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Creating a module

From: Python 3 Essential Training

Video: Creating a module

Oftentimes as you are writing code you'll find pieces of code that you want to reuse in different projects. For this you'll want to write here own modules. So let's take a look at how we do this. For example, if this is my homepage and if you look down at the bottom of the page you'll see that it tells the time and it says it in words. It says it's twenty past three. Now, I did this with a Python module, and we're going to take a look at that module, and here it is. Now, the point of this is to show you how to put the code into the module.

Creating a module

Oftentimes as you are writing code you'll find pieces of code that you want to reuse in different projects. For this you'll want to write here own modules. So let's take a look at how we do this. For example, if this is my homepage and if you look down at the bottom of the page you'll see that it tells the time and it says it in words. It says it's twenty past three. Now, I did this with a Python module, and we're going to take a look at that module, and here it is. Now, the point of this is to show you how to put the code into the module.

We'll look at the details of the module in another lesson. But for now let's see that it has this class numwords. But for now let's just look at from the perspective of how we put the code into a module. So you'll notice that it has this class numwords, and this formats a number into words. And it has this other class saytime_t that inherits numwords and that class is for formatting the time as words.

And then it has a special version of saytime as a wrapper for using a time object. And it has a main function, so that it can be run from the command line. And it has a test function for testing. And so all of this is put in a normal file and really there is nothing special about the file. In fact, if I run it-- we'll go ahead and do that. You see that it gives the time right now, twenty-eight til five.

It can also be run with an argument that hasn't run these tests. And in Eclipse, so a little bit of a production to get it to do that, to come over here and give it an argument, say test, and Apply and Run, and then it runs it in test mode. And you'll see if I do that from the command line, I just give the word test on the command line, and it runs all of these tests. It tests all the numbers and it tests the time.

I'd like to do things this way. You can also use the unit testing module that comes with Python. And so I have a lot of results that I could look at. So the module itself you just write it like you write a normal script. You write your script and in the process you write whatever classes you're going to write. And you think about how it will be accessible from the outside world. And then when it's time to use it as a module you'll notice down here at the bottom it has this if _name_ pattern, we've seen this before.

And that prevents the main code from being run when it's imported as a module. So I don't have any code that's outside of a function. And that's generally true when I write a script any way. And here is the script on my web site. It's a very short script. That's the entire thing. And all it does is it imports time, because it grabs the time as a localtime variable, and it also wants to be able to format that time so that it can format the date and time as well. And it imports the saytime module and it calls that here.

It says "In Phoenix Arizona, it is now," and it has the saytime words. And it has the formatted date, on day of the week, and the day, month, and year. And so when we run that you'll see it has the CGI header because this is included in a page as a server side include. And it says, "In Phoenix, Arizona, it is now," and it gives the time, twenty-six til five, on this date. And so when you have code that you want to reuse you're going to want to put it in a module and when you put it in a module it's really just like writing a normal script.

You just need to be careful that you don't have any code that's outside of a class or a function, and you want to have this pattern down here at the bottom for running main. So that you have some way to test it or as I do with this one, to actually just use it as a script. Let's go ahead and take that out. It's still got the argument in there. So that when it's not run with the test argument it just runs it as a script and it gives the time so you can include it in a shell script or you can use it in a lot of different ways. So I'm looking for flexibility when I do this.

But that's essentially all there is to it. You just put your classes in there, set it up with the pattern at the bottom so that it only runs main when it's not imported, and so it doesn't do that when it's imported and then your class becomes available to other scripts. And you'll see a lot of examples of this as we go through the projects later on in the course.

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This video is part of

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Python 3 Essential Training

87 video lessons · 38764 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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