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--- python3_unpacking [2018/08/06 10:45]
jguerin Added extended iterable unpacking examples.
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-====== Unpacking Sequences ======
-Sequences can be explicitly/implicitly //unpacked// into discrete, ordered units of some type. Unpacking happens automatically using the '','' (comma). (The syntax is also used for [[python3_tuples|Tuple]] construction.)
-Unpacking works //only// in instances where the number of variables used //exactly// matches the number of items in the sequence.
-In the below examples parenthesis are not required, and are included for clarity.
-=====Implicit Unpacking: Member Assignment=====
-The most common application of unpacking is to (shallow) copy items into named variables.
-====Lists====
-Unpacking a [[python3_lists|List]].
-<code python>
->>> seq = [1, 2, 3]
->>> (a, b, c) = seq  # a=1, b=2, c=3
-</code>
-====Tuples====
-Unpacking a [[python3_tuples|Tuple]].
-<code python>
->>> tup = ('a', 'b')
->>> (x, y) = tup # x='a', y='b'
-</code>
-====Strings====
-Unpacking the characters of a [[python3_strings|String]].
-<code python>
->>> (fst, snd, thd) = "abc" # fst='a', snd='b', thd='c'
-</code>
-=====In-Place Swap/Mutual Replacement=====
-Swapping objects.
-<code python>
->>> x = 1
->>> y = 2
->>> (x, y) = (y, x) # x=2, y=1
-</code>
-=====Explicit Unpacking: The * (Star) Operator=====
-The unary ''*'' (star) operator is used to explicitly indicate unpacking, often outside the context of assignment. Use is common when elements of a sequence are intended to be used as the parameters to a function.
-E.g., (Assume that ''seq'' contains 3 elements) ''fun(seq[0], seq[1], seq[2])'' could be rephrased more tersely as ''fun(*seq)''.
-====Unpacking Arguments====
-Consider printing values in a [[python3_lists|List]].
-<code python>
->>> print([1, 2, 3]) # legal, but performs a cast str([1, 2, 3])
-[1, 2, 3]
-</code>
-In many instances we may wish to print a list's elements, but not formatted as a Python3 ''list''.
-<code python>
->>> print(*[1, 2, 3]) # as though we indexed each individually
-2 3
-</code>
-====Extended Iterable Unpacking====
-Extended Iterable Unpacking (([[https://www.python.org/dev/peps/pep-3132/|PEP 3132]] - Extended Iterable Unpacking)) extends unpacking to allow sequences on the left hand side of an assignment.
-Like regular unpacking for member assignment, extended iterable unpacking is ''only'' allowed in instances where the Python3 interpreter can infer the number and position of arguments.
-===Unpacking First and Rest===
-<code python>
->>> (fst, *rest) = list(range(1, 10)) # fst=0, rest=[1, 2, ..., 9]
-</code>
-===Unpacking First, Rest, and Last===
-One or more additional named variables can be specified //before// or //after// the ''rest''.
-<code python>
->>> (first, *rest, last) = list(range(1, 10)) # first=0, rest=[2, 3, ..., 8], last=9
-</code>

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