I am having a problem understanding why one of the following line returns generator and another tuple.
How exactly and why a generator is created in the second line, while in the third one a tuple is produced?
sample_list = [1, 2, 3, 4]
generator = (i for i in sample_list)
tuple_ = (1, 2, 3, 4)
print type(generator)
<type 'generator'>
print type(tuple_)
<type 'tuple'>
Is it because tuple is immutable object and when I try to unpack list inside (), it can't create the tuple as it has to change the tuple tuple.
You can imagine tuples as being created when you hardcode the values, while generators are created where you provide a way to create the objects.
This works since there is no way (1,2,3,4) could be a generator. There is nothing to generate there, you just specified all the elements, not a rule to obtain them.
In order for your generator to be a tuple, the expression (i for i in sample_list) would have to be a tuple comprehension. There is no way to have tuple comprehensions, since comprehensions require a mutable data type.
Thus, the syntax for what should have been a tuple comprehension has been reused for generators.
Parentheses are used for three different things: grouping, tuple literals, and function calls. Compare (1 + 2) (an integer) and (1, 2) (a tuple). In the generator assignment, the parentheses are for grouping; in the tuple assignment, the parentheses are a tuple literal. Parentheses represent a tuple literal when they contain a comma and are not used for a function call.
来源：https://stackoverflow.com/questions/45849120/python-tuple-vs-generator