Getting only element from a single-element list in Python?

Question

When a Python list is known to always contain a single item, is there a way to access it other than:

mylist[0] 

You may ask, 'Why would you want to?'. Curiosity alone. There seems to be an alternative way to do everything in Python.

Answer 1

Raises exception if not exactly one item:

Sequence unpacking:

singleitem, = mylist # Identical in behavior (byte code produced is the same), # but arguably more readable since a lone trailing comma could be missed: [singleitem] = mylist 

All others silently ignore spec violation, producing first or last item:

Explicit use of iterator protocol:

singleitem = next(iter(mylist)) 

Destructive pop:

singleitem = mylist.pop() 

Negative index:

singleitem = mylist[-1] 

Set via single iteration for (because the loop variable remains available with its last value when a loop terminates):

for singleitem in mylist: break 

Rampant insanity:

# But also the only way to retrieve a single item and raise an exception on failure # for too many, not just too few, elements as an expression, rather than a statement, # without resorting to defining/importing functions elsewhere to do the work singleitem = (lambda x: x)(*mylist) 

There are many others (combining or varying bits of the above, or otherwise relying on implicit iteration), but you get the idea.

Answer 2

I will add that the more_itertools library has a tool that returns one item from an iterable.

from more_itertools import one   iterable = ["foo"] one(iterable) # "foo" 

In addition, more_itertools.one raises an error if the iterable is empty or has more than one item.

iterable = [] one(iterable) # ValueError: not enough values to unpack (expected 1, got 0)  iterable = ["foo", "bar"] one(iterable) # ValueError: too many values to unpack (expected 1) 

more_itertools is a third-party package > pip install more-itertools