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Using named function arguments

From: Python 3 Essential Training

Video: Using named function arguments

Sometimes it's convenient to be able to pass named parameters into a function, and there is facility for that in Python. Go head and make a working copy of functions.py and we'll call it functions-working.py and open that working copy and here we have our little test function. Sometimes you might want to pass parameters to it and have them look like this. one=1, two=2, four=42, and so here you are actually passing named arguments and the caller is naming them rather than the receiver.

Using named function arguments

Sometimes it's convenient to be able to pass named parameters into a function, and there is facility for that in Python. Go head and make a working copy of functions.py and we'll call it functions-working.py and open that working copy and here we have our little test function. Sometimes you might want to pass parameters to it and have them look like this. one=1, two=2, four=42, and so here you are actually passing named arguments and the caller is naming them rather than the receiver.

So these arguments are not named on the receiving end. So these are specified with the two asterisks and very commonly called kwargs for keyword args, keyword arguments, and these are accessed like this. kwargs is actually a dictionary and so I can say kwargs sub 'one', like that, and kwargs sub 'two', kwargs sub 'four' and when I save these and run it, you see that we are getting those values here, 1, 2, and 42.

These keyword arguments can be combined with normal positional arguments, so you can pass it 5, 6, 7, 8, 9, and 10 and these can be named arguments. this, that and other and they can even be tuple arguments. And so what this will do is this will pass the named arguments, these first three will be this, that, and other, and then these here will be in this tuple and then you have your named arguments.

The only restriction is that they must actually be specified in this order. Your named arguments first, your arbitrary tuple arguments after that, and your keyword argument after that. Other than that, there is no restriction on the number or even the type of all these arguments. So go ahead and take a look at all of those. We have this, that, and other and we will go ahead and look at the tuple all at once like that and we will save this and run it.

You see we have them orders 5, 6, 7, there is our tuple, and there is our keyword arguments. Now, the keywords arguments, of course, are optional and the names of the keywords are not necessarily known by the receiver, just like with the tuple. Let's go head and get rid of all of this and we will look at the keyword arguments first. For k in kwargs: print k and kwargsk sub k.

So this will print one per line each of the keyword arguments. I save this and run it. 4, 2, 1 just like with any dictionary. So if I change these up here, 3 and I have 17 and in fact you see we still have them. Of course, because it is a dictionary, it's going to come out in no particular order. But more often than not, you are going to use these keyword arguments for settings and flags and things like that and you'll test for them in your function, and you are not going to really be counting on the order in which they are presented.

On the other hand, the tuple arguments will be presented in the order that they are passed because they are being passed as a tuple. So if I say, for n in args: print(n), and we'll save that and run it, then we get those actually in the order that they were passed. So that's how you can pass named arguments to a function. This is very commonly used for settings and flags and things like that and also, this is how you can combine them with the arbitrary tuple arguments and with your normal positional arguments.

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This video is part of

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Python 3 Essential Training

87 video lessons · 39366 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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