Inconsistency in printing tuples in python

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 ?

To consider a single element as a tuple but not as just an element, you need a comma at the end. — shaik moeed
– shaik moeed, Commented Feb 25, 2020 at 6:45
Does this answer your question? What is the syntax rule for having trailing commas in tuple definitions? — Wouterr
– Wouterr, Commented Feb 25, 2020 at 6:50
yes that I understand but shouldn't the python interpreter should automatically trim the trailing comma and print ('hello'), since enclosing parenthesis are enough to determine that its a tuple, not a string otherwise — laxman
– laxman, Commented Feb 25, 2020 at 6:50
@Wouterr, the question is closely related but I am more concerned about reasoning as of why the printing of tuple is inconsistent. — laxman
– laxman, Commented Feb 25, 2020 at 6:57

Sayandip Dutta · Accepted Answer · 2020-02-25 11:21:03Z

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 ,.

Tony · Accepted Answer · 2020-02-25 06:47:20Z

because you define variable"singleton" as ("hello",), you don't need comma to end it, and for "foo", you define it, so it shows as what you defined

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