Sets contain unique values, as the definition suggests. Dictionaries are special form of sets that contain key:value pairs based on unique set of key entries. The same value can be reassigned to different keys. Any reassignment to or update() of a specific key will overwrite the existing value of that key. The set of keys in a dictionary can be retrieved by the keys() method.

The get() function has the similar result of accessing the dictionary items using the access operator []: 

balance_dict = {
"Alice":1345.345, 
"Claire":15642.432, 
"Spiderman":1234366.4352}

print("Alice has %10.2f units of balance\n" % (balance_dict.get("Alice")))

balance_dict["Alice"] = 3500.365


for key in balance_dict.keys():
    print("Balance of %10s is %10.2f" % (key, balance_dict[key]))
    if key == "Claire":
        balance_dict.update({"Claire":25000.453})
    print("Balance of %10s is %10.2f" % (key, balance_dict.get(key)))
    

Output:

Alice has    1345.35 units of balance

Balance of      Alice is    3500.36
Balance of      Alice is    3500.36
Balance of     Claire is   15642.43
Balance of     Claire is   25000.45
Balance of  Spiderman is 1234366.44
Balance of  Spiderman is 1234366.44

balance_dict = \
    {
"Alice":1345.345,
"Claire":12000,
"Spiderman":1234366.4352
    }

print("Alice has %10.2f units of balance\n" % (balance_dict.get("Alice")))

balance_dict["Alice"] = 3500.365


for key in balance_dict:

    print("Balance of %10s is %10.2f" % (key, balance_dict[key]))

    if key == "Claire":
        balance_dict.update({key: balance_dict.get(key) + 25000})
        balance_dict[key] += 10000

    print("Balance of %10s is %10.2f" % (key, balance_dict.get(key)))

One very important distinction between the get() function and the access operator [] is that the access operator causes the program to crash if the provided key does not exist in the dictionary. On the other hand, the get() function simply returns None in case the key does not exist.

So why have them both? The answer is that we cannot decide whether the given key is absent in the dictionary or the given key is present with a value None, just by looking at the result None. Depending on the use case, you can select the crashing option, returning None option, or checking whether the key is in the dictionary beforehand.

balance_dict = {
"Alice":1345.345, 
"Claire":15642.432, 
"Spiderman":1234366.4352}

print("Alice has %10.2f units of balance\n" % (balance_dict.get("Alice")))

print("Balance of Mirza : " , balance_dict.get("Mirza"))
print("Balance of Mirza : " , balance_dict["Mirza"])

print("Success.")

The get() function can also return a default value other than None if the key does not exist in the dictionary:

balance_dict = {
"Alice":1345.345, 
"Claire":15642.432, 
"Spiderman":1234366.4352}

print("Balance of Mirza : " , balance_dict.get("Mirza", 0))

print("Success.")

A view of dict_items can be generated by the items() method, where the view will be automatically updated if the dictionary is modified:

balance_dict = {
"Alice":1345.345, 
"Claire":15642.432, 
"Spiderman":1234366.4352}

print("Alice has %10.2f units of balance\n" % (balance_dict.get("Alice")))

items_view = balance_dict.items()
print(items_view)

balance_dict["Alice"] = 3500.365
print(items_view)

Output:

Alice has    1345.35 units of balance

dict_items([('Alice', 1345.345), ('Claire', 15642.432), ('Spiderman', 1234366.4352)])
dict_items([('Alice', 3500.365), ('Claire', 15642.432), ('Spiderman', 1234366.4352)])

The in keyword acts as an iteration operator when used in a for loop. Similar to the strings and lists, the in keyword can be used to find out whether a given argument is present in a set or in the key set of a dictionary:

balance_dict = {
"Alice":1345.345, 
"Claire":15642.432, 
"Spiderman":1234366.4352}

def display_balance(account_owner):
    if account_owner in balance_dict:
        print("%15s has %10.2f units of balance" % (account_owner, balance_dict.get(account_owner)))
    else:
        print("%15s does not have an account" % account_owner)


display_balance("Alice")
display_balance("Batman")

Output:

          Alice has    1345.35 units of balance
         Batman does not have an account