Learn Python Dictionaries

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Dictionary

Dictionaries are used to store data values in key:value pairs.

A dictionary is a collection which is ordered*, changeable and do not allow duplicates.
Dictionaries are written with curly brackets, and have keys and values:

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Example-
Create and print a dictionary:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict)

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Dictionary Items

Dictionary items are ordered, changeable, and do not allow duplicates.

Dictionary items are presented in key:value pairs, and can be referred to by using the key name.

Example-
Print the "brand" value of the dictionary:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict["brand"])

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Duplicates Not Allowed

Dictionaries cannot have two items with the same key:

Example-
Duplicate values will overwrite existing values:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964,
"year": 2020
}
print(thisdict)

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Dictionary Length

To determine how many items a dictionary has, use the len() function:

Example-
Print the number of items in the dictionary:

print(len(thisdict))

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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:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict["year"] = 2018

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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-
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict["color"] = "red"
print(thisdict)

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Update Dictionary

The update() method will update the dictionary with the items from a given argument. If the item does not exist, the item will be added.

The argument must be a dictionary, or an iterable object with key:value pairs.

Example-
Add a color item to the dictionary by using the update() method:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict.update({"color": "red"})

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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:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict.pop("model")
print(thisdict)

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

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
del thisdict["model"]
print(thisdict)

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Example-
The clear() method empties the dictionary:

thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
thisdict.clear()
print(thisdict)

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