[Tutor] implementing set operations [was Re: (no subject)]

[wesley chun]

> could this be done in a more elegant fashion?

in addition to alan's obvious solution, if you wanted to roll your
own, you have a good start. my comments below.


> def Unite(set1, set2):          # evaluate 2 lists, join both into 1 new list
>        newList = []
>        for item in set1:
>                newList.append(item)
>        for item in set2:
>                newList.append(item)
>        newList.sort()
>        return newList

- as a style point, use lowercase for all function and variable names.
Capping the first letter is recommended only for class names.

- changing it from "unite" to "union" would make it slightly more accurate

- why the sort()? sets, are by default, unordered data structures...
think  of drawing its elements inside the circles in Venn diagrams.

- if you do end up using Python sets, use the set() factory function
in 2.x, i.e, newSet = set(set1) + set(set2); or set literals in Python
3.x, i.e., mySet = {1, 5, -4, 42}, if you have the exact elements


> def Intersect(set1, set2):              # evaluate 2 lists, check for
> commonalities, output commonalities to 1 new list
>        newList = []
>        for item in set1:
>                if item in set1 and item in set2:
>                        newList.append(item)
>        newList.sort()
>        return newList

- the "item in set1 and " in the if-statement is redundant. blow it away

- i think you can build it using a listcomp


> def Negate(set1, set2):         # evaluate 2 lists, return negation of 1st list
>        newList = []
>        for item in set1:
>                if item in set2:
>                        set1.remove(item)
>        newList = set1
>        return newList

- you probably don't want to call set1.remove(). lists are immutable,
and you would've change the contents of set1. it's best if you made
newList a copy of set1, i.e., newList = list(set1) or newList =
set1[:], and *then* did your for-loop

- better yet, use a list comp with an if to build newList to avoid all
of the shenanigans i just described

hope this helps!
-- wesley
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
"Core Python Programming", Prentice Hall, (c)2007,2001
"Python Fundamentals", Prentice Hall, (c)2009
    http://corepython.com

wesley.j.chun :: wescpy-at-gmail.com
python training and technical consulting
cyberweb.consulting : silicon valley, ca
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