On Aug 16, 7:53 pm, beginner <[EMAIL PROTECTED]> wrote:
> On Aug 16, 6:21 pm, James Stroud <[EMAIL PROTECTED]> wrote:
>
>
>
>
>
> > beginner wrote:
> > > Hi All.
>
> > > I'd like to do the following in more succint code:
>
> > > if k in b:
> > > a=b[k]
> > > else:
> > > a={}
> > > b[k]=a
>
> > > a['A']=1
>
> > > In perl it is just one line: $a=$b->{"A"} ||={}.
>
> > I'm afraid you've asked a non sequiter:
>
> > euler 40% cat test.pl
>
> > $a=$b->{"A"} ||={} ;
> > print "$a\n" ;
>
> > $b->{"B"} = 0 ;
> > $a=$b->{"B"} ||={} ;
> > print "$a\n" ;
>
> > $b->{"X"} = 15 ;
> > $a=$b->{"X"} ||={} ;
> > print "$a\n" ;
>
> > euler 41% perl test.pl
> > HASH(0x92662a0)
> > HASH(0x926609c)
> > 15
>
> > James
>
> > --
> > James Stroud
> > UCLA-DOE Institute for Genomics and Proteomics
> > Box 951570
> > Los Angeles, CA 90095
>
> >http://www.jamesstroud.com/
>
> It is not supposed to be used this way.
> $b is supposed to be a hash-table of hash-table. If a key exists in
> $b, it points to another hash table. The $a=$b->{"A"} ||={} pattern is
> useful when you want to add records to the double hash table.
>
> For example, if you have a series of records in the format of (K1, K2,
> V), and you want to add them to the double hash-table, you can do
> $a=$b->{K1} || ={}
> $a->{K2}=V- Hide quoted text -
>
> - Show quoted text -
I think this demonstrates the Python version of what you describe.
-- Paul
from collections import defaultdict
data = [
('A','B',1), ('A','C',2), ('A','D',3), ('B','A',4),
('B','B',5), ('B','C',6), ('B','D',7),
]
def defaultdictFactory():
return defaultdict(dict)
table = defaultdict(defaultdictFactory)
for k1,k2,v in data:
table[k1][k2] = v
for kk in sorted(table.keys()):
print "-",kk
for jj in sorted(table[kk].keys()):
print " -",jj,table[kk][jj]
prints:
- A
- B 1
- C 2
- D 3
- B
- A 4
- B 5
- C 6
- D 7
--
http://mail.python.org/mailman/listinfo/python-list
