1. Iterables, Sequences, and Iterators

Iterables

Iterable is an object that can be looped over. It represents a collection of elements that can be accessed one by one.

We can use the following function to test if an object is an iterable:

def is_iterable(param):
    try:
        iter(param)
        return True
    except TypeError:
        return False

Let's save some objects in a dictionary and test them:

python_objects = {
    "Integer": 1,
    "Float": 1.2,
    "Boolean": True,
    "Complex": 1 + 2j,
    "String": "Hello",
    "List": [1, 2, 3],
    "Tuple": (1, 2, 3),
    "Set": {1, 2, 3},
    "Dictionary": {"a": 1, "b": 2, "c": 3},
    "None": None,
    "Range": range(10),
    "Generator": (i for i in range(10)),
    "Function": is_iterable,
    "Lambda": lambda x: x**2,
}

for name, obj in python_objects.items():
    print(f"{name:12}: {is_iterable(obj)}")

We get the following output and detect the iterable object:

Integer     : False
Float       : False
Boolean     : False
Complex     : False
String      : True
List        : True
Tuple       : True
Set         : True
Dictionary  : True
None        : False
Range       : True
Generator   : True
Function    : False
Lambda      : False

Sequences

Sequence is a subtype of iterables. It is an ordered collection of elements that can be indexed by numbers.

Let's take a look at to the most common iterables and check them if they are a sequence or not:

python_iterables = {
    "String": "Hello",
    "List": [1, 2, 3],
    "Tuple": (1, 2, 3),
    "Set": {1, 2, 3},
    "Dictionary": {"a": 1, "b": 2, "c": 3},
}

def is_sequence(param):
    try:
        param[0]
        return True
    except:
        return False

We get the following output:

String      : True
List        : True
Tuple       : True
Set         : False
Dictionary  : False

Iterators

Iterator is an object that produces items from its associated iterable. Iterator protocol consists of two methods namely, __iter__ and __next__.

class AnIteratorClass:
    def __init__(self):
        self.a = 1

    def __iter__(self):
        return self

    def __next__(self):
        if self.a <= 5:
            x = self.a
            self.a += 1
            return x
        else:
            raise StopIteration

Now we can use the following test:

def is_iterator(param):
    try:
        next(param)
        return True
    except TypeError:
        return False

Also a very simple way to create iterators is to use generators:

def generator_function():
    for i in range(10):
        yield i

Result

As a conclusion we can summarize the status of the Python objects that we will use in this course as given below:

Name	Iterable	Iterator	Sequence
Integer	False	False	False
Float	False	False	False
Boolean	False	False	False
Complex	False	False	False
String	True	False	True
List	True	False	True
Tuple	True	False	True
Set	True	False	False
Dictionary	True	False	False
None	False	False	False
Range	True	False	True
Generator	True	True	False
Function	False	False	False
Lambda	False	False	False