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Using standard library modules

From: Python 3 Essential Training

Video: Using standard library modules

The Python standard library has a number of modules that you can import into your programs and use for your own purposes. This page has a list of them starting here in section 7, under String Services. And you'll see that there are quite a few of them. So we're going to just go through a few of these, a few of the more common ones and show you as an example how you can use them. And I suggest that you go through this list at least once and just look out what they are. And just look at their descriptions.

Using standard library modules

The Python standard library has a number of modules that you can import into your programs and use for your own purposes. This page has a list of them starting here in section 7, under String Services. And you'll see that there are quite a few of them. So we're going to just go through a few of these, a few of the more common ones and show you as an example how you can use them. And I suggest that you go through this list at least once and just look out what they are. And just look at their descriptions.

Just read through the list, so you have an idea of the kinds of things that are available to you. So here in Eclipse, we're going to make a working copy of modules.py. Call this modules-working.py, and we'll open that up. You'll notice that here we're importing sys, and here on the web page you'll see sys is for system-specific parameters and functions. If we open that page, you'll see that there's full documentation on all of the things that you can do with sys.

So, one of these is to get the Python version. This is with sys version info. And so if we run this, you'll see that we say, this is Python version 3.1.2. You can also get the system platform. You can say print(sys.platform) and if we save that and run it, you'll see that this is win32. On my Mac at home it says Darwin and whatever operating system you're running Python on, it will give you an idea.

And this is a category of operating system. It's not actually the operating system. You can get the operating system from the OS module, but this gives you an indicator of what types of services are going to be available on this platform. Like, for instance, if I'm on a win32 platform, I'm not going to do things that are UNIX specific and vise-versa. So, that can be a useful token to see. If we import OS, this is another module that you'll find in that list, you'll notice that I can import inside of the function.

I don't need to do my import at the top. This allows me to actually selectively import things, say I read that sys.platform variable and say I'm going to do certain things one way or certain things another way depending on which platform I get. So I can import modules selectively, and the system won't try to import them if they're not on the right platform or whatever. So, here we can get the os.name for example, and if I save that and run it, you'll see this says nt.

So, that's the name that it's giving this particular type of Windows. And it distinguishes it like from, for example the older Windows 3 or something like that. I can get variables from the environment. I can print os.getenv and say I want the PATH variable. Save and run. And there is the PATH variable from the operating system. So, I can get current working directory, and we'll save and run that.

And there is the current working directory. Of course, this module has a lot of functions in it. Just one more I want to show is the urandom function. This is sometimes useful. Save and run that. This is a function that'll give a string of random bytes. And of course you see that this is the byte type, and I set 25 so it's 25 bytes long. Another useful module is the urllib module, and we'll go ahead and import from that urllib.request, and we'll grab a web page from the internet.

urllib.request.urlopen, and we'll give it a URL here. We'll go ahead and get my homepage, print(page). There we go. Save that and run it. We get this object. And that's an iterable object. So, we can iterate on it and say for line in page: print, and convert each line to a string because they come out binary, and we provide an encoding.

And they have no lines at the end of them. So we'll give it this line ending there. And we save and run and there is an entire web page. So, that's a really useful one. There are a lot of very useful modules in here. I'm just going to take a quick look at a couple of more. One is the random module. It's a very rich random number library. For example, you can print a random number from in a range. randint, A range between 1 and 1000. Save and run.

And then we have the number 726. If we run it again, we get a different number and a different number and a different number. And that's very useful. Another very useful method in this library is the shuffle method. It takes a list. I'm going to just give it a list with a range in it, and if we print that list, you'll see that we have a range of 25 numbers. We can shuffle the list, random.shuffle, and print it again.

And there we have the list shuffled randomly. If we do that a few times, save and run, you can see we get different shuffles each time. Finally, in our little partial tour of the standard library, look at the datetime module. So we'll save that and run it, and there we have the time as of right now when I'm recording this.

In fact, we can do this. now.year, now.month, now.day, now.hour, now.minute, now.second and now.microsecond, and save that and run it. And there we have all of those components, separately usable with these properties of the datetime object.

So, these are just a few of the standard modules that are available with Python. Again I strongly recommend that you look through the documentation for these standard modules. At least read their descriptions so that you get an idea of what's available there, so that as you're going through writing your own code, you're not tempted to reinvent the wheel. The modules that are included with Python and the Python distribution tend to be very well written. They tend to be very feature rich and they tend to be quite well optimized and reliable. So, I suggest that you use them when you have an opportunity.

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This video is part of

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Python 3 Essential Training

87 video lessons · 42134 viewers

Bill Weinman
Author

 
Expand all | Collapse all
  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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