In Python 3, the following returns a map object:
map(lambda x: x**2, range(10))
If we want to turn this object into a list, we can just cast it as a list using list(mapobject). However, I discovered through code golfing that
*x, = mapobject
makes x into a list. Why is this allowed in Python 3?
This is an example of extended iterable unpacking, introduced into Python 3 by PEP 3132:
This PEP proposes a change to iterable unpacking syntax, allowing to specify a "catch-all" name which will be assigned a list of all items not assigned to a "regular" name.
An example says more than a thousand words:
>>> a, *b, c = range(5) >>> a 0 >>> c 4 >>> b [1, 2, 3]
As usual in Python, singleton tuples are expressed using a trailing comma, so that the extended equivalent of this:
>>> x, = [1]
>>> x
1
… is this:
>>> *x, = range(3)
>>> x
[0, 1, 2]
*x, = iterablesyntax, I don't think someone else looking for an answer to Sandeep's question would find it as easily there as here. Thanks for not immediately hammering it, anyway ... I'll take this to chat and see what a larger group thinks.