A test for special parameters in Python 3.12 + explanation for beginners

positional-keyword-arguments.py

def baz(
    a: int,
    b: int,
    /,
    c: int | None = None,
    *args: int,
    d: int | None = None,
    **kwargs: int,
) -> None:
    print("--------------------")
    print(f"a: {a}, b: {b}")
    print(f"c: {c}")
    print(f"args: {args}")
    print(f"d: {d}")
    print(f"kwargs: {kwargs}")


baz(1, 2)  # Minimal call with position-only arguments
baz(1, 2, 3, 4, 5)  # Adding more positional arguments
baz(1, 2, c=3, d=4, e=5)  # Using keyword arguments for c, d, and an extra one
baz(1, 2, 3, 4, d=5, e=6)  # Mixing positional and keyword arguments

stdout

--------------------
a: 1, b: 2
c: None
args: ()
d: None
kwargs: {}
--------------------
a: 1, b: 2
c: 3
args: (4, 5)
d: None
kwargs: {}
--------------------
a: 1, b: 2
c: 3
args: ()
d: 4
kwargs: {'e': 5}
--------------------
a: 1, b: 2
c: 3
args: (4,)
d: 5
kwargs: {'e': 6}

Analysis:

1. baz(1, 2)

   • Output:

     --------------------
     a: 1, b: 2
     c: None
     args: ()
     d: None
     kwargs: {}
     

   • Only the position-only arguments a and b are provided, with default values for the rest

2. baz(1, 2, 3, 4, 5)

   • Output:

     --------------------
     a: 1, b: 2
     c: 3
     args: (4, 5)
     d: None
     kwargs: {}
     

   • c is specified by position, and args captures the additional positional arguments 4 and 5.

3. baz(1, 2, c=3, d=4, e=5)

   • Output:

     --------------------
     a: 1, b: 2
     c: 3
     args: ()
     d: 4
     kwargs: {'e': 5}
     

   • c and d are specified by keyword, and e is stored in kwargs.

4. baz(1, 2, 3, 4, d=5, e=6)

   • Output:

     --------------------
     a: 1, b: 2
     c: 3
     args: (4,)
     d: 5
     kwargs: {'e': 6}
     

   • c is specified by position, args captures 4, and d and e are in d and kwargs, respectively