programming-for-dummies

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Using Sets
✦ When you delete data from a set, the set is just one item smaller.
✦ When you delete data from an array, you’re left with an empty space in
the array.
To remove all data in a set, most programming languages include a command
that clears out an entire set. In Python, the command is clear, such as
clubmembers.clear()
Checking for membership
If you store a bunch of names in an array, how could you verify whether a
specific name is in that array? You’d have to examine each element in the
array and compare it with the name you’re looking for until you either found
a match or reached the end of the array. This typically requires a loop to
examine every array element, one by one.
Sets avoid this problem by making it easy to check whether a chunk of data
is stored in a set. If you had a list of country club members stored in a set, it
might look like this in Python:
from sets import Set
clubmembers = Set([‘Bill Evans’, ‘John Doe’, ‘Mary Jacobs’])
To check whether a name is in a set (a member of that set), use a simple in
command like this:
‘John Doe’ in clubmembers
If this command finds the name John Doe in the set defined by the
clubmembers set, this would return a True value. If this command can’t
find the name John Doe in the clubmembers set, this command would
return a False value.
From the computer’s point of view, it must still exhaustively compare every
name in a set to see whether it matches the name you’re looking for, but
from the programmer’s point of view, you can use a simple in command
rather than write multiple lines of code to examine an array, element by element.
The more work you can make the computer do, the less work you
have to do.
Another way to check for membership is to use the not command with the
in command like this:
‘Hugh Lake’ not in clubmembers