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.

Table 10.10: Chapter 10 reference.

Concept	Description
Dictionary creation using curly braces	my_dict = {key1:value1, key2:value2}
Dictionary creation using the dict() method	# 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)
Accessing dictionary items	my_dict = {key1: value1, key2: value2} # Accessing item using square bracket notation my_dict[key1] # Accessing item through get() method my_dict.get(key1)
Accessing all dictionary items	my_dict.items()
Accessing all dictionary keys	my_dict.keys()
Accessing all dictionary values	my_dict.values()
Adding a new key-value pair or updating an existing key-value pair	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})
Deleting a key-value pair from a dictionary	my_dict = {key1: value1, key2: value2} # Using del keyword del my_dict[key1] # Using pop() method deleted_value = my_dict.pop(key1)
Iterating over a dictionary	for key in dictionary: # Loop expression # Statements to execute in the loop #Statements to execute after the loop
Nested dictionaries	{ key_1:{key11:value11, key12:value12}, key_2:{key21:value21, key22:value22} }
Dictionary comprehension	{key_expression: value_expression for element in iterable}

Try It: Even and odd values

Given a list, create a dictionary with two keys, "even" and "odd". The values associated with each key must be the list of corresponding even and odd values in the given list.

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

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

[1]