Eric. On 8/2/2015 11:57 AM, MRAB wrote:
On 2015-08-02 16:37, Eric V. Smith wrote:
On 8/1/2015 1:43 PM, Eric V. Smith wrote:
On 7/25/2015 3:55 PM, Eric V. Smith wrote:
In trying to understand the issues for a PEP, I'm working on a sample implementation. There, I've just disallowed concatentation entirely. Compared to all of the other issues, it's really insignificant. I'll put it back at some point.
I'm basically done with my implementation of f-strings.
Here's another issue. I can't imagine this will happen often, but it should be addressed. It has to do with literal expressions that begin with a left brace.
For example, this expression:
{x: y for x, y in [(1, 2), (3, 4)]} {1: 2, 3: 4}
If you want to put it in an f-string, you'd naively write:
f'expr={{x: y for x, y in [(1, 2), (3, 4)]}}' 'expr={x: y for x, y in [(1, 2), (3, 4)]}'
But as you see, this won't work because the doubled '{' and '}' chars are just interpreted as escaped braces, and the result is an uninterpreted string literal, with the doubled braces replaced by undoubled ones.
There's currently no way around this. You could try putting a space between the left braces, but that fails with IndentationError:
f'expr={ {x: y for x, y in [(1, 2), (3, 4)]}}' File "<fstring>", line 1 {x: y for x, y in [(1, 2), (3, 4)]} ^ IndentationError: unexpected indent
Why is there an IndentationError? It's an expression, not a statement, so leading spaces should be ignored.
Good question. I'm parsing it with PyParser_ASTFromString. Maybe I'm missing a compiler flag there which will ignore leading spaces. But in any event, the result is the same: You'll need to add a space here in order to disambiguate it from doubled braces. That's really the crux of the issue. Eric.