Can we replace key in dictionary python?

Question

Table of Contents Show

Swap values
How to Create a Dictionary?
How to Add a Key:Value Pair to a Dictionary?
How to Replace a Key in a Dictionary?
How to Replace a Value in a Dictionary?
How to Retrieve a Value associated with a Key?
How to Remove a Key:Value Pair in a Dictionary?
Can we change keys in dictionary Python?
Can I change a value in a dictionary Python?
How do you set a key value in Python?
Can we update the value of a key in dictionary?
Are Keys in dictionary replaceable?
Can I swap keys and values in dictionary Python?
Can you modify dictionary in Python?
Can I swap keys and values in dictionary Python?
How do you rename a key in a dictionary?
Can a dictionary key be duplicated?
Can the keys in dictionary Python be same?

Table of Contents

Swap values
How to Create a Dictionary?
How to Add a Key:Value Pair to a Dictionary?
How to Replace a Key in a Dictionary?
How to Replace a Value in a Dictionary?
How to Retrieve a Value associated with a Key?
How to Remove a Key:Value Pair in a Dictionary?
Can we change keys in dictionary Python?
Can I change a value in a dictionary Python?
How do you set a key value in Python?
Can we update the value of a key in dictionary?
Are Keys in dictionary replaceable?
Can I swap keys and values in dictionary Python?
Can you modify dictionary in Python?

Table of Contents

Swap values
How to Create a Dictionary?
How to Add a Key:Value Pair to a Dictionary?
How to Replace a Key in a Dictionary?
How to Replace a Value in a Dictionary?
How to Retrieve a Value associated with a Key?
How to Remove a Key:Value Pair in a Dictionary?
Can we change keys in dictionary Python?
Can I change a value in a dictionary Python?
How do you set a key value in Python?
Can we update the value of a key in dictionary?

A dictionary is a one to one mapping. Every key has a value.
In Python that can be

dict = {'a': 1, 'b': 2, 'c': 3}

You can then get the values like this

That's great and all. But what if you want to flip the entire dictionary? Where keys are values and values and keys.

Swap values

You can easily swap the key,dictionary pairs in Python, with a one liner.

dict = {value:key for key, value in dict.items()}

So in practice you can have something like this:

dict = {'a': 1, 'b': 2, 'c': 3}
print(dict)

dict = {value:key for key, value in dict.items()}
print(dict)

This will output

{'a': 1, 'c': 3, 'b': 2}
{1: 'a', 2: 'b', 3: 'c'}

So the one liner

dict = {value:key for key, value in dict.items()}

flipped the whole dictionary. Nice trick :)

Learn Python?

https://pythonbasics.org/
https://pythonprogramminglanguage.com/

Python defines the dictionary data type as an unordered collection that contains key:value pairs. The key:value pairs (separated by commas) are wrapped inside curly braces ({}).

Each key inside the dictionary must be unique and immutable. Dictionary keys can be one of the following data types: integer, string, or tuple. Dictionary keys can not be a list as lists are mutable. Values can be of any data type and do not need to be unique.

Python Dictionary – The Ultimate Guide

How to Create a Dictionary?
How to Add a Key:Value Pair to a Dictionary?
How to Replace a Key in a Dictionary?
How to Replace a Value in a Dictionary?
How to Retrieve a Value associated with a Key?
How to Remove a Key:Value Pair in a Dictionary?

How to Create a Dictionary?

Python has two ways to create/initialize an empty dictionary object. One option is to use curly braces ({}). The other is to use the built-in dict() constructor method. For this tutorial, the curly braces({}) option will be referenced.

composers = {}
composers = dict()

You may want to create a dictionary and initialize it with key:value data in some instances. The example below is a small representation of classical composers and their respective birth years.

Dictionaries can handle various data types (outlined above) inside the same structure. For example, if we added a key (integer 2) and assigned this key a value (string 'test'), the dictionary would be updated with no errors. However, we recommend that for clarity, the initial structure design remains intact.

composers = {'Chopin':  1810,
             'Greeg':   1843,
             'Handel': 1684,
             'Mozart': 1756
            }

How to Add a Key:Value Pair to a Dictionary?

