Thank you again,

Al.
-- 
Algis
http://akabaila.pcug.org.au/StructuralAnalysis.pdf
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