Frank Millman wrote:
> Hi all
>
> This is just out of curiosity.
>
> I have a tuple, and I want to create a new tuple with a new value in the
> first position, and everything else unchanged.
>
> I figured out that this would work -
>
>>>> t = ('a', 'b', 'c')
>>>> t2 = ('x',) + t[1:]
>>>> t2
> ('x', 'b', 'c')
>
> Then I thought I would neaten it a bit by replacing "('x',)" with "'x',"
> on the assumption that it is not necessary to surround a tuple with
> brackets.
>
> This is the result -
>
>>>> t = ('a', 'b', 'c')
>>>> t2 = 'x', + t[1:]
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> TypeError: bad operand type for unary +: 'tuple'
>>>>
>
> It is not a problem - I will just stick to using the brackets. However, I
> would be interested to find out the reason for the error.
>
> Version is 2.6.2.
>
> Thanks
the operator precedence. Sure you want to write
(a, -b, c)
to form a tuple with a negated (or actually all other kinds of expressions)
value in it. So python made -/+ and more or less all other operators
precede the comma, which is the actual tuple-operator. And consequently,
a, +(c, d)
tries to *first* apply + to the tuple (c, d) - which isn't defined.
Diez
--
http://mail.python.org/mailman/listinfo/python-list