To add a new key:value pair to a dictionary, add a key inside the square brackets at the end of the dictionary reference. Assign this key a value using the equals (=) sign.

The code below adds the composer Bach and his birth year and displays the output.

composers['Bach'] = 1685
print(composers)

Output

{'Chopin': 1810, 'Greeg': 1843, 'Handel': 1684, 
 'Mozart': 1756, 'Bach': 1685}

How to Replace a Key in a Dictionary?

Use the method to replace a key in an existing key:value pair. For example, this method updates an existing dictionary key with a new key.

In the dictionary composers created earlier, the spelling of Grieg (Greeg) contained a typing error. After running this code, the key reflects the correct name in the output below.

composers['Grieg'] = composers.pop('Greeg')
print(composers)

Output

{'Chopin': 1810, 'Handel': 1684, 'Mozart': 1756, 
 'Bach': 1732, 'Grieg': 1843}

How to Replace a Value in a Dictionary?

To replace a value in an existing key:value pair, assign the key to be replaced inside the square brackets at the end of the dictionary reference. Then, assign a different value using the equals sign (=).

The code below changes the incorrect birth year for the composer Handel.

composers['Handel'] = 1685
print(composers)

Output

{'Chopin': 1810, 'Handel': 1685, 'Mozart': 1756, 
 'Bach': 1732, 'Grieg': 1843}

How to Retrieve a Value associated with a Key?

To retrieve a value associated with a specific existing dictionary key, create a variable (x) and assign this variable to the appropriate key. If the key does not exist, an error will occur. The value of x (the birth year of Chopin) is displayed.

x = composers['Chopin']
print(composers)

Output

How to Remove a Key:Value Pair in a Dictionary?

To remove an unwanted dictionary key:value pair, use the pop() method. The parameter inside pop() must be an existing dictionary key, or an error will occur. The output displays the modified dictionary with the composer Mozart removed.

composers.pop('Mozart')
print(composers)

Output

{'Chopin': 1810, 'Handel': 1685, 
 'Bach': 1732, 'Grieg': 1843}

To learn more about basic Python skills, feel free to check out our free cheat sheets and email academy:

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During the past 15 years, I have held a number of positions such as:

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Can we change keys in dictionary Python?

Since keys are what dictionaries use to lookup values, you can't really change them. The closest thing you can do is to save the value associated with the old key, delete it, then add a new entry with the replacement key and the saved value.

Can I change a value in a dictionary Python?

Assign a new value to an existing key to change the value Use the format dict[key] = value to assign a new value to an existing key.

How do you set a key value in Python?

Below are the two approaches which we can use..

Assigning a new key as subscript. We add a new element to the dictionary by using a new key as a subscript and assigning it a value. ... .

Using the update() method. ... .

By merging two dictionaries..

Can we update the value of a key in dictionary?

Note: The update() method adds element(s) to the dictionary if the key is not in the dictionary. If the key is in the dictionary, it updates the key with the new value.

Are Keys in dictionary replaceable?

Keys in a dictionary can only be used once. If it is used more than once, as you saw earlier, it'll simply replace the value. 00:19 A key must be immutable—that is, unable to be changed. These are things like integers, floats, strings, Booleans, functions.

Can I swap keys and values in dictionary Python?

You can swap keys and values in a dictionary with dictionary comprehensions and the items() method.

Can you modify dictionary in Python?

At some point you may want to modify one of the values in your dictionary. Modifying a value in a dictionary is pretty similar to modifying an element in a list. You give the name of the dictionary and then the key in square brackets, and set that equal to the new value.

Can I swap keys and values in dictionary Python?

You can swap keys and values in a dictionary with dictionary comprehensions and the items() method.

How do you rename a key in a dictionary?

How to rename a key in a Python dictionary? To rename a Python dictionary key, use the dictionary pop() function to remove the old key from the dictionary and return its value. And then add the new key with the same value to the dictionary.