Dictionary
Dictionary
Dictionaries are unordered, mutable collections of key-value pairs. Beyond basic usage (dict[key] = value),
def add(a, b): return a + b
def sub(a, b): return a - b
def multiply(a, b): return a * b
def divide(a, b): return a / b if b != 0 else "Error"
if __name__ == "__main__":
dictionary = {
"name":"dinesh",
"address":"baneshwor",
"hobby":["reading",'watching movies',"watching tennis","watching cricket"],
}
print(dictionary)
# Adding new Item to dictionary using update method
dictionary.update({"fav_movies":["Gone with the Wind","Borken Arrow"]})
print(dictionary)
# Adding new Item to dictionary
dictionary["books"] = ["DSA","DBMS","Programming"]
print(dictionary)
# Accesing dictionary items
print("Name: ",dictionary["name"])
l = dictionary["books"]
print("Books: ",l)
print("Favorite Movies: ",dictionary["fav_movies"])
print("Keys: ",dictionary.keys())
print("Values: ",dictionary.values())
print("Items: ",dictionary.items())
#changing item of dicitonary
dictionary["address"] = "New Baneshwor"
print("New Address: ",dictionary["address"])
#chaing item of dictionary using update method
dictionary.update({"address":"New Baneshowr, Kathmandu"})
print("Address changed using update : ",dictionary["address"])
#removing items from dictionary
dictionary.pop("address")
print("After removing address: ",dictionary)
#REMOVING LAST ITEM INSERTED TO THE DICTIONARY - popitem()
dictionary.popitem()
#looping through dictionary
print("using for loop to accessing dictionary items: only keys will be displayed")
for x in dictionary:
print(x)
#display values of keys
for x in dictionary:
print(dictionary[x])
#displaying values using values method
for x in dictionary.values():
print("using values(): ",x)
# displaying both keys and values
for k,v in dictionary.items():
print(k," : ",v)
#removing all items from dictinary
dictionary.clear()
print("After clear: ",dictionary)
# deleting dictionary completely
del dictionary
# print(dictionary) this will result in error
#using methods as values in dictionary
ops = {'+': add, '-': sub}
print(ops['+'](10, 5)) # Output: 15
d = {'apple': 3, 'banana': 1, 'orange': 2}
sorted_by_value = dict(sorted(d.items(), key=lambda item: item[1]))
print(sorted_by_value) # Output: {'banana': 1, 'orange': 2, 'apple': 3}
d = {'x': 10, 'y': 20}
print(d.keys()) # dict_keys(['x', 'y'])
print(d.values()) # dict_values([10, 20])
print(d.items()) # dict_items([('x', 10), ('y', 20)])
students = {
'Alice': {'age': 20, 'grade': 'A'},
'Bob': {'age': 22, 'grade': 'B'}
}
print(students['Alice']['grade']) # Output: A
students = {
'Alice': {'Math': 90, 'English': 85, 'Science': 92},
'Bob': {'Math': 78, 'English': 82, 'Science': 88},
}
# Average grade for each student
for name, subjects in students.items():
avg = sum(subjects.values()) / len(subjects)
print(f"{name}: {avg:.2f}")
#Create a dictionary of squares of even numbers only:
squares = {x: x ** 2 for x in range(10) if x % 2 == 0}
print(squares) # Output: {0: 0, 2: 4, 4: 16, 6: 36, 8: 64}
# Dictionary of Functions (Dispatch Table): Dynamic function selection:
operations = {'+': add, '*': multiply, '/': divide}
a, b = 10, 5
op = '*'
result = operations[op](a, b)
print(result) # Output: 50
# Using setdefault() for Grouping
names = ['Alice', 'Bob', 'Charlie', 'David', 'Amanda']
groups = {}
for name in names:
key = name[0]
groups.setdefault(key, []).append(name)
print(groups)
# Output: {'A': ['Alice', 'Amanda'], 'B': ['Bob'], 'C': ['Charlie'], 'D': ['David']}