reduction

[Steven D'Aprano]

On Wed, 1 Jun 2016 12:22 am, Fillmore wrote:

> 
> My problem. I have lists of substrings associated to values:
> 
> ['a','b','c','g'] => 1
> ['a','b','c','h'] => 1
> ['a','b','c','i'] => 1
> ['a','b','c','j'] => 1
> ['a','b','c','k'] => 1
> ['a','b','c','l'] => 0  # <- Black sheep!!!
> ['a','b','c','m'] => 1
> ['a','b','c','n'] => 1
> ['a','b','c','o'] => 1
> ['a','b','c','p'] => 1

Are the first three items always the same? If so, they're pointless, and get
rid of them.

'g' => 1
'h' => 1
'i' => 1
...

is best stored as a dict.


If not, well, does 'l' *always* represent 0? In other words:

['a','b','c','l'] => 0
['a','b','d','l'] => 0
['x','y','z','l'] => 0
...

then it sounds like you need a dict storing each letter individually:

d = {'a': 1, 'b': 1, 'c': 1, 'l': 0}

for letter in ['a','b','c','l']:
    if d[letter] == 0:
        print("Black sheep")
        break


which can be written more compactly as:

if not all(d[letter] for letter in 'abcl'):
    print("Black sheep")


If your items actually are letters, then you can reduce the fiddly typing
with something a bit easier:


# instead of 
# d = {'a': 1, 'b': 1, 'c': 1, 'l': 0}

letters = 'abcdefghijklmno'
bits =    '111111111110111'
d = {k: int(b) for k, b in zip(letters, bits)}



-- 
Steven