Collections in Python

Python collections are just containers which can contain data objects of various data-types inside them. Each collection type has their own features which we will look at in this lesson. Let’s study about these collections and their most used data-types.

Type of Collections

We will study following collections in Python in this lesson:

OrderedDict
defaultdict
counter
namedtuple
deque

OrderedDict

When order of insertion of the key and value matters for the program, we should make use of OrderedDict collection. Also, when the value for the same key is inserted, last value is overwritten with the new value. Let us take a look at a sample program:

from collections import OrderedDict

author = OrderedDict([
(1, ‘David’),
(2, ‘Shubham’),
(3, ‘Swapnil Tirthakar’),
])

for num, name in author.items():
print(num, name)

Here is what we get back with this command:

OrderDict collection in Python

defaultdict

Next collection in Python is defaultdict. This collection can contain duplicate keys. The main advantage of this collection is that we can collect values which belong to the identical keys. Let’s look at a program which demonstrates the same:

from collections import defaultdict

grade = [
(‘Shubham’, ‘B’),
(‘David’, "A"),
(‘LinuxHint’, ‘B’),
(‘LinuxHint’, ‘A’)
]

dict_grade = defaultdict(list)

for key, value in grade:
dict_grade[key].append(value)

print(list(dict_grade.items()))

Let’s see the output for this command:

DefaultDict collection in Python

Here, the items related to same key LinuxHint were collected and shown in the output as together.

counter

The Counter collections allow us to count all the values which are present in the collection against the same key. Here is a program to show how the counter collection works:

from collections import Counter

marks_collect = [
(‘Shubham’, 72),
(‘David’, 99),
(‘LinuxHint’, 91),
(‘LinuxHint’, 100)
]

counted = Counter(name for name, marks in marks_collect)
print(counted)

Here is what we get back with this command:

Counter collection in Python

This provides a very easy way to count items in a Puython collection.

namedtuple

We can also have collection of items where values are assigned to a named key. This way, it is easy to access a value which is assigned to a name instead of an index. Let us look at an example:

import collections

Person = collections.namedtuple(‘Person’, ‘name age gender’)
oshima = Person(name=‘Oshima’, age=25, gender=‘F’)
print(oshima)

print(‘Name of Person: {0}’.format(oshima.name))

Let’s see the output for this command:

Named Tuple collection in Python

deque

As a final example, we can maintain a collection of items and remove characters form it as a deque process. Let us look at an example for the same:

import collections

person = collections.deque(‘Oshima’)
print(‘Deque :’, person)
print(‘Queue Length:’, len(person))
print(‘Left part :’, person[0])
print(‘Right part :’, person[–1])

person.remove(‘m’)
print(‘remove(m):’, person)

Here is what we get back with this command: