Pythonic way to unpack an iterator inside of a list

Question

I\'m trying to figure out what is the pythonic way to unpack an iterator inside of a list.

For example:

my_iterator = zip([1, 2, 3, 4], [1, 2, 3, 4]         


        

Answer 1

While the unpacking operator * is not often used for unpacking a single iterable into a list (therefore [*it] is a bit less readable than list(it)), it is handy and more Pythonic in several other cases:

1. Unpacking an iterable into a single list / tuple / set, adding other values:

mixed_list = [a, *it, b]

This is more concise and efficient than

mixed_list = [a]
mixed_list.extend(it)
mixed_list.append(b)

2. Unpacking multiple iterables + values into a list / tuple / set

mixed_list = [*it1, *it2, a, b, ... ]

This is similar to the first case.

3. Unpacking an iterable into a list, excluding elements

first, *rest = it

This extracts the first element of it into first and unpacks the rest into a list. One can even do

_, *mid, last = it

This dumps the first element of it into a don't-care variable _, saves last element into last, and unpacks the rest into a list mid.

4. Nested unpacking of multiple levels of an iterable in one statement

it = (0, range(5), 3)
a1, (*a2,), a3 = it          # Unpack the second element of it into a list a2
e1, (first, *rest), e3 = it  # Separate the first element from the rest while unpacking it[1]

This can also be used in for statements:

from itertools import groupby

s = "Axyz123Bcba345D"
for k, (first, *rest) in groupby(s, key=str.isalpha):
    ...