How to unpack tuple of length n to m<n variables
In Python 3 I can do the following (see also PEP3132 on Extended Iterable Unpacking):
a, *b = (1, 2, 3)
# a = 1; b = (2, 3)
What can I do to achieve the same similarly elegant in Python 2.x?
I know that I could use single element access and slicing operations, but I wonder if there is a more pythonic way. My code so far:
a, b = (1, 2, 3)[0], (1, 2, 3)[1:]
# a = 1; b = (2, 3)
Answer
I found out that the related PEP3132 gives some examples for Python 2.x as well:
Many algorithms require splitting a sequence in a "first, rest" pair:
first, rest = seq[0], seq[1:][...]
Also, if the right-hand value is not a list, but an iterable, it has to be converted to a list before being able to do slicing; to avoid creating this temporary list, one has to resort to
it = iter(seq) first = it.next() rest = list(it)
Other approaches given in the answers to this question:
Function Argument List Unpacking Approach
requires an extra function definition/call:
def unpack(first, *rest):
return first, rest
first, rest = unpack( *seq )
I wonder why it is implemented in unpacking function argument lists but not for normal tuple unpacking.
Generator Approach
Credits. Also requires a custom function implementation. Is a little more flexible concerning the number of first variables.
def unpack_nfirst(seq, nfirst):
it = iter(seq)
for x in xrange(nfirst):
yield next(it, None)
yield tuple(it)
first, rest = unpack_nfirst(seq, 1)
The most pythonic would probably be the ones mentioned in the PEP above, I guess?