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Super Kai (Kazuya Ito)
Super Kai (Kazuya Ito)

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Unpacking in Python (5)

#python #iterable #unpack #asterisk

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*Memo:

  • My post explains the iterable unpacking with * and a function (2).
  • 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 dictionary unpacking with ** within a dictionary and function.
  • My post explains *args.
  • My post explains **kwargs.

Iterable unpacking can be done with * and print() as shown below:

*Memo:

  • One or more *iterables can be used as the arguments within a function call including print() to unpack them into the one or more parameters including *args but excluding **kwargs within a function definition and used within a list, tuple or set to unpack iterables:
    • One or more *iterables can be used with print() and *args but not with **kwargs.
  • The only one parameter with * which is *args conventionally can be used within a function definition:
    • A *args is the tuple parameter which can flexibly accept zero or more positional arguments so the type is tuple.
    • A *args is called a var-positional parameter.
    • A *args is the optional parameter with the immutable default value () so the default value () cannot be changed with =.
    • All the parameters after *args are keyword-only parameters so keyword arguments must be set to them.
    • *args can be other names like *teachers, *students, etc.
  • A * is called an iterable unpacking operator to unpack an iterable as the name suggests so the one or more *iterables used as the arguments within a function call including print() and used within a list, tuple or set to unpack iterables are iterable unpacking operators but the *args used within a function definition to flexibly accept zero or more positional arguments isn't an iterable unpacking operator:
    • The iterable unpacking operator * can unpack(flat) only the most outer dimension of an iterable.
  • A string(str) can be unpacked infinitely because even the single character unpacked is also the string(str) which is an iterable.

<Iterable unpacking within print()>: 

print(*[0, 1, *[2]], *[3, 4]) # list print(*(0, 1, *(2,)), *(3, 4)) # tuple print(*{0, 1, *{2}}, *{3, 4}) # set print(*frozenset({0, 1, *frozenset({2}), # frozenset  *frozenset({3, 4})})) print(*iter([0, 1, *iter([2]), *iter([3, 4])])) # iterator print(*'012', *'34') # str print(*range(3), *range(3, 5)) # range # 0 1 2 3 4  print(*{0:1, 2:3, 4:5}, *{6:7, 8:9}) # dict print(*{0:1, 2:3, 4:5}.keys(), *{6:7, 8:9}.keys()) # dict.keys() # 0 2 4 6 8  print(*{0:1, 2:3, 4:5}.values(), *{6:7, 8:9}.values()) # dict.values() # 1 3 5 7 9  print(*{0:1, 2:3, 4:5}.items(), *{6:7, 8:9}.items()) # dict.items() # (0, 1) (2, 3) (4, 5) (6, 7) (8, 9)  print(*b'012', *b'34') # bytes print(*bytearray(b'012'), *bytearray(b'34')) # bytearray # 48 49 50 51 52  # list # bytes # set print(*[0, 1, *[2, 3, *[4]]], *b'01234', *{0, 1, *{2, 3, *{4}}}) # 0 1 2 3 4 48 49 50 51 52 0 1 2 3 4
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<Iterable unpacking within a list>: 

print([*[0, 1, *[2]], *[3, 4]]) # list print([*(0, 1, *(2,)), *(3, 4)]) # tuple print([*{0, 1, *{2}}, *{3, 4}]) # set print([*frozenset({0, 1, *frozenset({2})}), # frozenset  *frozenset({3, 4})]) print([*iter([0, 1, *iter([2])]), *iter([3, 4])]) # iterator print([*range(3), *range(3, 5)]) # range # [0, 1, 2, 3, 4]  print([*{0:1, 2:3, 4:5}, *{6:7, 8:9}]) # dict print([*{0:1, 2:3, 4:5}.keys(), *{6:7, 8:9}.keys()]) # dict.keys() # [0, 2, 4, 6, 8]  print([*{0:1, 2:3, 4:5}.values(), *{6:7, 8:9}.values()]) # dict.values() # [1, 3, 5, 7, 9]  print([*{0:1, 2:3, 4:5}.items(), *{6:7, 8:9}.items()]) # dict.items() # [(0, 1), (2, 3), (4, 5), (6, 7), (8, 9)]  print([*'012', *'34']) # str # ['0', '1', '2', '3', '4']  print([*b'012', *b'34']) # bytes print([*bytearray(b'012'), *bytearray(b'34')]) # bytearray # [48, 49, 50, 51, 52]  # list # bytes # set print([*[0, 1, *[2, 3, *[4]]], *b'01234', *{0, 1, *{2, 3, *{4}}}]) # [0, 1, 2, 3, 4, 48, 49, 50, 51, 52, 0, 1, 2, 3, 4]
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<Iterable unpacking within a tuple>: 

