Advanced Collections in Python

There are four different types of collections in Python:

The list() constructor returns a list in Python.

Example: Create a list from an iterator object

# objects of this class are iterators
class PowerTwo:
    def __init__(self, max):
        self.max = max

    def __iter__(self):
        self.num = 2
        return self

    def __next__(self):
        if (self.num >= self.max):
            raise StopIteration
        result = 2 ** self.num
        self.num += 1
        return result


pow_two = PowerTwo(9)
pow_two_iter = iter(pow_two)

print(list(pow_two_iter))

Output:

[4, 8, 16, 32, 64, 128, 256]

Process finished with exit code 0

We have to use "import collections" function to call these ones.

namedTuple

Python includes a container-like dictionaries function called "namedtuple()" in the "collections" package. They, like dictionaries, include keys that are hashed to a certain value. On the contrary, it provides both key-value and iteration access, whereas dictionaries do not.

# Python code to demonstrate namedtuple()

from collections import namedtuple

# Declaring namedtuple()
Employee = namedtuple('Employee', ['name', 'age', 'DOB'])

# Adding values
S = Employee('Jack', '23', '2541997')

# Access using index
print("The Employee age using index is : ", end="")
print(S[1])

# Access using name
print("The Employee  name using keyname is : ", end="")
print(S.name)

Output:

The Employee age using index is : 23
The Employee name using keyname is : Jack

Process finished with exit code 0

OrderedDict

An OrderedDict is a subclass of dictionary that remembers the order in which keys were initially placed. The sole distinction between dict() and OrderedDict() is:

Example:

# A Python program to demonstrate working of OrderedDict
from collections import OrderedDict
d = {}
for key, value in d.items():
    print(key, value)

print("\nThis is an Ordered Dict:\n")
od = OrderedDict()
od['a'] = 5
od['b'] = 7
od['c'] = 9
od['d'] = 11

for key, value in od.items():
    print(key, value)

Result:

This is an Ordered Dict:

a 5
b 7
c 9
d 11

Process finished with exit code 0