Python - 迭代list.append的结果

Question

为什么我不能这样做：

files = [file for file in ['default.txt'].append(sys.argv[1:]) if os.path.exists(file)]

Answer 1

list.append doesn't return anything in Python:

>>> l = [1, 2, 3]
>>> k = l.append(5)
>>> k
>>> k is None
True

You may want this instead:

>>> k = [1, 2, 3] + [5]
>>> k
[1, 2, 3, 5]
>>> 

Or, in your code:

files = [file for file in ['default.txt'] + sys.argv[1:] if os.path.exists(file)]

Answer 2

You could also use itertools.chain if you don't want to duplicate lists.

files = [file for file in itertools.chain(['default.txt'], sys.argv[1:])
                  if os.path.exists(file)]