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Organizing data with dictionaries

From: Python 3 Essential Training

Video: Organizing data with dictionaries

Dictionaries are Python's version of associative arrays or hashed arrays. Dictionaries are created in a couple of different ways. We can create a dictionary with the curly braces and we can say key value like this. So now, we have a dictionary with those values in it. Actually, an easier way to create dictionaries is with its constructor because this allows you to use the named parameters feature of Python and it's just a whole lot easier to type.

Organizing data with dictionaries

Dictionaries are Python's version of associative arrays or hashed arrays. Dictionaries are created in a couple of different ways. We can create a dictionary with the curly braces and we can say key value like this. So now, we have a dictionary with those values in it. Actually, an easier way to create dictionaries is with its constructor because this allows you to use the named parameters feature of Python and it's just a whole lot easier to type. So you will see it done this way more often.

We get exactly the same result and see that that type is a class dictionary. Finally, if you want to, you can even initialize one dictionary from another. If I have another dictionary? And so there I have that dictionary. I can say d = dictionary and I can take these definitions from up here, copy those and paste those in, and then I can actually specify that other dictionary with the two asterisk notation and I get a dictionary that has all of that in it.

You can test if a value is in a dictionary by saying 'four' in x and I see that that's True and if I say 'three' in x that will not be true, because x here has just four, five and six in it. Likewise, you can iterate over a dictionary. You can say four k in d: print (k) and that will print out all of the keys. If you want to, you can say for k key and value in d.items print k and value.

And that will give you both the keys and the values all in one fell swoop. If you want to find a particular item in a dictionary, one way to do it is to simply subscript it. The problem with that is that if your dictionary does not have that key, you will get an exception. If I try x sub 'three', I will get an exception. The way around that is to use the get method. If I say x.get('three'), it will simply silently give me the none value.

If I say d.get('three') then I get the value. Another benefit of this is using the get method I can give it a default value. I can say give me that value of three or give me some default value. And I get the default value. Here I typed in the text 'not found'. If I simply want to delete an item from a dictionary, I can just look at the x here. I've got those items there. I can say del x' sub four' and now that's gone or I can say x.pop('five') and it will give me the value and delete it at the same time.

So those are the major functions of dictionaries. Dictionaries are tremendously useful. Whenever you need to organize your data in such a way that it's easy to find, you can certainly store any kind of data in a list or in a tuple. But the indexes are always going to be numeric. The advantage of the dictionaries is that the indexes are data. So you can index it on any kind of data. Usually, you will use text, usually you will use words, but this allows you to basically create your own named spaces and organize them.

They can be hierarchical. You can store dictionaries within dictionaries, you can store lists and tuples within dictionaries, and you will find as you will look through the examples of the code that I have written, I will often times carry one dictionary in a global namespace and put all of my data inside of that and then it becomes manageable. It's like a halfway point between flat data and an object with methods. Obviously, there is going to be times you are going to want to create an object with methods to handle your data in very specific ways, but for just organizing a whole lot of global variables or flags, you will find that dictionaries are very useful and for organizing object data within an object, you will find that dictionaries are very, very useful and very, very commonly used in these kinds of situations.

