[Tutor] Python question 4.8.2. Keyword Argument

[dn]

On 6/03/24 06:52, Desiree C .Thomas wrote:
> Hello there,
> 
> I hope this reaches you well.
> 
> So I am following this https://docs.python.org/3/tutorial/controlflow.html
> 
> I'm on 4.8.2. Keyword Argument
> Following the example
> 
> def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):
>      print("-- This parrot wouldn't", action, end=' ')
>      print("if you put", voltage, "volts through it.")
>      print("-- Lovely plumage, the", type)
>      print("-- It's", state, "!")
> 
> So this is positional arguments
> 
> parrot(1000)                                          # 1 positional argument
> parrot(voltage=1000)                                  # 1 keyword argument
> parrot(voltage=1000000, action='VOOOOOM')             # 2 keyword arguments
> parrot(action='VOOOOOM', voltage=1000000)             # 2 keyword arguments
> parrot('a million', 'bereft of life', 'jump')         # 3 positional arguments
> parrot('a thousand', state='pushing up the daisies')
> 
> 
>    1.  So I understand the parrot(1000) would just input into the required argument voltage
>    2.  Parrot voltage=1000 also input into the required argument voltage
>    3.
> parrot(voltage=1000000, action='VOOOOOM') I can enter the requirement argument and skip one of the arguments to input into action. The other non stated arguments just use the default values.
>    4.
> parrot(action='VOOOOOM', voltage=1000000) Here I accepted that I can state on the arguments I want to filled in just as long as the requirement argument is inputted. I also accepted that the requirement argument doesn't need to be declare first either.
>    5.
> parrot('a million', 'bereft of life', 'jump') The requirement argument was filled and the remaining two arguments were inputted in the respective order of the functions
>    6.
> parrot('a thousand', state='pushing up the daisies') I have accepted that the requirement argument was assumed to the first argument and accept to be 'a thousand' and the declared argument was input
> 
> Please feel free of my understanding so far.
> So continuing
> 
> 
> parrot()
> 
> The requirement argument isn't inputted therefore error.
> 
> 
> parrot(voltage=5.0, 'dead')
> 
> This is the error I get: SyntaxError: positional argument follows keyword argument on line 10
> 
>  From my understanding, I thought the voltage should accept voltage to be 5.0 and update state into 'dead'? Can I get an explaination for this error.


You've spotted that there are different ways of looking at function's 
parameters:

- positional
- keyword, and
- default value

A positional-parameter must be matched with an argument at every 
function-call. The choice of description is that the position of each 
argument must match that of the function's parameter.

Contrarily keyword-parameters have no requirement for relative 
positioning, and as you've observed may be supplied in any order.

A default-parameter can be considered to be optional- if it is not 
supplied with an argument-value, then the default is substituted. It's 
behavior is otherwise that of a keyword-parameter.


Now for the slightly-confusing part:

- just because a parameter is "positional", doesn't stop us from 
labeling an argument as if it were a keyword-parameter.

- just because a parameter is "keyword", doesn't stop us from listing 
the arguments without labels and as if they are positional.

Oh great!

ie don't look for hard-and-fast rules, because Python is *flexible*!


Then the issue is what happens when there is a mix of positional- and 
keyword-arguments in the same function-call?

The rule is that we can start with positional-arguments, but once a 
keyword-argument has been used, every argument thereafter must be a 
keyword-argument.

So, positional-arguments first, and keyword-arguments last!

The positional-arguments must be in-order. The keyword-arguments may be 
in any sequence.


Question (which may have occurred to you):
what happens if we call

	parrot( 10_000, "dead", "voom", state="just resting" )

- which argument is applied to the state parameter?
(for you to consider and then dis/prove...)


To round-off (the difference between keyword-parameters and 
default-values): arguments are required for positional-parameters (as 
noted), whereas parameters with default-values may be omitted (optional).

Thus, (rare case) if use a keyword-parameter which does NOT have a 
default-value, an argument must be provided (whether in positional or 
keyword style).


(I've ignored the / and * symbols for defining parameter-types that follow)

-- 
Regards,
=dn