Facts

• In python, function is the first-class object. It's can be used as an argument.
• Function can be used as a return value.
  • return func1: reference to func1.
  • return func1(): results of evaluating func().
• Should we check the argument/input?: No! The responsibility is on the caller! Your function should be well-documented, that's it! (ref)

Create a normal function

If a function doesn't return any value, it returns None.

# without arguments
def func_name():
  pass

# with arguments
def func_name(<args>):
  pass

# return
def func_name(<args>):
  return <some_thing>

# call a function
func_name(<args>)

Unpacking a function

def sum_and_div(num1, num2):
  sum_nums = num1 + num2
  div_nums = num1 / num2
  return sum_nums, div_nums # multiple returns

sum, div = sum_and_div(18, 9)
print(sum, div)

# output
27 2.0

Functions with stars (args and *kwargs)

The *args will give you all function parameters as a tuple: (ref)

def foo(*args):
  print(args)
  for a in args:
    print(a)

foo(1)
foo(2, 3, 4)

# output
(1,)
1
(2, 3, 4)
2
3
4

def foo(rarg1, rarg2):
  print(rarg1, rarg2)

lst = [1, 2]
foo(*lst)
tpl = (3, 4)
foo(*tpl)

# output
1 2
3 4

If you wanna use "keywords arguments", use **args:

def kwfunc(**kwargs):
  print(type(kwargs))
  print(kwargs)

kwfunc()
kwfunc(kw1="thi", kw2="dinh")

# output
<class 'dict'>
{}
<class 'dict'>
{'kw1': 'thi', 'kw2': 'dinh'}

Use a dictionary as an input,

def kwfunc(**kwargs): # must have **
  print(kwargs)

kwargs = {'kw1': "thi", 'kw2': "dinh"}
kwfunc(**kwargs) # must have **

# output
{'kw1': 'thi', 'kw2': 'dinh'}

def kwfunc(kw1="john", kw2="doe"):
  print(kw1, kw2)

kwargs = {'kw1': "thi", 'kw2': "dinh"}

kwfunc()
kwfunc(kwargs) # goes to kw1
kwfunc(**kwargs) # goes to both kw1 & kw2

# output
john doe
{'kw1': 'thi', 'kw2': 'dinh'} doe
thi dinh

Coupling rargs, *args and **kwargs: