*Memo:
-
My post explains the unpacking with a
for
statement (2). -
My post explains the unpacking with a
for
statement (3). - My post explains the unpacking with an assignment statement (1).
- My post explains the unpacking with an assignment 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 iterable unpacking with
*
and a function (3). -
My post explains the dictionary unpacking with
**
and a function. -
My post explains
*args
. -
My post explains
**kwargs
.
Iterable unpacking can be done without *
and with a for
statement as shown below:
*Memo:
- The syntax of the one or more variables and commas(
,
), tuples(()
) and/or lists([]
) within iterable
is an iterable unpacking:-
for v, in [[0]]:
andfor v in [[0]]:
are different. - One or more variables and commas are a tuple even if
()
isn't used. - Lists are converted to tuples if lists are explicitly used on the left side of
in
:
-
- The number of variables must match the number of the elements in each iterable in an iterable unless a
*variable
is used on the left side ofin
:- Only one
*variable
can be used within each tuple and list on the left side ofin
to flexibly accept the zero or more elements of an iterable:- A
*variable
is the list whose default value is[]
so the type islist
. - A
*variable
cannot be used outside any list and tuple.
- A
- A
**variable
cannot be used.
- Only one
- One or more
*iterables
can be used within each list, tuple and set literal within the most outer list, tuple and set literal on the right side ofin
to unpack iterables:- One or more
*iterables
exceptstr
anddict.items()
cannot be used outside any list, tuple and set literal within the most outer list, tuple and set literal. - A
*iterable
cannot be used outside any list, tuple and set literal. - A
*iterable
cannot be used within a dictionary(dict) literal.
- One or more
- 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:- One or more
*iterables
can be used withinprint()
and with*args
but not with**kwargs
.
- One or more
- One or more
**dictionaries
can be used within each dictionary literal within the most outer list, tuple and set literal on the right side ofin
to unpack dictionaries:- A
**dictionary
cannot be used outside any dictioanry(dict) literal. -
**
cannot be used with an iterable except a dictionary.
- A
- A
*
is called an iterable unpacking operator to unpack an iterable as the name suggests so the one or more*iterables
used within each list, tuple and set literal within the most outer list, tuple and set literal on the right side ofin
and used as the arguments within a function call includingprint()
to unpack iterables are iterable unpacking operators but the only one*variable
used within each tuple and list on the left side ofin
to flexibly accept the zero or more elements of an iterable isn't an iterable unpacking operator:- The iterable unpacking operator
*
can unpack(flat) only the most outer dimension of an iterable.
- The iterable unpacking operator
- A
**
is called a dictionary unpacking operator to unpack a dictionary as the name suggests so the one or more**dictionaries
used within each dictionary(dict) literal within the most outer list, tuple and set literal on the right side ofin
to unpack dictionaries are dictionary unpacking operators:- The dictionary unpacking operator
**
can unpack(flat) only the most outer dimension of a dictionary.
- The dictionary unpacking operator
- A string(
str
) can be unpacked infinitely because even the single character unpacked is also the string(str
) which is an iterable. -
The doc explains a
for
statement.
for v1, v2, v3 in [[0, 1, 2], [3, 4, 5]]: # list(list)
# for v1, v2, v3 in ((0, 1, 2), (3, 4, 5)): # tuple(tuple)
# for v1, v2, v3 in iter([iter([0, 1, 2]), # iterator(iterator)
# iter([3, 4, 5])]):
# for v1, v2, v3 in ['012', '345']: # list(str)
# for v1, v2, v3 in [range(3), range(3, 6)]: # list(range)
print(v1, v2, v3)
# 0 1 2
# 3 4 5
for v1, v2, v3 in {frozenset({0, 1, 2}), # set(frozenset)
frozenset({3, 4, 5})}:
# for v1, v2, v3 in frozenset({frozenset({0, 1, 2}), # frozenset(frozenset)
# frozenset({3, 4, 5})}):
print(v1, v2, v3)
# 3 4 5
# 0 1 2
for v1, v2, v3 in [{0:1, 2:3, 4:5}, # list(dict)
{6:7, 8:9, 10:11}]:
# for v1, v2, v3 in [{0:1, 2:3, 4:5}.keys(), # list(dict.keys())
# {6:7, 8:9, 10:11}.keys()]:
print(v1, v2, v3)
# 0 2 4
# 6 8 10
for v1, v2, v3 in [{0:1, 2:3, 4:5}.values(), # list(dict.values())
{6:7, 8:9, 10:11}.values()]:
print(v1, v2, v3)
# 1 3 5
# 7 9 11
for v1, v2, v3 in [{0:1, 2:3, 4:5}.items(), # list(dict.items())
{6:7, 8:9, 10:11}.items()]:
print(v1, v2, v3)
# (0, 1) (2, 3) (4, 5)
# (6, 7) (8, 9) (10, 11)
for v1, in '012345': # str
for v2, in v1:
for v3, in v2:
print(v1, v2, v3)
# 0 0 0
# 1 1 1
# 2 2 2
# 3 3 3
# 4 4 4
# 5 5 5
for v1, v2, v3 in [b'012', b'345']: # list(bytes)
# for v1, v2, v3 in [bytearray(b'012'), # list(bytearray)
# bytearray(b'345')]:
print(v1, v2, v3)
# 48 49 50
# 51 52 53
for v1, v2, v3 in [[0, 1, 2], [3, 4, 5]]:
# for (v1, v2, v3) in [[0, 1, 2], [3, 4, 5]]:
# for [v1, v2, v3] in [[0, 1, 2], [3, 4, 5]]:
print(v1, v2, v3)
# 0 1 2
# 3 4 5
for v1, v2 in [[0, [1, [2]]], [3, [4, [5]]]]:
# for (v1, v2) in [[0, [1, [2]]], [3, [4, [5]]]]:
# for [v1, v2] in [[0, [1, [2]]], [3, [4, [5]]]]:
print(v1, v2)
# 0 [1, [2]]
# 3 [4, [5]]
for v1, (v2, v3) in [[0, [1, [2]]], [3, [4, [5]]]]:
# for v1, [v2, v3] in [[0, [1, [2]]], [3, [4, [5]]]]:
# for (v1, (v2, v3)) in [[0, [1, [2]]], [3, [4, [5]]]]:
# for [v1, [v2, v3]] in [[0, [1, [2]]], [3, [4, [5]]]]:
print(v1, v2, v3)
# 0 1 [2]
# 3 4 [5]
for v, in [[0]]:
# for (v,) in [[0]]:
# for [v] in [[0]]:
print(v)
# 0
# It's not an iterable unpacking.
for v in [[0, 1, 2], [3, 4, 5]]:
print(v)
# [0, 1, 2]
# [3, 4, 5]
# It's not an iterable unpacking.
for v in [[0], [1]]:
print(v)
# [0]
# [1]
for v1, v2, v3 in [[0], [1]]:
pass
# ValueError: not enough values to unpack (expected 3, got 2)
for v1, v2, v3 in [[0, 1, 2, 3], [4, 5, 6, 7]]:
pass
# ValueError: too many values to unpack (expected 3)
for v, in [[], []]:
pass
# ValueError: not enough values to unpack (expected 1, got 0)
for v, in [0, 1]:
pass
# TypeError: cannot unpack non-iterable int object
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