Python Data Structures

This page provides an introduction to python data structures.

Lists

Lists are ordered and changable, and allow duplicates.

fruits = ["apple", "banana", "orange", "coconut"]
# o/p: ['apple', 'banana', 'orange', 'coconut']


print(fruits[0::2])
# o/p: ['apple', 'orange']


# length
len(fruits)
# o/p: 4


# in 
print("apple" in fruits)
# o/p: True


# reassign a value
fruits[0] = "pineapple"
# o/p: ['pineapple', 'banana', 'orange', 'coconut']


# append
fruits.append("apple")
# o/p: ['pineapple', 'banana', 'orange', 'coconut', 'apple']


# remove 
fruits.remove("pineapple")
# o/p: ['banana', 'orange', 'coconut', 'apple']


# insert 
fruits.insert(0, "pineapple")
# o/p: ['pineapple', 'banana', 'orange', 'coconut', 'apple']


# sort 
fruits.sort()
# o/p: ['apple', 'banana', 'coconut', 'orange', 'pineapple']


# reverse - just reverses a list not in any order.
fruits.reverse()
# o/p: ['pineapple', 'orange', 'coconut', 'banana', 'apple']


# index 
print(fruits.index("apple"))
# o/p: 4


# count
print(fruits.count("apple"))
# o/p: 1


# clear
fruits.clear()
# o/p: []


# lists all the methods availble for a collection
print(dir(fruits))

info

To list all the method available for a collection, call dir function.

Sets

Sets are unordered and doesn't allow duplicates.

fruits_set = {"apple", "banana", "orange", "coconut"}
# o/p: {'coconut', 'orange', 'apple', 'banana'}


# add 
fruits_set.add("pineapple")
# o/p: {'pineapple', 'orange', 'coconut', 'apple', 'banana'}


# remove 
fruits_set.remove("apple")
# o/p: {'pineapple', 'orange', 'coconut', 'banana'}


# pop
fruits_set.pop()
# o/p: 'pineapple'


# clean
fruits_set.clear()
# o/p: set()

Tuples

Tuples are ordered and unchangble, and allow duplicates.

fruits_tuple = ("apple", "orange", "banana", "coconut")


# len 
len(fruits_tuple)
# o/p: 4


# in 
"apple" in fruits_tuple
# o/p: True


# index 
fruits_tuple.index("apple")
# o/p: 0


# count 
fruits_tuple.count("coconut")
# o/p: 1

2D Lists

fruits_2d = ["apple", "banana", "orange"]
vegetables_2d = ["tomatos", "potatos"]


groceries = [fruits_2d, vegetables_2d]
# o/p: [['apple', 'banana', 'orange'], ['tomatos', 'potatos']]


# iterator over every elements
for collection in groceries:
  for food in collection:
    print(food, end =" ")
  print()
# o/p:
# apple banana orange
# tomatos potatos



exotic_vegetables_2d = [("lotus root", "karela")]
groceries.append(exotic_vegetables_2d)

for collection in groceries:
  for food in collection:
    print(food, end = " ")
  print()
# o/p:
# apple banana orange 
# tomatos potatos 
# ('lotus root', 'karela') 

Dictionaries

Dictionary is collection of key, value pair. It is ordered, changable, and doesn't allow duplicates.

capitals = {
  "India": "New Delhi",
  "United States of America": "Washington D.C"
}
# o/p: {'India': 'New Delhi', 'United States of America': 'Washington D.C'}


# get
print(capitals.get("United States of America"))
# o/p: Washington D.C


print(capitals.get("Japan"))
# o/p: None


# update
capitals.update({"Germany": "Berlin"})
# o/p: {'India': 'New Delhi', 'United States of America': 'Washington D.C', 'Germany': 'Berlin'}


# pop
capitals.pop("Germany")
# o/p:
# 'Berlin'
# {'India': 'New Delhi', 'United States of America': 'Washington D.C'}


# popitem - removes latest key value pair
capitals.popitem()
# o/p:
# ('United States of America', 'Washington D.C')
# {'India': 'New Delhi'}


# keys 
capitals.keys()
# o/p: dict_keys(['India'])


# iterate over keys
for key in capitals.keys(): print(key)
# o/p: India


# values
capitals.values()
# o/p: dict_values(['New Delhi'])


# items
capitals.items()
# o/p: dict_items([('India', 'New Delhi')])


# iterate over key, value
for key, value in capitals.items(): print(f"key: {key}, value: {value}")
# o/p: key: India, value: New Delhi

List Comprehensions

doubles = [x * 2 for x in range(1, 11)]
#o/p: [2, 4, 6, 8, 10, 12, 14, 16, 18, 20] 


numbers = [-1, 4141.13, 44, -2, 2414, -3]
positive_numbers = [num for num in numbers if num >= 0]
# o/p: [4141.13, 44, 2414]


negative_numbers = [num for num in numbers if num < 0]
# o/p: [-1, -2, -3]

Sorting

# sorting list
fruits_list = ["Banana", "Apple", "Orage", "Coconut"]
fruits_list.sort()
print(fruits_list)



# sorting tuple
fruits_tuple = ("Banana", "Apple", "Orage", "Coconut")
fruits_tuple = tuple(sorted(fruits_tuple, reverse = True))
print(fruits_tuple)



# sorting dictionary
fruits_dict =  {"Banana": 105, "Apple": 72, "Orage": 73, "Coconut": 354}

# sorting by key
fruits_dict_by_key = dict(
  sorted(
    fruits_dict.items(), key=lambda item: item[0], reverse =True
  )
)

# sorting by value
fruits_dict_by_value = dict(
  sorted(
    fruits_dict.items(), key=lambda item: item[1], reverse =True
  )
)

print(fruits_dict_by_key)
# o/p: {'Orage': 73, 'Coconut': 354, 'Banana': 105, 'Apple': 72}

print(fruits_dict_by_value)
# o/p: {'Coconut': 354, 'Banana': 105, 'Orage': 73, 'Apple': 72}



# sorting objects
class Fruit:
  def __init__(self, name, calories):
    self.name = name
    self.calories = calories
    
  def __str__(self):
    return f"{self.name}: {self.calories}"
    
  def __repr__(self):
    return self.__str__()
    

fruits = [
  Fruit("banana", 105),
  Fruit("apple", 72),
  Fruit("orange", 73),
  Fruit("coconut", 354)
]


# sorting by name
fruits_sorted_by_name = sorted(fruits, key=lambda fruit: fruit.name, reverse=True)
for fruit in fruits_sorted_by_name: print(str(fruit))
# o/p:
# orange: 73
# coconut: 354
# banana: 105
# apple: 72


# sorting by calories
fruits_sorted_by_calories = sorted(
  fruits, key=lambda fruit: fruit.calories, reverse=True
)
for fruit in fruits_sorted_by_calories: print(str(fruit))
# o/p:
# coconut: 354
# banana: 105
# orange: 73
# apple: 72