Lecture 5

Iteration Tools

• itertools.accumulate(iterable[, func])

• itertools.chain(*iterables)

  my_list = list(chain(['foo', 'bar'], cmd, numbers))

• itertools.chain.from_iterable(iterable)

  list(chain.from_iterable([cmd, numbers]))

• itertools.compress(data, selectors)

letters = 'ABCDEFG'
bools = [True, False, True, True, False]
print(list(compress(letters, bools)))  

• itertools.dropwhile(predicate, iterable)

    def less_than_five(x):
        return x < 5 
    print(list(dropwhile(less_than_five, [1, 4, 5, 1, 6])))
    print(list(dropwhile(lambda x: x > 5, [6, 7, 8, 9, 1, 2, 3, 10])))

• itertools.filterfalse(predicate, iterable)

• itertools.groupby(iterable, key=None)

The key argument is a function, or if none is specified, defaults to the identity function which returns the element unchanged

    from itertools import groupby
    vehicles = [('Ford', 'Taurus'), ('Dodge', 'Durango'),
                ('Chevrolet', 'Cobalt'), ('Ford', 'F150'),
                ('Dodge', 'Charger'), ('Ford', 'GT')]
    sorted_vehicles = sorted(vehicles)
    for key, group in groupby(sorted_vehicles, lambda make: make[0]):
        for make, model in group:
            print('{model} is made by {make}'.format(model=model, make=make))
        print ("**** END OF GROUP ***\n")

• itertools.islice(iterable, start, stop[, step])

• itertools.starmap(function, iterable) ?????????

  The difference between map() and starmap() parallels the distinction between function(a,b) and function(*c).

• Defining functions with *args

• itertools.takewhile(predicate, iterable)

  opposite of the dropwhile iterator

• itertools.tee(iterable, n=2)

• itertools.zip_longest(*iterables, fillvalue=None)

  If the iterables don’t happen to be the same length, then you can also pass in a fillvalue

• itertools.combinations(iterable, r)

• itertools.combinations_with_replacement(iterable, r)

• itertools.product(*iterables, repeat=1)

• itertools.permutations(iterable, r=None)

• Calling functions with *args