Python: List vs Tuple vs Dictionary vs Set

Should you choose Python List or Dictionary, Tuple or Set? The biggest difference between these data structures is their usage:

Lists - for ordered sequence of objects
Tuple - can be considered as immutable list
Python Set - unique list
Python Dictionary / dict - pair of key and values

The choice depends on several criteria like:

Item access
Operations
Performance
Looping techniques
Uniqueness
Mutability

How to choose? Below you can find short information with code examples and most popular operations for each structure.

List

Use a list if you have an ordered collection of items or sequence of objects. A list contain elements which are indexed from 0 and can be accessed by this index. Elements can be added, removed and updated. The whole list can be sorted and sliced. Mutable data structure. You can check the operation in the table below:

Set

Elements doesn't have order and duplicates. Big advantage of set is performance - they are extremely fast and has bonus operations like: intersection and union. Set is not hashable. More information here: Unordered collections of unique elements

Examples with sets

# definition
s1=set([1, 2, 3])
s=set()

# add elements
s.add(2)
s.add(3)

one=set([1, 2, 3, 4])
two=set([4, 5, 6, 7])

# union
one.union(two)   # {1, 2, 3, 4, 5, 6, 7}

# intersection
one.intersection(two)
one - two # {4}

Tuple

Elements can't be added, removed or replaced after declaration. Tuple is hashable while lists are not. Official docs: Tuples and Sequences

Basic usage of tuples

# definition
s1 = (1, 2, 3, 4)
s2 = ()
s3 = ('a', 0, 3.14)

# operations
s1.count(1) # 1
s1.index(1) # 0

Dictionary

Use a dictionary when you have pairs of unique keys that map to values and there is a need for efficient look up by key. For dictionaries - there is index of keys - which should be unique. Each key has matching value. There's no ordering for Dictionaries and it's not natural to get first or last element( it might be possible in some situations). You can add, remove or modify values of dictionaries. You can check the operation in the table below:

Below you can find simple table which is going to help you with this choice between List and Dict for Python:

Python List vs Dictionary CheatSheet

Comparison of most popular operation for Python List and Dictionary with examples. Table is perfect for beginners and advanced users and can be used in every day work.

	List	Dictionary
Example	[0, 1, 2]	{0: 'Mon', 1: 'Tue'}
Details	1. Order is important 2. Items can be repeated 3. Heterogeneous data 4. Slicing	1. Key : Value pairs 2. Keys should be unique, values not 3. Heterogeneous data 4. Access by key
When to use	Ordered sequence of items	Associate values with keys
Declaration	days=['Mon', 'Tue', 'Wed', 'Thu']	days = { 'Mon': 'Monday', 'Tue': 'Tuesday', 'Wed': 'Wednesday'}
Add item	days.extend('Fri') - change list days + 'Fri' - produce new list days.append('Fri') days.append(['Fri', 'Sun'])	days['Thu'] = 'Thursday'
Item access	days[0] - first days.index("Mon") - by index days[-1] - last	1. days['Mon'] 2. days.get('Mon', 'Fri') Python Get First/Last N Items of a Dict
Get default	try: day = days[11] except IndexError: day = 'Mon'	days.get('Mon', 'Fri')
Update item	days[0] = 'Monday'	days['Mon'] = 0
Remove item	del days[0] - by index days.remove('Monday') - value	del days['Mon']
Looping Techniques	for day in days(): print(day)	for k, v in days.items(): print(k, v)
Sort	days.sort()	1. by keys 2. by elements Python How to sort items in dictionary
Slicing	days[0:3] - start 0, end 2 days[:] - all items days[-1] - last element days[::-1] - reverse list	dict(itertools.islice(days.items(), 2)) - values
Compre- hensions	[x + ' is a day' for x in days]	{i : chr(65+i) for i in range(4)}
Check item existence	day in days	1. value - day in days.values() 2. key - days.get(day)
Docs	1. List methods 2. List Comprehensions	1. Dictionaries 2. Dict Comprehensions
Performance	Time Complexity List	Time Complexity Dict