print((*[0, 1, *[2]], *[3, 4])) # list print((*(0, 1, *(2,)), *(3, 4))) # tuple print((*{0, 1, *{2}}, *{3, 4})) # set print((*frozenset({0, 1, *frozenset({2})}), # frozenset  *frozenset({3, 4}))) print((*iter([0, 1, *iter([2])]), *iter([3, 4]))) # iterator print((*range(3), *range(3, 5))) # range # (0, 1, 2, 3, 4)  print((*{0:1, 2:3, 4:5}, *{6:7, 8:9})) # dict print((*{0:1, 2:3, 4:5}.keys(), *{6:7, 8:9}.keys())) # dict.keys() # (0, 2, 4, 6, 8)  print((*{0:1, 2:3, 4:5}.values(), *{6:7, 8:9}.values())) # dict.values() # (1, 3, 5, 7, 9)  print((*{0:1, 2:3, 4:5}.items(), *{6:7, 8:9}.items())) # dict.items() # ((0, 1), (2, 3), (4, 5), (6, 7), (8, 9))  print((*'012', *'34')) # str # ('0', '1', '2', '3', '4')  print((*b'012', *b'34')) # bytes print((*bytearray(b'012'), *bytearray(b'34'))) # bytearray # (48, 49, 50, 51, 52)  # list # bytes # set print((*[0, 1, *[2, 3, *[4]]], *b'01234', *{0, 1, *{2, 3, *{4}}})) # (0, 1, 2, 3, 4, 48, 49, 50, 51, 52, 0, 1, 2, 3, 4)
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<Iterable unpacking within a set>: 

print({*[0, 1, *[2]], *[3, 4]}) # list print({*(0, 1, *(2,)), *(3, 4)}) # tuple print({*{0, 1, *{2}}, *{3, 4}}) # set print({*frozenset({0, 1, *frozenset({2})}), # frozenset  *frozenset({3, 4})}) print({*iter([0, 1, *iter([2])]), *iter([3, 4])}) # iterator print({*range(3), *range(3, 5)}) # range # {0, 1, 2, 3, 4}  print({*{0:1, 2:3, 4:5}, *{6:7, 8:9}}) # dict print({*{0:1, 2:3, 4:5}.keys(), *{6:7, 8:9}.keys()}) # dict.keys() # {0, 2, 4, 6, 8}  print({*{0:1, 2:3, 4:5}.values(), *{6:7, 8:9}.values()}) # dict.values() # {1, 3, 5, 7, 9}  print({*{0:1, 2:3, 4:5}.items(), *{6:7, 8:9}.items()}) # dict.items() # {(0, 1), (2, 3), (6, 7), (4, 5), (8, 9)}  print({*'012', *'34'}) # str # {'3', '2', '1', '4', '0'}  print({*b'012', *b'34'}) # bytes print({*bytearray(b'012'), *bytearray(b'34')}) # bytearray # {48, 49, 50, 51, 52}  # list # bytes # set print({*[0, 1, *[2, 3, *[4]]], *b'01234', *{0, 1, *{2, 3, *{4}}}}) # {0, 1, 2, 3, 4, 48, 49, 50, 51, 52}
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<Iterable unpacking within a dictionary>: 

print({'A':'B', *[0, 1, 2]:'C', 'D':'E'}) # list print({'A':'B', *(0, 1, 2):'C', 'D':'E'}) # tuple print({'A':'B', *{0, 1, 2}:'C', 'D':'E'}) # set print({'A':'B', *frozenset({0, 1, 2}):'C', 'D':'E'}) # frozenset print({'A':'B', *{0:1, 2:3, 4:5}:'C', 'D':'E'}) # dict print({'A':'B', *{0:1, 2:3, 4:5}.keys():'C', 'D':'E'}) # dict.keys() print({'A':'B', *{0:1, 2:3, 4:5}.values():'C', 'D':'E'}) # dict.values() print({'A':'B', *{0:1, 2:3, 4:5}.items():'C', 'D':'E'}) # dict.items() print({'A':'B', *iter([0, 1, 2]):'C', 'D':'E'}) # iterator print({'A':'B', *'012':'C', 'D':'E'}) # str print({'A':'B', *b'012':'C', 'D':'E'}) # bytes print({'A':'B', *bytearray(b'012'):'C', 'D':'E'}) # bytearray print({'A':'B', *range(3):'C', 'D':'E'}) # range # SyntaxError: invalid syntax  print({'A':'B', 'C':*[0, 1, 2], 'D':'E'}) # list print({'A':'B', 'C':*(0, 1, 2), 'D':'E'}) # tuple print({'A':'B', 'C':*{0, 1, 2}, 'D':'E'}) # set print({'A':'B', 'C':*frozenset({0, 1, 2}), 'D':'E'}) # frozenset print({'A':'B', 'C':*{0:1, 2:3, 4:5}, 'D':'E'}) # dict print({'A':'B', 'C':*{0:1, 2:3, 4:5}.keys(), 'D':'E'}) # dict.keys() print({'A':'B', 'C':*{0:1, 2:3, 4:5}.values(), 4:5}) # dict.values() print({'A':'B', 'C':*{0:1, 2:3, 4:5}.items(), 4:5}) # dict.items() print({'A':'B', 'C':*iter([0, 1, 2]), 4:5}) # iterator print({'A':'B', 'C':*'012', 4:5}) # str print({'A':'B', 'C':*b'012', 4:5}) # bytes print({'A':'B', 'C':*bytearray(b'012'), 4:5}) # bytearray print({'A':'B', 'C':*range(3), 4:5}) # range # SyntaxError: cannot use a starred expression in a dictionary value
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