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10.6: Chapter Summary

  • Page ID
    117590
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    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.

    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}
    
    Table 10.10 Chapter 10 reference.
    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]}

    This page titled 10.6: Chapter Summary is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by OpenStax via source content that was edited to the style and standards of the LibreTexts platform.