Posted on Sep 7

**kwargs in Python

#python #kwargs #keywordarguments #function

Buy Me a Coffee☕

*Memo:

My post explains the unpacking with an assignment statement (1).
My post explains the unpacking with an assignment statement (2).
My post explains the unpacking with a for statement (1).
My post explains the unpacking with a for statement (2).
My post explains the iterable unpacking with * and a function (1).
My post explains the iterable unpacking with * and a function (2).
My post explains the dictionary unpacking with ** within a dictionary and function.
My post explains *args.

**kwargs can be used in a function as shown below:

*Memo:

A **kwargs is the dictionary parameter which can flexibly accept zero or more keyward arguments so the type is dict.
A **kwargs is called a var-keyword parameter.
A **kwargs is the optional parameter with the immutable default value {} so the default value {} cannot be changed with =.
Only one **kwargs can be used in a function definition.
A **kwargs must be the last parameter.
A **kwargs can be other names like **teachers, **students, etc.
One or more **dictionaries can be used within a dictionary and as the arguments within a function call excluding print() to unpack them into the one or more parameters including **kwargs but excluding *args within a function definition and used within a dictionary to unpack dictionaries:
- One or more **dictionaries can be used with **kwargs but not with print() and *args.

def func(**kwargs): pass def func(A, **kwargs): pass def func(A='B', **kwargs): pass # No error  def func(**kwargs, **kwargs): pass # SyntaxError: * argument may appear only once  def func(**kwargs, A): pass def func(**kwargs, A='B'): pass # SyntaxError: arguments cannot follow var-keyword argument  def func(**kwargs='ABC'): pass # SyntaxError: var-keyword argument cannot have default value

<func(kwargs) with keyword arguments**>:

def func(**kwargs): print(kwargs) print({0:1, **kwargs, 2:3}) func() # {} # {0: 1, 2: 3}  func(A='B', C='D') func(**{'A':'B', 'C':'D'}) func(**{'A':'B'}, **{'C':'D'}) func(A='B', **{'C':'D'}) func(**{'A':'B'}, C='D') # {'A': 'B', 'C': 'D'} # {0: 1, 'A': 'B', 'C': 'D', 2: 3}

<func(A, kwargs) with keyword arguments**>:

def func(A='b', **kwargs): print(A, kwargs) print(A, {0:1, **kwargs, 2:3}) func() # b {} # b {0: 1, 2: 3}  func(A='B', C='D') func(**{'A':'B', 'C':'D'}) func(**{'A':'B'}, **{'C':'D'}) func(A='B', **{'C':'D'}) func(**{'A':'B'}, C='D') # B {'C': 'D'} # B {0: 1, 'C': 'D', 2: 3}

<func(kwargs) with positional arguments**>:

def func(**kwargs): print(kwargs) print(**kwargs) func() # {} # Nothing  func(0, 1, 2, 3, 4, 5) func(*[0, 1, 2, 3], *[4, 5]) # list func(*(0, 1, 2, 3), *(4, 5)) # tuple func(*{0, 1, 2, 3}, *{4, 5}) # set func(*frozenset({0, 1, 2, 3}), *frozenset({4, 5})) # frozenset func(0, 2, 4, 6, 8, 10) func(*{0:1, 2:3, 4:5, 6:7}, *{8:9, 10:11}) # dict func(*{0:1, 2:3, 4:5, 6:7}.keys(), # dict.keys()  *{8:9, 10:11}.keys()) func(*iter([0, 1, 2, 3]), *iter([4, 5])) # iterator func(*range(4), *range(4, 6)) # range func(1, 3, 5, 7, 9, 11) func(*{0:1, 2:3, 4:5, 6:7}.values(), # dict.values()  *{8:9, 10:11}.values()) func((0, 1), (2, 3), (4, 5), (6, 7), (8, 9), (10, 11)) func(*{0:1, 2:3, 4:5, 6:7}.items(), # dict.items()  *{8:9, 10:11}.items()) func('0', '1', '2', '3', '4', '5') func(*'0123', *'45') # str func(48, 49, 50, 51, 52, 53) func(*b'0123', *b'45') # bytes func(*bytearray(b'0123'), *bytearray(b'45')) # bytearray func(0, 1, 50, 3, 4, 5) func(*[0, 1], *b'2', *{3, 4, 5}) # TypeError: func() takes 0 positional arguments but 6 were given