bad operand type for unary +: tuple

[Frank Millman]

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):

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

Frank Millman

 

[Diez B. Roggisch]

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):

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

 

[Frank Millman]

t = ('a', 'b', 'c')
t2 = 'x', + t[1:]

Traceback (most recent call last):

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.

Makes total sense. Thanks, Diez

Frank