List

List is a data structure which can hold items regardless of their type. It can hold integers, strings, complex numbers etc. It can also hold many lists within itself. It is created by entering comma separated items in square brackets. For example :

a_list = [1,2,3,'hello']; print (a_list)

## [1, 2, 3, 'hello']

Check the methods associated with the list by typing dir(a_list).

Before going further we talk about mutable and immutable data structures.

• Mutable data structures are those data structures which can be altered in place. Which means we can delete an item, replace an item, alter an item, append an item inside that data structure.

• Immutable data structures are those data structures which can not be altered in place. We can make copy of it with the changes to a different variable but we can not make any in place changes.

We will further look at examples to understand this.

Tuple

Tuple is also a data structure which can hold items regardless of their type just like a list. It is created by entering comma separated items in parenthesis. For example :

a_tuple = (1,2,3,'hello',1.2); print (a_tuple)

## (1, 2, 3, 'hello', 1.2)

Again check the methods associated with the tuple by typing dir(a_tuple). You will find that some methods available for list like pop, delete, append etc are missing for tuple. This is because a tuple is immutable. To change a tuple you need to create another tuple with the changes.

a_list.append(10)
print (a_list)

## [1, 2, 3, 'hello', 10]

If you try a_tuple.append(10), it will throw up error because tuple is an immutable object.

print (a_tuple)

## (1, 2, 3, 'hello', 1.2)

new_tuple = (10,11)
print (new_tuple)

## (10, 11)

final_tuple = a_tuple + new_tuple
print (final_tuple)

## (1, 2, 3, 'hello', 1.2, 10, 11)

The important difference between a list and a tuple is that all things being same, a list is a mutable container of items, a tuple on the other hand is immutable.

For this very reason, iterating over a tuple is always faster than iterating over a list.

We will talk about iterating over list, tuple and dictionary later.

Dictionary

Dictionary is the most versatile and probably the most helpful data structure in python.

Dictionary is also a mutable container of items but in dictionary we can assign each item or a list/tuple of items a key. A key acts as an identifier to a particular item or a list of items. A dictionary is created by entering comma separated key value pairs in curly brackets. Key value pairs hold a colon between them. For example :

a_dict = {'Name':'Puneet', 'Date of Birth':6, 'Month of Birth':11, 'Year of Birth':1988, 'Lab mates': ['Ram','Amit','Satya']}

print (a_dict.keys())

## ['Month of Birth', 'Date of Birth', 'Year of Birth', 'Lab mates', 'Name']

print (a_dict.values())

## [11, 6, 1988, ['Ram', 'Amit', 'Satya'], 'Puneet']

You will see that, once the dictionary is created, the order of printed items (keys) is not same as the order of entered items. But no need to worry! You can always access any item with its key.

print (a_dict['Name'])

## Puneet

Please note that a dictionary is a mutable data structure.

Subsetting, iterating over data structures and different control statements will be covered in the next post.

Phew!! That was a lot to talk about. I need a drink.