Update lists, sets, tuples, dict

Author: Sahil

day3/dictionaries.py

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+# dict allows us to store data in (key, value) pairs
+# themselves are mutable but can contain only immutable types as keys, like sets
+# very useful for accessing data based on a key, quickly
+
+# creating empty dict
+day_mapping = {}
+day_mapping = dict()
+
+# dict with items (key, value) pairs
+day_mapping = {
+  "Monday": 1,
+  "Tuesday": 2,
+  "Wednesday": 3,
+  "Thursday": 4,
+  "Friday": 5,
+  "Saturday": 6,
+  "Sunday": 0
+}
+print(len(day_mapping)) # 7
+
+# items can be accessed based on the key, not the index
+print(day_mapping["Wednesday"]) # 3
+print(day_mapping.get("Sunday"))
+print(day_mapping.get("sunday")) # None, because the key is not present
+
+# updating value for a particular key
+day_mapping["Sunday"] = 7
+# adding another key
+day_mapping["Default"] = 0
+
+# keys, values and items
+print(day_mapping.keys())
+print(day_mapping.values())
+print(day_mapping.items())
+
+# removing a particular key
+del(day_mapping["Default"])
+print(day_mapping.keys())

day3/lists.py

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+# lists: container objects used to store related items together
+# let us say you were to input n numbers from user and find their sum, average, etc.
+# also you need the ability to sort the numbers etc
+# so you need some data type to store them easily, take input and print some required data
+
+number_list = []
+number_list = [10, 4, 1, 5]
+print(type(number_list))
+
+# 0-based indexing to access elements in the list
+# order is retained in the list!
+first_num = number_list[0]
+last_num = number_list[-1]
+print(f"First: {first_num}, Last: {last_num}")
+
+# common methods on lists
+print(f"Number list: {number_list}")
+
+num_count = len(number_list)
+print(f"Count: {num_count}")
+
+number_list.append(7)
+print(f"Appended 7: {number_list}")
+
+number_list.insert(1, 6)
+print(f"Insert 6 at index 1: {number_list}")
+
+number_list.pop()
+print(f"Removed the last element: {number_list}")
+
+# lists are mutable, can change the elements in-place
+# sorting lists, sorted method returns a new list
+ordered_num_list = sorted(number_list)
+print(f"Ordered number list: {ordered_num_list}")
+print(f"Original number list: {number_list}")
+
+# sorting in place, descending order
+number_list.sort(reverse=True)
+print(f"Original number list: {number_list}")
+# reversing a list in-place
+number_list.reverse()
+print(f"Reversed number list: {number_list}")
+
+# extending one list into another
+l1 = [1, 2, 3, 4]
+l2 = [5, 6, 7, 10]
+l1.extend(l2)
+print(l1)
+print(l2)
+
+# checking if an item is present in a list (in keyword)
+print(5 in l1)
+print(8 in l2)
+
+# split and join
+input_str = "1 2 3 4 5 6"
+input_list = input_str.split()
+print(input_list)
+
+print(','.join(input_list))

day3/sets.py

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+# sets help to store data in an unsorted way
+# an item can only be present once in a set, i.e. no duplicates
+# membership test is very fast
+# other powerful operations provided are: union, difference and intersection
+
+prime_set = set()
+prime_set.add(1)
+prime_set.add(2)
+prime_set.add(3)
+prime_set.add(11)
+# order is not preserved in a set
+print(f"Prime set: {prime_set}")
+
+# remove an item from a set
+prime_set.discard(1)
+print(f"Prime set: {prime_set}")
+
+# x = prime_set[0] # cannot access set items using an index
+# prime_set.sort() # cannot sort items in a set
+# sorted method can still be used as that will convert set to a list
+
+# single element set
+s = {1}
+print(s)
+print(type(s))
+
+s = {}
+print(type(s)) # <class 'dict'>
+# to create empty set, rather use set constructor
+s = set()
+print(type(s)) # <class 'set'>
+
+prime_set = {2, 3, 5, 5, 3, 7}
+print(prime_set) # duplicate values not present
+
+# sets internally use hashing to store the elements and check if it is present or not
+# a numerical value is associated with any item in the set, try using hash() method
+# hash() function works only on immutable data types, so you cannot create a set of mutable types
+
+names = {"scaler", "interviewbit", "scaler"}
+print(names)
+# both the following hash values will come out to be same! although values can change
+# depending on when the program is run
+print(hash("scaler"))
+print(hash("scaler"))
+
+# set_of_lists = {[1, 2, 3], [1, 2, 3, 4]} # TypeError: unhashable type: 'list'
+
+# we can convert a list into a set using the set constructor
+names = ["scaler", "interviewbit", "scaler"]
+names_set = set(names)
+print(names_set)
+
+# update is used to update set with another sequence
+prime_set.update(names_set)
+print(prime_set)
+prime_set.update("scaler")
+# since string is a sequence, each of its characters will get added to the set!
+print(prime_set)
+
+# union (|), intesection (&), difference (^)

day3/tuples.py

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+# tuples are used to keep track of related but different items
+# they are immutable, you cannot change the items in it once created!
+# a use-case could be to store a row in a spreadsheet, given that 
+# we need read-only snapshot of data
+
+point = ()
+# point = collection of x, y and z coordinates!
+point = (3, 4, 5)
+print(point)
+print(type(point))
+
+# checking for existence of an item
+print(3 in point)
+print(6 in point)
+
+# access item using index as well
+print(f"x = {point[0]}, y = {point[1]}, z = {point[2]}")
+
+# point[0] = 10 # TypeError: 'tuple' object does not support this assignment
+
+# to create single item tuple, we need to give a comma after the item
+single_element = (1)
+print(type(single_element)) # <class 'int'>
+
+single_element = (1, )
+print(single_element)
+print(type(single_element)) # <class 'tuple'>
+
+# unpacking tuple data
+x, y, z = point
+print(x, y, z)
+
+# functions can as well return multiple values with the help of tuples