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

A Python dictionary is like a JavaScript object – it’s a sequence of key:value pairs. So, you can create them like this:

stack_dict = {
    "frontend": "JavaScript",
    "backend": "Node JS",
    "markup": "HTML and JSX",
}

To access the value in the dictionary, you can do it this way: dict[key]. For example, if I want to access what the frontend key holds, I can do it like this:

print(stack_dict["frontend"])
# JavaScript

But what if you want to add another entry to the dictionary without going back to the dictionary to put it there? That's what we are going to look at in this article. And I'm going to show you how to do it in 3 different ways.

What We'll Cover

• How to Add to a Dictionary in Python
• How to Add to a Dictionary by Mapping a key to the Dictionary
• How to Add to a Dictionary by Using the update() Method
• How to Add to a Dictionary by Using the if Statement
• Conclusion

How to Add to a Dictionary in Python

You can add to a dictionary in three different ways:

• map a key to the dictionary
• use the update() method
• use an if statement

How to Add to a Dictionary in Python by Mapping a key to the Dictionary

If you want to add to a dictionary with this method, you'll need to add the value with the assignment operator.

dict["key"] = "value"`

This would also override the value of an existing key.

In the stack dictionary I defined earlier, there's no styling there:

stack_dict = {
    "frontend": "JavaScript",
    "backend": "Node JS",
    "markup": "HTML and JSX",
}

So let's add a styling key and CSS value to the dictionary by mapping a new key to the dictionary:

stack_dict["styling"] = "CSS"

print(stack_dict)
# Output: {'frontend': 'JavaScript', 'backend': 'Node JS', 'markup': 'HTML and JSX', 'styling': 'CSS'}

You can see that a new key of styling and a value of CSS has been added to the dictionary.

If the key already exists, the value gets overwritten:

stack_dict["markup"] = "HTML only"
print(stack_dict)

# {'frontend': 'JavaScript', 'backend': 'Node JS', 'markup': 'HTML only'}

How to Add to a Dictionary in Python Using the update() Method

The stack is still missing a JavaScript library, so let's add it with the update() method. You can do that this way:

dict.update({"key": "value"})`.

So, to add the JavaScript framework/library, I did it like this:

stack_dict.update({"JS Framework": "React/Next"})

print(stack_dict)
# {'frontend': 'JavaScript', 'backend': 'Node JS', 'markup': 'HTML and JSX', 'styling': 'CSS', 'JS Framework': 'React/Next'}

The update() also overwrites an existing value if it's different:

stack_dict.update({"backend": "Django"})

print(stack_dict)
# {'frontend': 'JavaScript', 'backend': 'Django', 'markup': 'HTML and JSX'}

How to Add to a Dictionary in Python Using the if Statement

If you don't want an entry to be overwritten even if it already exists, you can use an if statement. You can do it with this syntax:

if "value" not it dict.keys():
    dict["key"] = "value"

I want to add a "CSS Framework" key with a value of "Tailwind CSS" to the stack dictionary, so I'm going to do that with the help of this syntax:

if "Tailwind CSS" not in stack_dict.keys():
    stack_dict["CSS Framework"] = "Tailwind CSS"

print(stack_dict)
# {'frontend': 'JavaScript', 'backend': 'Node JS', 'markup': 'HTML and JSX', 'styling': 'CSS', 'JS Framework': 'React/Next', 'CSS Framework': 'Tailwind CSS'}

If the entry is already in the dictionary, it won't be added in there:

if "HTML and JSX" not in stack_dict.keys():
    stack_dict["markup"] = "HTML and JSX"

print(stack_dict)
# {'frontend': 'JavaScript', 'backend': 'Node JS', 'markup': 'HTML and JSX', 'styling': 'CSS', 'JS Framework': 'React/Next'}

If you don't feel like using an if statement to add to the dictionary, you can do the same thing with try…except…:

try:
  stack_dict["Deployment"] = "Anywhere possible"
except:
  print("An exception occurred")

print(stack_dict)
# {'frontend': 'JavaScript', 'backend': 'Node JS', 'markup': 'HTML and JSX', 'styling': 'CSS', 'JS Framework': 'React/Next', 'Deployment': 'Anywhere possible'}

Conclusion

This article took you through three different ways to add to a dictionary in Python:

• mapping a key to the dictionary
• using the update() method
• using an if statement

We even looked at how you can add to a dictionary with the try…except… expression.

Thank you for reading.