Differences in list, tuple, set and dictionary in Python

List, tuple, set and dictionary are all built-in data types to store the data collections. List, tuple and set store multiple values in a single variable, while the dictionary stores data values in key:value pairs. This article will talk about the differences in the method of creating them, the key features, and the applications.

1. List

(1) Creation: square brackets

thislist =  ['blue', 'green', 'yellow', 'pink', 'white']

# or use the list constructor
thislist = list(('blue', 'green', 'yellow', 'pink', 'white'))

(2) Features

• Ordered: It means that the items in a list have a defined order, and that order will not change. It also means we could assess the items by indexing. For example,

print(thislist[2])  # returns 'yellow'
print(thislist[:3]) # returns ['blue', 'green', 'yellow']

• Changeable: It means we can change, add, and remove items in a list after it is created. For example,

thislist[0] = 'light blue' # change ‘blue’ to ‘light blue’
thislist.insert(2, 'the third place')  # insert the 'the third place' to the third place in the list
thislist.append('black')  # append the 'black' at the end of the list
thislist.remove('yellow') # remove the item 'yellow' in the list

• Allow duplicates: Since the list is indexed, it can have items with the same values. For example,

thislist2 = ['blue', 'green', 'yellow', 'blue']

(3) Applications

• Used in Array operations. We could use lists as arrays with built-in commands (NOTE: to work with arrays, you have to import a library like Numpy)
• Used in databases. We could create the database using list. Since it could store different data types, we use list and tuples here to make a database. For example,

thislist3 = [
('name', 'gender', 'subject', 'score'),
('John', 'M', 'Math', 90),
('Emily', 'F', 'Biology', 85),
('Helen', 'F', 'History', 92)]

• Used in JSON format. Convert Python list to JSON string. For example,

import json
thislist4 = [12, 45, 83, 9.5, 33.7, 98]
jsonStr = json.dumps(thislist4)
print(jsonStr) # returns [12, 45, 83, 9.5, 33.7, 98]

2. Tuple

(1) Creation: Use round brackets.

thistuple = ('John', 'M', 'Math', 90)

# or use the tuple constructor
thistuple = tuple(('John', 'M', 'Math', 90))

(2) Features

• Ordered
• Unchangeable: We cannot change, add, or remove items after the tuple is created.
• Allow duplicates

(3) Applications

• Used to insert records in the database through SQL query at a time

3. Set

(1) Creation: use curly brackets

thisset = {'apple', 'banana', 'cherry'}

# or use the tuple constructor
thisset = set(('apple', 'banana', 'cherry'))

(2) Features

• Unordered: It means you cannot refer items by indexes or keys.
• Unchangeable: (Although you cannot change its items, you could remove or add new items)

thisset.add('orange')
thisset.remove('apple')

• Do not allow duplicates: The set cannot contain the same values in one set.

(3) Applications

• Finding unique elements. For example,

thisset2 = {'apple', 'orange', 'apple'}
print(thisset2)  # returns { 'apple', 'orange'}

• Join operations. Two or more sets could be joined. For example,

thisset3 = {'grape', 'blueburry'}
thisset.union(thisset3)
# returns {'apple', 'banana', 'cherry', 'grape', 'blueburry'}

4. Dictionary

(1) Creation: use curly brackets with keys and values

thisdict = {
  'name': 'John',
  'gender': 'M'
  'subject': 'Math',
  'grade': 90}

(2) Features

• Ordered
• Changeable
• Do not allow duplicates: It cannot contain the same keys.

(3) Applications

• Used to create a dataframe with the list

import pandas as pd 
  
# list of name, gender, subject, and score
nme = ['John', 'Emily', 'Hellen']
gd = ['M', 'F', 'F']
sbj = ['Math', 'Biology', 'History']
scr = [90, 85, 92]
  
# dictionary of lists 
dict = {'name': nme, 'gender': gd, 'subject': sbj, 'score': scr} 
df = pd.DataFrame(dict)
df

• Used in JSON