Dictionaries.py

# Python Dictionaries
thisdict = {
  "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 are ordered. In Python 3.6 and earlier, dictionaries are unordered.

# Dictionaries are written with curly brackets, and have keys and values:

# Example
# Create and print a dictionary:

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

# Dictionary Items
# Dictionary items are ordered, changeable, and does 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"])

# Ordered or Unordered?
# As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

# 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 does 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:

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

# 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))

# Dictionary Items - Data Types
# The values in dictionary items can be of any data type:

# Example
# String, int, boolean, and list data types:

thisdict = {
  "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':

# <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 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.
# *Set items are unchangeable, but you can remove and/or add items whenever you like.

# **As of Python version 3.7, dictionaries are ordered. In Python 3.6 and earlier, dictionaries are unordered.

# 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.

# Python has a set of built-in methods that you can use on dictionaries.

# Method	          Description
# clear()	          Removes all the elements from the dictionary
# copy()	          Returns a copy of the dictionary
# fromkeys()	      Returns a dictionary with the specified keys and value
# get()	            Returns the value of the specified key
# items()	          Returns a list containing a tuple for each key value pair
# keys()	          Returns a list containing the dictionary's keys
# pop()	            Removes the element with the specified key
# popitem()	        Removes the last inserted key-value pair
# setdefault()	    Returns the value of the specified key. 
#                   If the key does not exist: insert the key, with the specified value
# update()	        Updates the dictionary with the specified key-value pairs
# values()	        Returns a list of all the values in the dictionary