CODEWITHSUNDEEP
pythonpython-3.x
guo
guo

Reputation: 10219

Difference between max([a for a in [1,2]]) and max(a for a in [1,2]) in Python 3

I found both of them will output the expected result 2.

A generator is in form of (a for a in [1,2]). I doubt that the (a for a in [1,2]) insides max(a for a in [1,2]) is a generator. However, if that's the case, why can a pair of () be ignored? Technically speaking it should be max((a for a in [1,2])).

Thanks.

Upvotes: 3

Views: 68

Answers (1)

Carcigenicate
Carcigenicate

Reputation: 45806

That is in fact a generator expression. Generator expressions can make use of the () from argument lists; providing that they're the only argument passed to the function. If there are more arguments, they require their own pair of parenthesis.

You can verify this yourself with a quick test:

def func(arg):
    print(type(arg))

func(n for n in range(10))  # Prints <class 'generator'>

From PEP 289:

The syntax requires that a generator expression always needs to be directly inside a set of parentheses and cannot have a comma on either side. . . . [I]f a function call has a single positional argument, it can be a generator expression without extra parentheses, but in all other cases you have to parenthesize it.

Upvotes: 6

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