Python Intro - #2 - Tuples

tuplesalsocool.py

# Welcome back for Jeff's second 5 minute intro to Python.
 
# This time we'll talk about the list's immutable cousin, the tuple.
 
from collections import namedtuple

def main():
    # tuples can be considered as immutable lists.  A lot of what
    # I'm going to show you here can also be done with lists, but
    # it seems to fit better here.
    name = ("John", "Q", "Public")
    
    # A common misconception is that parenthesis are what specify
    # a tuple, but it's actually the comma.  That's why a 1-tuple
    # looks like this:
    firstonly = ("John", )
    assert len(firstonly) == 1   # even though it looks like it should be two
    
    # You can assign a tuple to multiple variables
    first, middle, last = name
    print "{2}, {0} {1}.".format(first, middle, last)
    
    # You can use the tuple in place of all three variables as well,
    # though you have to put a * in there.
    print "{2}, {0} {1}.".format( *name )
    
    # because you can assign a tuple to multiple variables, and you don't
    # need the parens to define a tuple, you end up with this well worn
    # chestnut for swapping two variables
    a, b = "first", "second"
    a, b = b, a
    print a, b
    
    # or more interesting
    a, b = 0, 1
    for _ in xrange(20):
        print a
        a, b = b, a+b
        
    print "Fibiotastic!"
    
    # xrange(20) returns an iterator that runs 0..19.  range(20) would
    # actually return the list [0, 1, 2, ... , 18, 19], which is suboptimal
    # for large numbers, so just get used to xrange().   Also, the _ here
    # is just a dummy value, since we don't plan to use the iterated value.
    
    #-----------
    
    # Python's object model is ok, but a bit weak.  You can do most of the
    # typical things but, in particular if the object is just to store data,
    # the language and libraries give you other options.   Lists are one,
    # and you'll often see people just storing data in a list and working
    # with it as an array.   But there's a nice solution with 'namedtuple'.

    FullName = namedtuple( 'FullName', 'first, middle, last' )
    
    name = FullName( "John", "Q", "Public" )
    print name.first
    print name.middle
    print name.last
    

if __name__ == "__main__":
    # this is a common idiom.  By default python will just start
    # at the top and run, but coming from a C background, you
    # might be expecting a main() function.  This checks to see
    # if the program is being run stand-alone (__name__ == "__main__")
    # and executes main().  If it were imported as a module in another
    # application, then main() wouldn't run.   This is useful for 
    # setting up unit tests, etc.
    main()