23_data_structures.py

#======================================================================================
#                               Data Structures
#--------------------------------------------------------------------------------------
# In python, data structures are ways to organize and store data efficiently
# python provides built-in data structures that are easy to use
# Main Data Structures in Python
#   List        ex:[1,2]
#   Tuple        ex:(1,2)
#   Set         ex:{1,2}
#   Dictionary  ex:{'a':1, 'b':2}
#======================================================================================

#--------------------------------------------------------------------------------------
# Data structure   |     Ordered   |  Allows duplicates    |   Indexed  |   Mutable   
#--------------------------------------------------------------------------------------
#   List           |     Yes       |  Yes                  |   Yes      |   Yes
#   Tuple          |     Yes       |  Yes                  |   Yes      |   No   
#   Set            |     No        |  No                   |   No       |   Yes
#   Dictionary     |     Yes       |  Only for keys        |   Keyed    |   Yes
#--------------------------------------------------------------------------------------

#--------------------------------------------------------------------------------------
# List --> A list stores multiple items in a single variable.
#--------------------------------------------------------------------------------------
#   Features:
#       * Ordered
#       * Mutable(can change)
#       * Allows Duplicate values
#--------------------------------------------------------------------------------------

my_list = [50, 30, 40, 50, 30]
print(my_list)          # Ordered, Allow duplicates
print(my_list[1])       # Indexed
my_list[-1] = 10
print(my_list)          # Mutable

#--------------------------------------------------------------------------------------
# Tuple --> A tuple is similar to a list but cannot be changed after creation.
#--------------------------------------------------------------------------------------
#   Features:
#       * Ordered
#       * Immutable(unchangeable)
#       * Allows duplicates
#--------------------------------------------------------------------------------------

my_tuple = (10, 20, 30, 10, 10)
print(my_tuple)     # Ordered, Allows Duplicates
print(my_tuple[0])  # Indexed
#my_tuple[-1] = 20  # Tuple is immutable
print(sorted(my_tuple)) 
print(type(sorted(my_tuple)) )  # List

#--------------------------------------------------------------------------------------
# Set --> A set stores unordered collection of unique values
#--------------------------------------------------------------------------------------
#   Features:
#       * Unordered
#       * Mutable
#       * No duplicates
#--------------------------------------------------------------------------------------

my_set = {10, 20, 30, 40, 20, 20}
print(my_set)       # Unordered, Unique
#print(my_set[0])   # Not indexed
my_set.remove(20)
print(my_set)       # Mutable

#--------------------------------------------------------------------------------------
# Set Methods
#--------------------------------------------------------------------------------------
#   .add(item)
#   .update(iterable)
#   .remove(item)
#   .discard(item)
#   .clear()
#--------------------------------------------------------------------------------------

a = {10, 20, 30}

#--------------------------------------------------------------------------------------
# .add() --> inserts the item somewhere in the set, but only if it is new
#--------------------------------------------------------------------------------------

a.add(40)
print(a)

#--------------------------------------------------------------------------------------
# .update() --> merges another group of values(iterable) into the set
#--------------------------------------------------------------------------------------


a.update([50, 60, 70])
print(a)
a.update("HI")
print(a)
a.update({80, 90})
print(a)

#--------------------------------------------------------------------------------------
#NOTE you can use math operators as quick shortcuts: | & - ^
#--------------------------------------------------------------------------------------

# |= works like update for sets
a |= {100, 200, 300}
print(a)

#--------------------------------------------------------------------------------------
# .remove() --> removes an item
#--------------------------------------------------------------------------------------

a.remove(300)
print(a)

# if item does not exist: It throws an error
# a.remove(150) # keyerror

#--------------------------------------------------------------------------------------
# .discard() --> removes the item if it exists and does nothing if it does not
#--------------------------------------------------------------------------------------

a.discard(10)
print(a)
a.discard(1000)
print(a)

#--------------------------------------------------------------------------------------
# .pop() --> pop removes a random item form a set
#--------------------------------------------------------------------------------------
a.pop()
print(a)

#--------------------------------------------------------------------------------------
# .clear() --> removes all items
#--------------------------------------------------------------------------------------
b = {1,3,4,5,9,8}
print(b)
b.clear()
print(b)
print()

#--------------------------------------------------------------------------------------
# Set Math Methods
#--------------------------------------------------------------------------------------
#NOTE: math operator returns a new set and leave the originals untouched
#   .union()
#   .intersection()
#   .difference() 
#   .symmetric_difference()
#--------------------------------------------------------------------------------------

a = {10, 20, 30, 40, 50}
b = {30, 40, 50, 60, 70}

#--------------------------------------------------------------------------------------
# .union() --> combines all unique items form both sets
#--------------------------------------------------------------------------------------
print(a.union(b))
# shortcut
print(a | b)

#--------------------------------------------------------------------------------------
# .intersection() --> returns only the shared items
#--------------------------------------------------------------------------------------
print(a.intersection(b))
# shortcut
print(a & b)

