• Generate dictionaries for iterable structures.
  • Very similar to list comprehensions.
  • An example is a list of tuoles that we will be using as our key value pairs.
    • Tuples work just like lists, however you cannot alter the value of Tuples once they have been declared. 
      animalList = [('a', 'aardvark'), ('b', 'bear'), ('c', 'cat'), ('d', 'dog')]
animals = {item[0]: item[1] for item in animalList}
animals
  • This will output the following: 
    {'a': 'aardvark', 'b': 'bear', 'c': 'cat', 'd': 'dog'}
  • Need to define the key and value, separated by a colon.
  • There is a much nicer way to write the above statement as well. 
    animals = {key: value for key, value in animalList}
animals
  • That will output the same thing: 
    {'a': 'aardvark', 'b': 'bear', 'c': 'cat', 'd': 'dog'}
  • Whatever is between the for and in of this statement, is what each Tuple of animalList is being assigned to.
  • Python allows you to unpack values into multiple variables, as long as the number of variables you are assigning values to matches the elements in the data structure.
  • We are unpacking the above items into pairs of value variables.
  • What if we want to take the animal dictionary and turn it back into a list.
    • We can use the items function.
  • animals.items() will return: 
    dict_items([('a', 'aardvark'), ('b', 'bear'), ('c', 'cat'), ('d', 'dog')])
  • Can turn it back into the original animal list as above with: 
    list(animals.items())
  • Will output: 
    [('a', 'aardvark'), ('b', 'bear'), ('c', 'cat'), ('d', 'dog')]
  • What if we want each item to have a structure different:
    • We can use a list comprehension. 
      [{'letter': key, 'name': value} for key, value in animals.items()]
  • That will output: 
    [{'letter': 'a', 'name': 'aardvark'}],
{'letter': 'b', 'name': 'bear'},
{'letter': 'c', 'name': 'cat'},
{'letter': 'd', 'name': 'dog'},
  • Very powerful to process and format data in Python.

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