PythonDictionaries
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
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.
As of Python version 3.7, dictionaries areordered. In Python 3.6 and earlier, dictionaries areunordered.
Dictionaries are written with curly brackets, and have keys and values:
Example
Create and print a dictionary:
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict)
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:
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict["brand"])
Ordered or Unordered?
As of Python version 3.7, dictionaries areordered. In Python 3.6 and earlier, dictionaries areunordered.
When we say that dictionaries are ordered, it means that the items have a defined order, and that order will not change.
Unordered means that the items do not have a defined order, you cannot refer to an item by using an index.
Changeable
Dictionaries are changeable, meaning that we can change, add or remove items after the dictionary has been created.
Duplicates Not Allowed
Dictionaries cannot have two items with the same key:
Example
Duplicate values will overwrite existing values:
"brand": "Ford",
"model": "Mustang",
"year": 1964,
"year": 2020
}
print(thisdict)
Dictionary Length
To determine how many items a dictionary has, use thelen() function:
Dictionary Items - Data Types
The values in dictionary items can be of any data type:
Example
String, int, boolean, and list data types:
"brand": "Ford",
"electric": False,
"year": 1964,
"colors": ["red", "white", "blue"]
}
type()
From Python's perspective, dictionaries are defined as objects with the data type 'dict':
Example
Print the data type of a dictionary:
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(type(thisdict))
The dict() Constructor
It is also possible to use thedict() constructor to make a dictionary.
Example
Using the dict() method to make a dictionary:
print(thisdict)
Python Collections (Arrays)
There are four collection data types in the Python programming language:
- List is a collection which is ordered and changeable. Allows duplicate members.
- Tuple is a collection which is ordered and unchangeable. Allows duplicate members.
- Set is a collection which is unordered, unchangeable*, and unindexed. No duplicate members.
- Dictionary is a collection which is ordered** and changeable. No duplicate members.
*Setitems are unchangeable, but you can remove and/or add items whenever you like.
**As of Python version 3.7, dictionaries areordered. In Python 3.6 and earlier, dictionaries areunordered.
When choosing a collection type, it is useful to understand the properties of that type. Choosing the right type for a particular data set could mean retention of meaning, and, it could mean an increase in efficiency or security.
