Backticks: What up?

[Steven Brent]

I was wondering why the backticks in the following fragment:

return 'Here's the result: ' + `self.data`

My guess is that in a return statement (as opposed to a print statement)
it's necessary to do this in order to get the self.data instance attribute
as a string, so it can be concatenated with the 'Here's the result: '
string.

What exactly do the backticks do, then? Just return the result of an
expression as a string? Does my guess make sense and / or is it correct?
Elucidations and gentle ridicule welcome.

TIA.

[donald.welch@hp.com]

Re: Backticks: What up?

Steven Brent wrote:
[color=blue]
> I was wondering why the backticks in the following fragment:
>
> return 'Here's the result: ' + `self.data`
>
> My guess is that in a return statement (as opposed to a print statement)
> it's necessary to do this in order to get the self.data instance attribute
> as a string, so it can be concatenated with the 'Here's the result: '
> string.
>
> What exactly do the backticks do, then? Just return the result of an
> expression as a string? Does my guess make sense and / or is it correct?
> Elucidations and gentle ridicule welcome.
>
> TIA.[/color]

I think `self.data` is equivalent to repr(self.data) .

-Don

[David Goodger]

Re: Backticks: What up?

Backticks are equivalent to repr(). For any x:

`x` == repr(x)

Nothing to do with the return statement.

-- David Goodger

[Peter Hansen]

Re: Backticks: What up?

Steven Brent wrote:
[color=blue]
> I was wondering why the backticks in the following fragment:
>
> return 'Here's the result: ' + `self.data`
>
> My guess is that in a return statement (as opposed to a print statement)
> it's necessary to do this in order to get the self.data instance attribute
> as a string, so it can be concatenated with the 'Here's the result: '
> string.
>
> What exactly do the backticks do, then? Just return the result of an
> expression as a string? Does my guess make sense and / or is it correct?
> Elucidations and gentle ridicule welcome.[/color]

The above is equivalent to

return "Here's the result: %r" % self.data

Note that someone doing the `self.data` thing might really
have wanted to do the string representation instead (though
the two are often the same), so

return "Here's the result: %s" % self.data

would be more appropriate.

-Peter

[Peter Hansen]

Re: Backticks: What up?

Steven Brent wrote:
[color=blue]
> I was wondering why the backticks in the following fragment:
>
> return 'Here's the result: ' + `self.data`
>
> My guess is that in a return statement (as opposed to a print statement)
> it's necessary to do this in order to get the self.data instance attribute
> as a string, so it can be concatenated with the 'Here's the result: '
> string.
>
> What exactly do the backticks do, then? Just return the result of an
> expression as a string? Does my guess make sense and / or is it correct?
> Elucidations and gentle ridicule welcome.[/color]

I was looking for the proper language ref but sometimes they
can be hard to track down:

http://docs.python.org/ref/string-conversions.html

-Peter

[Steven Brent]

Re: Backticks: What up?

Thanks! I didn't know you could use printf type syntax with return....

[Steve Holden]

Re: Backticks: What up?

Steven Brent wrote:[color=blue]
> Thanks! I didn't know you could use printf type syntax with return....[/color]

The "return" statement allows an arbitratu expression as its target,
even complex objects like sequences, classes and instances. For example:
[color=blue][color=green][color=darkred]
>>> def tuplify(a, b):[/color][/color][/color]
.... return a, b
....[color=blue][color=green][color=darkred]
>>> tuplify([1, 2], [3, 4])[/color][/color][/color]
([1, 2], [3, 4])[color=blue][color=green][color=darkred]
>>> thing, thong = tuplify("sing", (1, 2, 3))
>>> thing[/color][/color][/color]
'sing'[color=blue][color=green][color=darkred]
>>> thong[/color][/color][/color]
(1, 2, 3)[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

regards
Steve