The Python documentation specifies that is is legal to omit the parentheses if a function only takes a single parameter, but
myfunction "Hello!"
generates a syntax error. So, what's the deal?
(I'm using Python 3.1)
EDIT:
The statement that I read only applies to generator expressions :
The parentheses can be omitted on calls with only one argument.
For your edit:
If you write down a generator expression, like stuff = (f(x) for x in items)
you need the brackets, just like you need the [ .. ]
around a list comprehension.
But when you pass something from a generator expression to a function (which is a pretty common pattern, because that's pretty much the big idea behind generators) then you don't need two sets of brackets - instead of something like s = sum((f(x) for x in items))
(outer brackets to indicate a function call, inner for the generator expression) you can just write sum(f(x) for x in items)
Without parentheses those wouldn't be functions
but statements
or keywords
(language-intrinsic).
This StackOverflow thread (with some very nice answers) contains a lead as to how one can create their own in pure Python (through advanced hackery, and not a good idea in 99.99% of the cases).
As I understand the rule is only about the generator expressions... so for example: sum(x 2 for x in range(10)), but you would still have to write: reduce(operator.add, (x 2 for x in range(10))).
This doesn't apply for generic functions though.
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