Python - Collections Module

The collections module provides alternatives to built-in container data types such as list, tuple and dict.

namedtuple()

The namedtuple() function returns a tuple-like object with named fields. These field attributes are accessible by lookup as well as by index.

General usage of this function is:

collections.namedtuple(type_name, field-list)

The following statement declares a student class having name, age and marks as fields.

import collections

student = collections.namedtuple('student', [name, age, marks])

To create a new object of this namedtuple, do the following:

s1 = student("Imran", 21, 98)
print(s1.name)
print(s1.age)
print(s1.marks)

print(s1[0])
print(s1[1])
print(s1[2])

The example create an object of the student tuple and access the values of the field by using the dot notation s1.name and also using index s1[0].

OrderedDict()

The OrderedDict() function is similar to a normal dictionary object in Python. However, it remembers the order of the keys in which they were first inserted.

import collections

d1 = collections.OrderedDict()
d1['A'] = 65
d1['C'] = 67
d1['B'] = 66
d1['D'] = 68

for k,v in d1.items():
    print (k,v)

A 65
C 67
B 66
D 68

Upon traversing the dictionary, pairs will appear in the order of their insertion.

deque()

A deque object support appends and pops from either ends of a list. It is more memory efficient than a normal list object. In a normal list object, the removal of any item causes all items to the right to be shifted towards left by one index. Hence, it is very slow.

import collections

q = collections.deque([10,20,30,40])
q.appendleft(0)
print(q)

q.append(50)
print(q)

print(q.pop())
print(q)

print(q.popleft())
print(q)

Learn more about the collections module in Python docs.