Links: PYTHON - PROGRAMMING
Rel: python decorators
Tags: #public

---

functions

***args **
- when unsure how many (additional) arguments might be passed into your function

def add_exclaim(*args)->list:
    fin = []
    for a in args:
        if not type(a) == str:
            a = str(a)
        a += '!'
        fin.append(a)   
    return fin


>>> 
>>> my_strs = ['this', 'is', 'rocket', 'science', 2]
>>> add_exclaim(*my_strs)
['this!', 'is!', 'rocket!', 'science!', '2!']

• when ensuring everything passes through your super() or @exampdec,
• can un-pack lists (iterables) into function calls with *

>>> def examp(x,y): pass
>>> li = ['this', 'that']
>>> examp(*li)
>>> # equivelant to:  {: id="equivelant-to:" }
>>> examp('this', 'that')
>>> # which would otherwise fail without unpacking, because it's a single list {: id="which-would-otherwise-fail-without-unpacking,-because-it's-a-single-list" }
>>> examp(['this', 'that'])
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: examp() missing 1 required positional argument: 'y'

>>> 
>>> # or get something weird you didn't want... {: id="or-get-something-weird-you-didn't-want..." }
>>> # with unpacking into a *args definition (above) {: id="with-unpacking-into-a-*args-definition-(above)" }
>>> add_exclaim(*my_strs)
['this!', 'is!', 'rocket!', 'science!', '2!']
>>> # ... without unpacking you get: {: id="...-without-unpacking-you-get:" }
>>> add_exclaim(my_strs)
>>> ["['this', 'is', 'rocket', 'science', 2]!"]
>>> # oops... {: id="oops..." }
>>> # -->  {: id="-->" }
>>> def add_exclaim(*args)->list:
    fin = []
    if len(args)  1 and type(args[0])  list:
        args = args[0]
    for a in args:
        if not type(a) == str:
            a = str(a)
        a += '!'
        fin.append(a)   
    return fin
>>> 
>>> x = ['this!', 'is!', 'rocket!', 'science!', '2!']
>>> add_exclaim(x)
['this!!', 'is!!', 'rocket!!', 'science!!', '2!!']
>>> add_exclaim(*x)
['this!!', 'is!!', 'rocket!!', 'science!!', '2!!']
>>> # ^^ very nice! {: id="^^-very-nice!" }

->

---

*kwargs
- key-word arguments; will fail if not named explicitly when calling the function/method
- any argument pre-defined (e.g. def func(y=None): pass) is a kwarg. This means, you have to call func() with y as func(y="this") aka now fail on func("this"), which as a positional argument by default in def func(y): pass would accept func("this") as y regardless. P.s. func() works just fine as y is happy with None.
- anything after * in a function definition is now a kwarg (even if it's not pre-defined), def examp(*, x, y=None): pass requires x and y to make a correct call examp(x='this', y='that'), where examp('this', y='that') fails, and again examp(x='this') works fine as y is still None unless otherwise stated when called.
- you cannot define a positional argument after a pre-defined kwarg e.g. def func(y=None, z): pass is a SyntaxError...
- you can unpack dict(-likes) with ** to provide kwargs (nice!):

>>> def examp(*, x, y=None): pass
>>> mydic = {'x': 'this', 'y': 'that'}
>>> examp(**mydic)
>>> # is equivelant to:  {: id="is-equivelant-to:" }
>>> examp(x='this', y='that'))
>>> # note: x and y are kwargs only! {: id="note:-x-and-y-are-kwargs-only!" }
>>> examp('this', 'that')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: examp() takes 0 positional arguments but 2 were given
>>> 

---

https://betterprogramming.pub/how-to-define-function-parameters-as-positional-keyword-or-both-in-python-8753ca2ac5ca

def blah(x,/,y,*,z):
    pass