10.6 Chapter summary

Highlights from this chapter include:

• A dictionary in Python is a container object including key-value pairs.
• The dict type implements a dictionary in Python.
• A dictionary cannot have duplicate keys.
• A dictionary is a mutable object but keys in the dictionary must be immutable objects.
• A dictionary can be created using curly braces or the dict() method.
• Values in the dictionary can be obtained through square bracket notation or the get() method.
• Dictionary items, keys, and values can be obtained using items(), keys(), and values() methods, respectively.
• Existing items can be modified or new items can be added to a dictionary using square brackets notation or the update() method.
• Items can be removed from a dictionary using the del keyword or the pop() method.
• Conditional statements can be used with a dictionary to check if the dictionary contains specific keys, values, or key-value pairs.
• Looping on a dictionary can be done by iterating over keys, values, or items.
• Nested dictionaries are dictionaries that are stored as values within another dictionary.
• With dictionary comprehension, elements of an iterable object are transformed into key-value pairs.

At this point, you should be able to use dictionaries in your programs. The programming practice below ties together most topics presented in the chapter.

my_dict = {key1:value1, key2:value2}

# Using a list
my_list = [(key1, value1), (key2, value2)]
my_dict = dict(my_list)

# Using keyword arguments
my_dict = dict(key1=value1, key2=value2)

# From another dictionary
old_dict = {key1: value1, key2: value2}
new_dict = dict(old_dict)

my_dict = {key1: value1, key2: value2}

# Accessing item using square bracket notation
my_dict[key1]

# Accessing item through get() method
my_dict.get(key1)

my_dict.items()

my_dict.keys()

my_dict.values()

my_dict = {key1: value1, key2: value2}

# Updating an item using square bracket notation
my_dict[key1] = new_value
# Adding a new key-value pair using square bracket notation
my_dict[key3] = value3

# Updating an item using update() method
my_dict.update({key1: new_value})
# Adding a new key-value pair using update() method
my_dict.update({key3: value3})

my_dict = {key1: value1, key2: value2}

# Using del keyword
del my_dict[key1]

# Using pop() method
deleted_value = my_dict.pop(key1)

for key in dictionary: # Loop expression
  # Statements to execute in the loop

#Statements to execute after the loop

{
key_1:{key11:value11, key12:value12},
key_2:{key21:value21, key22:value22}
}

{key_expression: value_expression for element in iterable}

    Input:
    input_list = [3, 5, 6, 1]
    

    Prints {"even": [6], "odd":[3, 5, 1]}