在python中打印元组不一致

Question

I have just started to learn python and following the docs on tuples, I came across this snippet,

>>> empty = ()
>>> singleton = 'hello',    # <-- note trailing comma
>>> len(empty)
0
>>> len(singleton)
1
>>> singleton
('hello',)

Following this I ran following snippet,

>>> foo=1,2,3,
>>> len(foo)
3
>>> foo
(1, 2, 3)

Why does singleton prints with an trailing comma , where as foo seems to trim it ?

Answer 1

Beacause ("Hello") is not a tuple, it is same as "Hello" .

>>> ("Hello")
'Hello'

in order to distinguish tuple with single element from a simple expression in () a , is necessary. Whereas (1,2,3) is clearly a collection of items, and as they are enclosed by () it can easily be inferred as a tuple , hence no need for a trailing , .

Answer 2

因为你将变量“singleton”定义为 ("hello",)，你不需要逗号来结束它，而对于“foo”，你定义了它，所以它显示为你定义的