Python Collections Concepts

Python Collections

In this article we will be looking at the list types of Python. Each of these collections is unique in their own way and are useful for various operations when programming.

We will be taking a look at:

Lists
Tuples
Sets
Dictionaries

Lists

A list is a collection which is ordered and changeable. In Python, lists are written with square brackets. They are also mutable.

This is how we create a list in Python:

                        
                            myList = ["computer","laptop","iphone"]
print(myList)

#output will be:
["computer","laptop","iphone"]

To access a single item in the list you will need to print the name of the list along with the position (in numbers) of the list item, in block brackets, starting from 0. Also, you can also use negative numbers (from -1) to access the LAST number in the list and increasing negative numbers will basically work your way backwards through the list. As shown below:

                        
                            myList = ["computer","laptop","iphone"]
print(myList[2])
print(myList[-3])

#outputs will be:
iphone
computer

There are other ways you can manipulate lists such as using ranges, deleting, changing item values, looping through lists, clearing a list, copying a list, joining lists and using constructors to make lists. These are useful as lists are more flexible to use.

Tuples

A Tuple is a collection of Python objects separated by commas. In someways a tuple is similar to a list in terms of indexing, nested objects and repetition but a tuple is immutable unlike lists which are mutable.

To crete a Tuple please look at the example below:

                        
                            my_tuple = ()
print (my_tuple)

# output will be 
()

The output is nothing because we declared Tuple which was empty. What if we create a non-empty Tuple?

                        
                            #normal way:
tup = 'Jay','solo'
print(tup)

#alternative way:
tup = ('Jay','solo')
print(tup)

# output will be
('Jay','solo')
('Jay','solo')
                            
                        
                    

You can perform various operations on tuples, such as concatenation, nesting tuples inside other tuples, repetition, slicing, deletion, length finding, converting to a list, looping, and using min() and max() (which could be used to find out min max values of the tuples etc). These make tuples really useful in the long run. Also remember, tuples are immutable whereas lists are mutable.

Sets

A set is an unordered collection of items. Every element is unique and must be immutable. However the set itself is mutable - we can add or remove items from it. Sets can also be used to perform mathematical set operations like union, intersection, symmetric difference etc.

To create a set, place all the items you want inside curly brackets {}, separated by comma or by using the built-in funtion, set(). You can have any sorts of data types in the set as long as they are not mutable, like lists.

                        
                            # set of strings
theSet = {"L","E","A","R","N"}
print(theSet)

# set of mixed datatypes
theSet = {4.3,"hi",(5,4,1),false}
print(theSet)

# output will be:
{"L","E","A","R","N"}
{4.3,"hi",(5,4,1),false}
                            
                        
                    

There are many more things you can do with set such as using methods, built-in functions and features. Please take a look at the sources below.

Dictionaries

A Dictionary is a type of list which contains keys and values. Each key is separated from its value by a colon (;), the items are separated by commas, and the whole thing is enclosed in curly brackets. An empty dictionary without any items is written with just two curly brackets, like this: {}.

Keys are unique within a dictionary, while values may not be. The values of a dictionary can be of any type, but the keys must be of a immutable data type such as strings, numbers, or tuples.

To access values in a dictionary you can use the square brackets along with the correct key to obtain its value.

                        
                            dict = {'Drink':'Water','Price':5,'Type':'Small'}
print "dict['Drink']:", dict['Drink']
print "dict['Price']:", dict['Price']

# output will be this:
dict['Drink']: Water
dict['Price']: 5

You can also update dictionaries by adding new entries, or key value pairs, modifying an extisting entry or deleting an existing entry. There are also lots of other things you can do with dictionaries such as checking the properties of them, using the methods and built-in functions. Dictionaries are very similar to objects as well.

Sources: (click on them to see them)