Approach #4: Unpacking with. Unpacking with. works with any object that is iterable and, since dictionaries return their keys when iterated through, you can easily create a list by using it within a list literal. A Dictionary contains a collection of key/value pairs. Its Add method takes two parameters, one for the key and one for the value. One way to initialize a Dictionary, or any collection whose Add method takes multiple parameters, is to enclose each set of parameters in braces as shown in the following example.

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A Dictionary<TKey,TValue> contains a collection of key/value pairs. /download-wic-reset-key-generator.html. Its Add method takes two parameters, one for the key and one for the value. One way to initialize a Dictionary<TKey,TValue>, or any collection whose Add method takes multiple parameters, is to enclose each set of parameters in braces as shown in the following example. Another option is to use an index initializer, also shown in the following example.

Example

In the following code example, a Dictionary<TKey,TValue> is initialized with instances of type StudentName. The first initialization uses the Add method with two arguments. The compiler generates a call to Add for each of the pairs of int keys and StudentName values. The second uses a public read / write indexer method of the Dictionary class:

Note the two pairs of braces in each element of the collection in the first declaration. The innermost braces enclose the object initializer for the StudentName, and the outermost braces enclose the initializer for the key/value pair that will be added to the studentsDictionary<TKey,TValue>. Finally, the whole collection initializer for the dictionary is enclosed in braces. In the second initialization, the left side of the assignment is the key and the right side is the value, using an object initializer for StudentName.

See also

Dictionary

A dictionary is a collection which is unordered, changeable and indexed. In Python dictionaries are written with curly brackets, and they have keys and values.

Example

Create and print a dictionary:

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Accessing Items

You can access the items of a dictionary by referring to its key name, inside square brackets:

Example

Get the value of the 'model' key:

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There is also a method called get() that will give you the same result:

Example

Get the value of the 'model' key:

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Change Values

You can change the value of a specific item by referring to its key name:

Example

Change the 'year' to 2018:

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Loop Through a Dictionary

You can loop through a dictionary by using a for loop.

When looping through a dictionary, the return value are the keys of the dictionary, but there are methods to return the values as well.

Example

Print all key names in the dictionary, one by one:

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Example

Print all values in the dictionary, one by one:

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Example

You can also use the values() function to return values of a dictionary:

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Example

Loop through both keys and values, by using the items() function:

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Check if Key Exists

To determine if a specified key is present in a dictionary use the in keyword:

Example

Check if 'model' is present in the dictionary:

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Dictionary Length

To determine how many items (key-value pairs) a dictionary has, use the len() method.

Example

Print the number of items in the dictionary:

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Adding Items

Adding an item to the dictionary is done by using a new index key and assigning a value to it:

Example

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Removing Items

There are several methods to remove items from a dictionary:

Example

The pop() method removes the item with the specified key name:

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Example

The popitem() method removes the last inserted item (in versions before 3.7, a random item is removed instead):

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Example

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The del keyword removes the item with the specified key name:

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Example

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The del keyword can also delete the dictionary completely: Bitdefender internet security 2018 key generator.

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Example

The clear() method empties the dictionary:

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Copy a Dictionary

You cannot copy a dictionary simply by typing dict2 = dict1, because: dict2 will only be a reference to dict1, and changes made in dict1 will automatically also be made in dict2.

There are ways to make a copy, one way is to use the built-in Dictionary method copy().

Example

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Make a copy of a dictionary with the copy() method:

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Another way to make a copy is to use the built-in method dict().

Example

Make a copy of a dictionary with the dict() method:

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Nested Dictionaries

A dictionary can also contain many dictionaries, this is called nested dictionaries.

Example

Create a dictionary that contain three dictionaries:

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Or, if you want to nest three dictionaries that already exists as dictionaries:

Example

Create three dictionaries, than create one dictionary that will contain the other three dictionaries:

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The dict() Constructor

It is also possible to use the dict() constructor to make a new dictionary:

Example

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Dictionary Methods

Python has a set of built-in methods that you can use on dictionaries.

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Method	Description
clear()	Removes all the elements from the dictionary
copy()	Returns a copy of the dictionary
fromkeys()	Returns a dictionary with the specified keys and value
get()	Returns the value of the specified key
items()	Returns a list containing a tuple for each key value pair
keys()	Returns a list containing the dictionary's keys
pop()	Removes the element with the specified key
popitem()	Removes the last inserted key-value pair
setdefault()	Returns the value of the specified key. If the key does not exist: insert the key, with the specified value
update()	Updates the dictionary with the specified key-value pairs
values()	Returns a list of all the values in the dictionary