Python add element to dictionary

Python Add to Dictionary – Adding an Item to a Dict

Ihechikara Vincent Abba

Data structures help us organize and store collections of data. Python has built-in data structures like Lists, Sets, Tuples and Dictionaries.

Each of these structures have their own syntax and methods for interacting with the data stored.

In this article, we’ll talk about Dictionaries, their features, and how to add items to them.

How to Create a Dictionary in Python

Dictionaries are made up of key and value pairs nested in curly brackets. Here’s an example of a Dictionary:

In the code above, we created a dictionary called devBio with information about a developer – the developer’s age is quite overwhelming.

Each key in the dictionary – name , age and language – has a corresponding value. A comma separates each key and value pair from another. Omitting the comma throws an error your way.

Before we dive into how we can add items to our dictionaries, let’s have a look at some of the features of a dictionary. This will help you easily distinguish them from other data structures in Python.

Features of a Dictionary

Here are some of the features of a dictionary in Python:

Duplicate Keys Are Not Allowed

If we create a dictionary that has two or multiple identical keys in it, the last key out of them will override the rest. Here’s an example:

We created three keys with an identical key name of name . When we printed our dictionary to the console, the last key having a value of «Chikara» overwrote the rest.

Let’s see the next feature.

Items in a Dictionary Are Changeable

After assigning an item to a dictionary, you can change its value to something different.

devBio = < "name": "Ihechikara", "age": 120, "language": "JavaScript" >devBio["age"] = 1 print(devBio) #

In the example above, we reassigned a new value to age . This will override the initial value we assigned when the dictionary was created.

We can also use the update() method to change the value of items in our dictionary. We can achieve the same result in the last example by using the update() method – that is: devBio.update() .

Items in a Dictionary Are Ordered

By being ordered, this means that the items in a dictionary maintain the order in which they were created or added. That order cannot change.

Prior to Python 3.7, dictionaries in Python were unordered.

In the next section, we will see how we can add items to a dictionary.

How to Add an Item to a Dictionary

The syntax for adding items to a dictionary is the same as the syntax we used when updating an item. The only difference here is that the index key will include the name of the new key to be created and its corresponding value.

Here’s what the syntax looks like: devBio[newKey] = newValue .

We can also use the update() method to add new items to a dictionary. Here’s what that would look like: devBio.update(newKey«: newValue>) .

devBio = < "name": "Ihechikara", "age": 120, "language": "JavaScript" >devBio["role"] = "Developer" print(devBio) #

Above, using the index key devBio[«role»] , we created a new key with the value of Developer .

In the next example, we will use the update() method.

devBio = < "name": "Ihechikara", "age": 120, "language": "JavaScript" >devBio.update() print(devBio) #

Above, we achieved the same result as in the last example by passing in the new key and its value into the update() method – that is: devBio.update() .

Conclusion

In this article, we learned what dictionaries are in Python, how to create them, and some of their features. We then saw two ways through which we can add items to our dictionaries.

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Python: How to Add Items to Dictionary

Dictionaries are Python’s built-in data types for storing key-value pairs. The dictionary elements are changeable and don’t allow duplicates. In Python 3.7 and higher, dictionary items are ordered. Lower versions of Python treat dictionary elements as unordered.

Depending on the desired result and given data, there are various ways to add items to a dictionary.

This guide shows how to add items to a Python dictionary through examples.

• Python version 3.7 or higher.
• A text editor or IDE to write code.
• A method to run the code, such as a terminal or IDE.

How to Add an Item to a Dictionary in Python

To test out different methods of adding items to a dictionary, create a dictionary with two items. Use the following code:

The methods below show how to add one or multiple items to a Python dictionary.

Note: Adding an item with an existing key replaces the dictionary item with a new value. Make sure to provide unique keys to avoid overwriting data.

Method 1: Using The Assignment Operator

The assignment operator sets a value to a key using the following syntax:

dictionary_namePython add element to dictionary = value

The assignment operator adds a new key-value pair if the key does not exist.

The following code demonstrates how to add an item to a Python dictionary using the assignment operator:

my_dictionary = < "one": 1, "two": 2 >print("Before:", my_dictionary) my_dictionary["tree"] = 3 print("After:", my_dictionary)

The code outputs the dictionary contents before and after adding a new item.

Method 2: Using update()

The update() method updates an existing dictionary with a new dictionary item:

The method accepts one or multiple key-value pairs, which is convenient for adding more than one element.

The example code looks like the following:

my_dictionary = < "one": 1, "two": 2 >print("Before:", my_dictionary) my_dictionary.update() print("After:", my_dictionary)

Use this method to add multiple new items or append a dictionary to an existing one.

Method 3: Using __setitem__

The __setitem__ method is another way to append a new dictionary item:

dictionary_name.__setitem__(key,value)

my_dictionary = < "one": 1, "two": 2 >print("Before:", my_dictionary) my_dictionary.__setitem__("three", 3) print("After:", my_dictionary)

The method sets the item key as «three» with the value 3 .

Method 4: Using The ** Operator

The ** operator helps merge an existing dictionary into a new dictionary and adds additional items. The syntax is:

For example, to copy an existing dictionary and append a new item to a new one, see the following code:

my_dictionary = < "one": 1, "two": 2 >my_new_dictionary = <**my_dictionary, **<"three":3>> print("Old:", my_dictionary) print("New:", my_new_dictionary)

The new dictionary contains the added item, preserving the old dictionary values. Use this method to avoid changing existing dictionaries.