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This video is part of

Image for Python 3 Essential Training
Python 3 Essential Training

87 video lessons · 40765 viewers

Bill Weinman
Author

 
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  1. 5m 14s
    1. Welcome
      1m 32s
    2. Understanding prerequisites for Python
      2m 4s
    3. Using the exercise files
      1m 38s
  2. 33m 29s
    1. Getting started with "Hello World"
      4m 43s
    2. Selecting code with conditionals
      4m 45s
    3. Repeating code with a loop
      4m 13s
    4. Reusing code with a function
      2m 43s
    5. Creating sequences with generator functions
      2m 46s
    6. Reusing code and data with a class
      4m 39s
    7. Greater reusability with inheritance and polymorphism
      7m 17s
    8. Handling errors with exceptions
      2m 23s
  3. 22m 32s
    1. Installing Python 3 and Eclipse for Windows
      11m 24s
    2. Installing Python 3 and Eclipse for Mac
      11m 8s
  4. 28m 0s
    1. Creating a main script
      3m 27s
    2. Understanding whitespace in Python
      4m 8s
    3. Commenting code
      3m 28s
    4. Assigning values
      3m 37s
    5. Selecting code and values with conditionals
      4m 46s
    6. Creating and using functions
      3m 54s
    7. Creating and using objects
      4m 40s
  5. 31m 23s
    1. Understanding variables and objects in Python
      2m 46s
    2. Distinguishing mutable and immutable objects
      2m 41s
    3. Using numbers
      3m 34s
    4. Using strings
      6m 38s
    5. Aggregating values with lists and tuples
      4m 55s
    6. Creating associative lists with dictionaries
      4m 24s
    7. Finding the type and identity of a variable
      4m 45s
    8. Specifying logical values with True and False
      1m 40s
  6. 9m 42s
    1. Selecting code with if and else conditional statements
      2m 22s
    2. Setting multiple choices with elif
      2m 14s
    3. Understanding other strategies for multiple choices
      2m 38s
    4. Using the conditional expression
      2m 28s
  7. 11m 26s
    1. Creating loops with while
      1m 27s
    2. Iterating with for
      3m 54s
    3. Enumerating iterators
      3m 22s
    4. Controlling loop flow with break, continue, and else
      2m 43s
  8. 23m 28s
    1. Performing simple arithmetic
      2m 14s
    2. Operating on bitwise values
      3m 30s
    3. Comparing values
      3m 32s
    4. Operating on Boolean values
      2m 59s
    5. Operating on parts of a container with the slice operator
      6m 52s
    6. Understanding operator precedence
      4m 21s
  9. 11m 34s
    1. Using the re module
      1m 4s
    2. Searching with regular expressions
      3m 12s
    3. Replacing with regular expressions
      3m 29s
    4. Reusing regular expressions with re.compile
      3m 49s
  10. 9m 10s
    1. Learning how exceptions work
      1m 18s
    2. Handling exceptions
      4m 15s
    3. Raising exceptions
      3m 37s
  11. 23m 1s
    1. Defining functions
      6m 23s
    2. Using lists of arguments
      2m 26s
    3. Using named function arguments
      4m 32s
    4. Returning values from functions
      1m 55s
    5. Creating a sequence with a generator function
      7m 45s
  12. 47m 29s
    1. Understanding classes and objects
      5m 12s
    2. Using methods
      6m 12s
    3. Using object data
      10m 4s
    4. Understanding inheritance
      5m 11s
    5. Applying polymorphism to classes
      7m 13s
    6. Using generators
      9m 48s
    7. Using decorators
      3m 49s
  13. 18m 54s
    1. Understanding strings as objects
      3m 25s
    2. Working with common string methods
      5m 24s
    3. Formatting strings with str.format
      5m 31s
    4. Splitting and joining strings
      2m 49s
    5. Finding and using standard string methods
      1m 45s
  14. 25m 27s
    1. Creating sequences with tuples and lists
      4m 6s
    2. Operating on sequences with built-in methods
      5m 50s
    3. Organizing data with dictionaries
      4m 56s
    4. Operating on character data with bytes and byte arrays
      10m 35s
  15. 11m 46s
    1. Opening files
      2m 4s
    2. Reading and writing text files
      4m 33s
    3. Reading and writing binary files
      5m 9s
  16. 21m 27s
    1. Creating a database with SQLite 3
      6m 56s
    2. Creating, retrieving, updating, and deleting records
      7m 31s
    3. Creating a database object
      7m 0s
  17. 18m 27s
    1. Using standard library modules
      8m 0s
    2. Finding third-party modules
      5m 47s
    3. Creating a module
      4m 40s
  18. 23m 11s
    1. Dealing with syntax errors
      8m 19s
    2. Dealing with runtime errors
      4m 0s
    3. Dealing with logical errors
      4m 22s
    4. Using unit tests
      6m 30s
  19. 19m 56s
    1. Normalizing a database interface
      6m 39s
    2. Deconstructing a database application
      8m 9s
    3. Displaying random entries from a database
      5m 8s
  20. 29s
    1. Goodbye
      29s

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