[Python-ideas] Allowing comments after line continuations

[Terry Jan Reedy]

On 5/16/2013 2:41 PM, Bruce Leban wrote:

> The \ line continuation does not allow comments yet statements that span
> multiple lines may need internal comments.

In a string, \ escapes the immediate next character. This idea of \ at 
the *end* of a line, just before the newline character, is that it 
escapes the newline, *just as is does within a string*.

 >>> 'abd\
ed'
'abded'
 >>> 1 +\
   2
3

In both cases, one would typically have a syntax error without the \.

 >>> 'abc
SyntaxError: EOL while scanning string literal
 >>> a +
SyntaxError: invalid syntax

I think changing the correspondance is a bad idea. A code line is an 
string (but not an str object) that is fed to the interpreter.

Besides which, end of line \ is generally discouraged and nearly always 
not needed as openers other that ' and ", namely {,  [, and (, enable 
line continuation without \. So if you want comments on each line, add 
parens.

>     with a as x, \   # comment here may be useful
>           b as y, \   # or here
>           c as z: \   # or here
>          pass

This is one of the very few cases where bracketing is not allowed. I do 
not remember why. The PEP might say why not. See ho

 >>> from itertools import (chain, # very helpful
		     count)  # also helpful

Here () is allowed precisely for line continuation.

>     x = y +     # syntax error
>          z

x = (1 +  # not a syntax error
     2)    # and more comment

> Two reasons for requiring a space after the backslash:
>
> (1) make the backslash more likely to stand out visually (and we can't
> require a space before it)

I think it stands out better by itself at the end.


Terry Jan Reedy