Method 5: Checking If A Key Exists

Use an if statement to check whether a key exists before adding a new item to a dictionary. The example syntax is:

if key not in dictionary_name: dictionary_namePython add element to dictionary = value

my_dictionary = < "one": 1, "two": 2 >print("Before:", my_dictionary) if "three" not in my_dictionary: my_dictionary["three"] = 3 print("After:", my_dictionary)

The code checks whether a key with the provided name exists before adding the item to the dictionary. If the provided key exists, the existing key value does not update, and the dictionary stays unchanged.

Method 6: Using A For Loop

Add key-value pairs to a nested list and loop through the list to add multiple items to a dictionary. For example:

my_dictionary = < "one": 1, "two": 2 >my_list = [["three", 3], ["four", 4]] print("Before:", my_dictionary) for key,value in my_list: my_dictionaryPython add element to dictionary = value print("After:", my_dictionary)

The for loop goes through the pairs inside the list and adds two new elements.

Note: For loop and a counter are also used as one of the methods to identify the length of a list. Learn more by visiting our guide How to Find the List Length in Python.

Method 7: Using zip

Use zip to create key-value pairs from two lists. The first list contains keys and the second contains the values.

my_dictionary = < "one": 1, "two": 2 >my_keys = ["three", "four"] my_values = [3, 4] print("Before:", my_dictionary) for key,value in zip(my_keys, my_values): my_dictionaryPython add element to dictionary = value print("After:", my_dictionary)

The zip function matches elements from two lists by index, creating key-value pairs.

How to Update a Python Dictionary

Update Python dictionary values using the same syntax as adding a new element. Provide the key name of an existing key, for example:

my_dictionary = < "one": 1, "two": 2 >print("Before:", my_dictionary) my_dictionary["one"] = 3 print("After:", my_dictionary)

Since Python does not allow duplicate entries in a dictionary, the code updates the value for the provided key and overwrites the existing information.

After going through the examples in this tutorial, you know how to add items to a Python dictionary. All methods provide unique functionalities, so choose a way that best suits your program and situation.

For more Python tutorial refer to our article and find out how to pretty print a JSON file using Python.

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Adding to Dict in Python – How to Append to a Dictionary

Shittu Olumide

A dictionary in Python is a group of unordered items, each of which has a unique set of keys and values.

Any immutable data type, such as a string, number, or tuple, can be used as the key. It serves as an exclusive identifier for the value in the dictionary. The value is repeatable and applicable to all types of data.

In Python, dictionaries are denoted by curly braces < >, and each key-value pair is delimited by a colon : . A comma separates the key and value. Here is an illustration of a basic dictionary:

In this example, «pineapple», «apple», «orange», and «avocado» are the keys, and 12, 30, 5 and 7 are the corresponding values.

We will have a look at how we can add a single key-value pair to a dictionary using the update() method, and finally the dict() constructor.

How to add a single key-value pair to a dictionary

To add a single key-value pair to a dictionary in Python, we can use the following code:

The above code will create a dictionary myDict with two key-value pairs. Then we added a new key-value pair ‘c’ : 3 to the dictionary by just assigning the value 3 to the key ‘c’ . After the code is executed, the dictionary myDict will now contain the key-value pair ‘c’: 3 .

Let’s confirm this by printing the dictionary.

If there is a key ‘c’ in the dictionary already, the value would be updated to 3.

How to add multiple key-value pairs with the update() method

Multiple key-value pairs can be simultaneously added to a dictionary using the update() method. This method inserts new entries into the original dictionary from another dictionary or an iterable of key-value pairs as input. The value of an existing key in the original dictionary will be updated with the new value.

Example using the update() method to add multiple entries to a dictionary:

myDict = new_data = myDict.update(new_data) print(myDict) 

Another fun thing about this method is that, we can use the update() method with an iterable of key-value pairs, such as a list of tuples. Let’s see this in action.

myDict = new_data = [('c', 3), ('d', 4)] myDict.update(new_data) print(myDict) 

The output is the same as the previous example:

How to update a dictionary using the dict() constructor

In Python, a dictionary can be updated or made from scratch using the dict() constructor. By passing a dictionary containing the new key-value pair as an argument to the dict() constructor, we can add a single key-value pair to an existing dictionary.

myDict = newDict = dict(myDict, d=4) print(newDict) 

In this example, three key-value pairs were added to a brand-new dictionary called myDict . Then, we created a new dictionary called newDict using the dict() constructor, which also added the key-value pair ‘d’: 4′ .

When the two dictionaries are combined by the dict() constructor, any keys that are present in both dictionaries have their values overwritten by the value from the second dictionary (in this case, ‘d’: 4′ ).

Keep in mind that a new dictionary can also be created using the dict() constructor from a list of key-value pairs, where each pair is represented by a tuple.

MyList = [('a', 1), ('b', 2), ('c', 3)] MyDict = dict(MyList) print(MyDict) 

Conclusion

In Python, dictionaries are frequently used to store data and provide quick access to it using a distinct key value. They come in handy when working with lists or tuples, where we need to access data using a specific identifier rather than its place in a sequence.

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