#--------------------------------------------------------------------------------------
# .difference() --> items in first set but not second
#--------------------------------------------------------------------------------------
print(a.difference(b))
# shortcut
print(a - b)    # returns items in 'a', but not in 'b'
print(b - a)    # returns items in 'b', but not in 'a'

#--------------------------------------------------------------------------------------
# .symmetric_difference() --> items in both sets except common items
#--------------------------------------------------------------------------------------
print(a.symmetric_difference(b))
# shortcut
print(a ^ b)
# or
print(b ^ a)

print()
#--------------------------------------------------------------------------------------
# Set Relationship Method
#--------------------------------------------------------------------------------------
#   .issubset()
#   .issuperset()
#   .isdisjoint()
#--------------------------------------------------------------------------------------

a = {1,2,3}
b = {6, 5, 3, 1, 4, 2}

#--------------------------------------------------------------------------------------
# .issubset() --> checks if all items of one set exist in another
#--------------------------------------------------------------------------------------
print(a.issubset(b))

#--------------------------------------------------------------------------------------
# .issuperset() --> checks if set contains another set
#--------------------------------------------------------------------------------------
print(b.issuperset(a))

#--------------------------------------------------------------------------------------
# .isdisjoint() --> checks whether sets have no common items
#--------------------------------------------------------------------------------------

a = {1,2}
b = {3,4}
print(a.isdisjoint(b))

#--------------------------------------------------------------------------------------
# Dictionary --> A dictionary stores data in 'key : value' pairs
#--------------------------------------------------------------------------------------
#   Features:
#       * Ordered (python 3.7+)
#       * Mutable
#       * keys must be unique
#--------------------------------------------------------------------------------------
my_dict = {'a':10, 'b':20, 'c':20, 'a':40, 'a':50}
print(my_dict)        # Ordered, Keys are unique, Values Allow Duplicates
# print(my_dict[1])   # Not Indexed
print(my_dict['a'])   # You access values by using their keys, not indexes
my_dict['b'] = 80     # Mutable
print(my_dict)


#--------------------------------------------------------------------------------------
# Dictionary Methods
#--------------------------------------------------------------------------------------
#   .get()
#   .in operator
#   .key()
#   .value()
#   .items()
#   .update()
#   .pop()
#   .popitem()
#   .fromkeys()
#--------------------------------------------------------------------------------------


student = {'name':"Bob", 'age':25, 'marks':90}

# Access
print(student['name'])
#print(student['city'])  # If the key is not found, Python throws error

#--------------------------------------------------------------------------------------
# .get() --> # Missing key returns None or your default value
#--------------------------------------------------------------------------------------
print(student.get('city'))
print(student.get('id', "Unknown"))

#--------------------------------------------------------------------------------------
# in operator --> tests if the key is inside the dictionary
#--------------------------------------------------------------------------------------

print('age' in student)
print('name' in student)
print('city' in student)

#--------------------------------------------------------------------------------------
# .key() --> Returns all keys in dictionary
#--------------------------------------------------------------------------------------
print(student.keys())

#--------------------------------------------------------------------------------------
# .value() --> Returns all values in dictionary
#--------------------------------------------------------------------------------------
print(student.values())

#--------------------------------------------------------------------------------------
# .items() --> Returns key-value pairs of your dictionary
#--------------------------------------------------------------------------------------
print(student.items())
print(student)

#--------------------------------------------------------------------------------------
# .items() use cases
# Perfect when you need key and value together
# for looping, transforming data, building new dicts, comparing and more
#--------------------------------------------------------------------------------------

for i in student:
    print(i, student[i])

for key, value in student.items():
    print(key, value)

#--------------------------------------------------------------------------------------
# .update() --> adds or updates key-value pairs
#--------------------------------------------------------------------------------------
student.update({'city':'mumbai', 'name':"john", 'marks':80, 'email':'john@gmail.com'})
print(student.items())

#--------------------------------------------------------------------------------------
# .pop() --> removes a key from the dictionary and returns its value
#--------------------------------------------------------------------------------------
age = student.pop('age')
print(student)
print(age)

#student.pop('country') # If the key is not found, Python throws  a keyerror
#--------------------------------------------------------------------------------------
# .pop() --> removes key and returns its value, or returns your default 
# if the key is missing
#--------------------------------------------------------------------------------------

country = student.pop('country', 'Unknown')
print(student)
print(country)

#--------------------------------------------------------------------------------------
# .popitem() --> returns and delete the most recent key value pair from the dictionary
#--------------------------------------------------------------------------------------

rm_pair = student.popitem()
print(student)
print(rm_pair)

#--------------------------------------------------------------------------------------
# .fromkeys() --> builds a new dictionary where all keys get the same default value
#--------------------------------------------------------------------------------------

user = dict.fromkeys(['id', 'name', 'age', 'city'], None)
print(user)

#--------------------------------------------------------------------------------------
# Easy Memory Trick
#--------------------------------------------------------------------------------------
#   List        --> Editable collection
#   Tuple       --> Fixed collection
#   Set         --> Unique values only
#   Dictionary  --> Key-value data
#--------------------------------------------------------------------------------------