How do I check if a list is empty?

2018-05-29 02:40:50

For example, if passed the following:

a = []

How do I check to see if a is empty?

if not a:
  print("List is empty")

使用空列表的隐式布尔型是相当pythonic。

The pythonic way to do it is from the PEP 8 style guide (where Yes means “recommended” and No means “not recommended”):

For sequences, (strings, lists, tuples), use the fact that empty sequences are false.

Yes: if not seq:
     if seq:

No:  if len(seq):
     if not len(seq):

I prefer it explicitly:

if len(li) == 0:
    print('the list is empty')

This way it's 100% clear that li is a sequence (list) and we want to test its size. My problem with if not li: ... is that it gives the false impression that li is a boolean variable.

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