CODEWITHSUNDEEP
pythonpython-3.x
Dmytro Starosud
Dmytro Starosud

Reputation: 396

python unpack zero elements

please consider following code snippet:

# state that items contains two or more elements
x, y, *_ = items

# state that items contains exactly two elements
x, y, = items

# state that items contains exactly one element
x, = items

Can I state that items contains exactly zero elements in the similar way?

Thanks in advance!

Upvotes: 1

Views: 206

Answers (2)

Kasravnd
Kasravnd

Reputation: 107307

Not in a similar way but you can try to do access to the iterable's first item. If it raised an exception the iterable is empty. This method is famous as EAFP manner (Easier to ask for forgiveness than permission.). Or you can check if iterable is empty or not by checking the boolean value if the iterable. With that being said, for an iterator you can use next() method, for iterables you can use indexing (__getitem__), etc.

# Easier to ask for forgiveness than permission.
In [41]: try:
    ...:     item[0]
    ...: except:
    ...:     print("empty list")
empty list

# Or

In [45]: items = iter([])

In [46]: try:
    ...:     next(items)
    ...: except StopIteration:
    ...:     print("empty list")
    ...:     
empty list

Upvotes: 0

llllllllll
llllllllll

Reputation: 16414

You can use:

() = items

ValueError will raise if items has more than 0 elements.

This is valid in Python 3.6:

>>> items = []
>>> () = items
>>> items = [1,2]
>>> () = items
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: too many values to unpack (expected 0)

Upvotes: 1

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