How to check if a deque is empty in Python?
d is your deque, use
if d: # not empty else: # empty
This will implicitly convert
d to a
bool, which yields
True if the deque contains any items and
False if it is empty.
There are two main ways:
1) Containers can be used as booleans (with false indicating the container is empty):
2) Containers in Python also have a __len__ method to indicate their size.
Here are a few patterns:
non_empty = bool(d) # Coerce to a boolean value empty = not d # Invert the boolean value if d: # Test the boolean value print('non-empty') while d: # Loop until empty x = d.pop() process(x) if len(d) == 0: # Test the size directly print('empty')
The latter technique isn’t as fast or succinct as the others, but it does have the virtue of being explicit for readers who may not know about the boolean value of containers.
Other ways are possible. For example, indexing with
d raises an IndexError for an empty sequence. I’ve seen this used a few times.
Hope this helps 🙂