Suppose you are writing a Python program and want to check if a list is empty. How would you do it? This should be very straightforward, right? Or is it?
An example could be a list of fruits you are keeping track of. The list can be something like the following.
fruits = [ 'apple', 'orange', 'strawberry', 'peach', 'lemon' ]Suppose you want to check if the list of fruits is empty.
fruits = []You may be tempted to write code such as the following:
if len(fruits) == 0:
print('There are no fruits')Checking if the length of a list is zero is no longer preferred. It works but is not preferred. Many programmers have even called it unpythonic.
How about checking the list itself?
if fruits = []:
print('There are no fruits')It works, but this is also not preferred.
The preferred method is the following:
if not fruits:
print('There are no fruits')This is the pythonic way from the PEP 8 Style Guide.
Check Performance
There is a reason the preferred method is preferred. To check the performance, you can time how long each operation takes.
>>> import timeit
>>> min(timeit.repeat(lambda: len([]) == 0, repeat=200))
0.0980069637298584
>>> min(timeit.repeat(lambda: [] == [], repeat=200))
0.09142899513244629
>>> min(timeit.repeat(lambda: not [], repeat=200))
0.07426309585571289
>>> min(timeit.repeat(lambda: [], repeat=200))
0.06842684745788574As shown above, using the [] is the fastest. Checking with [] is slightly faster than not [], but they are faster than checking the length compared to 0 or checking against the empty list.
