EP 17 Be Defensive When Iterating Over Arguments ref: http://qiita.com/giwa/items/3c386c906472c7d54f24

file0.txt

def normalize(numbers):
    total = sum(numbers)
    result = []
    for value in numbers:
        percent = 100 * value / total
        result.append(percent)

    return result

file1.txt

>>> visits = [15, 35, 80]
>>> percentage = normalize(visits)
>>> percentage
[11.538461538461538, 26.923076923076923, 61.53846153846154]

file2.txt

def read_visits(data_path):
    with open(data_path) as f:
        for line in f:
            yield int(line)

file3.txt

>>> it = read_visits('data')
>>> percentage = normalize(it)
>>> percentage
[]

file4.txt

it = read_visits('data')
list(it)
[15, 35, 80]
list(it)
[]

file5.txt

def normalize(numbers):
    numbers = list(numbers) # Copy the iterator
    total = sum(numbers)
    result = []
    for value in numbers:
        percent = 100 * value / total
        result.append(percent)

    return result

file6.txt

def normalize_func(get_iter):
    total = sum(get_iter()) # New Iterator
    result = []
    for value in get_iter(): # New Iterator
        percent = 100 * value / total
        result.append(percent)

    return result

file7.txt

precentage = normalize_func(lambda: read_visits(path))

file8.txt

class ReadVisits:
    def __init__(self, data_path):
        self.data_path = data_path

    def __iter__(self):
        with open(self.data_path) as f:
            for line in f:
                yield int(line)

file9.txt

def normalize(numbers):
    if iter(numbers) is iter(numbers):
        raise TypeError("Must supply a container")
    total = sum(numbers)
    result = []
    for value in numbers:
        percent = 100 * value / total
        result.append(percent)

    return result