Python Tutorials
Python Introduction
Python Get Started
Python Syntax
Python Comments
Python Variables
Python Data Types
Python Casting
Python Strings
Python Booleans
Python Operators
Python Lists
Python Tuples
Python Sets
Python Dictionaries
Python If...Else
Python While Loops
Python For Loops
Python Functions
Python Lambda
Python Arrays
Python Classes/Objects
Python Inheritance
Python Iterators
Python Scope
Python Modules
Python Dates
Python Math
Python JSON
Python RegEx
Python PIP
Python Try..Except
Python User Input
Python String Formatting
Python File Handling
Python File Handling
Python Read Files
Python Create/Write Files
Python Delete Files
Python Modules
Python Numpy
Python Pandas
Python SciPy
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Python Dictionaries
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
Dictionary
Dictionaries are used to store key data values: value pairs.
The dictionary is a compiled * collection, which is flexible and does not allow duplicates.
From version 3.7 of Python, dictionaries are in order. In Python 3.6 and earlier, dictionaries are not organized.
Dictionaries are written in italics, and have keys and numbers:
Example
Create and print a dictionary:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict)
Dictionary Items
Dictionary items are unique, flexible, and do not allow duplicates.
Dictionary items are presented with a key: in pairs of value, and can be referenced using a keyword.
Example
Print the "brand" value of the dictionary:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(thisdict["brand"])
Ordered or Unordered?
From version 3.7 of Python, dictionaries are in order. In Python 3.6 and earlier, dictionaries are not organized.
If we say that dictionaries are one thing, it means that things are in order, and that order is bound to change.
Disorder means the items do not have a specified order, you cannot refer to an item using the index.
Changeable
Dictionaries are flexible, meaning we can change, add or remove items once the dictionary has been created.
Duplicates Not Allowed
Dictionaries cannot have two objects with the same key:
Example
Duplicate values will overwrite existing values:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964,
"year": 2020
}
print(thisdict)
Dictionary Length
To determine how many items a dictionary contains, use the len() function:
Example
Print the number of items in the dictionary:
print(len(thisdict))
Dictionary Items - Data Items
Prices for dictionary items can be for any type of data:
Example
String, int, boolean, and list data types:
thisdict = {
"brand": "Ford",
"electric": False,
"year": 1964,
"colors": ["red", "white", "blue"]
}
type()
From Python's point of view, dictionaries are defined as 'dictators':
<class 'dict'>
Example
Print the data type of a dictionary:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
print(type(thisdict))
Python Collections (Arrays)
There are four types of data collection in Python editing language:
- The list is a ordered and flexible collection. Allows duplicate members.
- Tuple is a ordered and unchanged collection. Allows duplicate members.
- Set is a random, unstable *, and unidentified collection. No duplicate members.
- The dictionary is a ordered order ** and is flexible. No duplicate members.
* Set items do not change, but you can delete and / or add items whenever you wish.
** Starting with version 3.7 of Python, dictionaries are in order. In Python 3.6 and earlier, dictionaries are not organized.
When choosing a type of collection, it is helpful to understand the characteristics of that type. Choosing the right type of specific data set may mean keeping the definition, and, it may mean increased efficiency or security.
Python - Access Dictionary Items
Accessing Items
You can access dictionary items by referring to its keyword, inside square brackets:
Example
Get the value of the "model" key:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = thisdict["model"]
There is also a method called get () that will give you the same result:
Example
Get the value of the "model" key:
x = thisdict.get("model")
Get Keys
The keys () method will return a list of all the keys to the dictionary.
Example
Get a list of the keys:
x = thisdict.keys()
A list of keywords is a dictionary view, which means that any changes made to the dictionary will be reflected in the key list.
Example
Add a new item to the original dictionary, and see that the keys list gets updated as well:
car = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = car.keys()
print(x) #before the change
car["color"] =
"white"
print(x) #after the change
Get Values
The values () method will return a list of all values to the dictionary.
Example
Get a list of the values:
x = thisdict.values()
The price list is a dictionary view, which means that any changes made to the dictionary will be reflected in the price list.
Example
Make a change in the original dictionary, and see that the values list gets updated as well:
car = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = car.values()
print(x) #before the change
car["year"]
= 2020
print(x) #after the change
Example
Add a new item to the original dictionary, and see that the values list gets updated as well:
car = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = car.values()
print(x) #before the change
car["color"]
= "red"
print(x) #after the change
Get Items
The items () method will return each item to the dictionary, such as tuples in the list.
Example
Get a list of the key:value pairs
x = thisdict.items()
The returned list is a view of dictionary items, which means that any changes made to the dictionary will be reflected in the list of items.
Example
Make a change in the original dictionary, and see that the items list gets updated as well:
car = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = car.items()
print(x) #before the change
car["year"]
= 2020
print(x) #after the change
Example
Add a new item to the original dictionary, and see that the items list gets updated as well:
car = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
x = car.items()
print(x) #before the change
car["color"]
= "red"
print(x) #after the change
Check if Key Exists
To determine if a specific key exists in the dictionary use the internal keyword:
Example
Check if "model" is present in the dictionary:
thisdict = {
"brand": "Ford",
"model": "Mustang",
"year": 1964
}
if "model" in thisdict:
print("Yes, 'model' is
one of the keys in the thisdict dictionary")