Home Original page

[Python-Dev] Python Language Reference has no mention of list comÃprehensions

R. David Murray rdmurray at bitdance.com
Fri Dec 4 09:52:55 EST 2015 
On Fri, 04 Dec 2015 18:38:03 +1000, Nick Coghlan <ncoghlan at gmail.com> wrote:
> Summarising that idea:
> 
> * literals: any of the dedicated expressions that produce an instance
> of a builtin type
> * constant literal: literals that produce a constant object that can
> be cached in the bytecode
> * dynamic literal: literals containing dynamic subexpressions that
> can't be pre-calculated
> * display: legacy term for a dynamic literal (originally inherited from ABC)
> * comprehension: a dynamic literal that creates a new container from
> an existing iterable
> * lexical literal: constant literals and dynamic string literals [1]
> 
> The ast.literal_eval() docs would need a slight adjustment to refer to
> "literals (excluding container comprehensions and generator
> expressions)", rather than the current "literals and container
> displays".

Except that that isn't accurate either:

    >>> import ast
    >>> ast.literal_eval('[1, id(1)]')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/home/rdmurray/python/p36/Lib/ast.py", line 84, in literal_eval
        return _convert(node_or_string)
      File "/home/rdmurray/python/p36/Lib/ast.py", line 57, in _convert
        return list(map(_convert, node.elts))
      File "/home/rdmurray/python/p36/Lib/ast.py", line 83, in _convert
        raise ValueError('malformed node or string: ' + repr(node))
    ValueError: malformed node or string: <_ast.Call object at 0xb73633ec>

So it's really container displays consisting of literals, which we could
call a "literal container display".

I think the intuitive notion of "literal" is "the value is literally
what is written here".  Which is a redundant statement; 'as written' is,
after all, what literally means when used correctly :).  That makes it
a language-agnostic concept if I'm correct.

I think we will find that f strings are called f expressions, not f literals.

--David
More information about the Python-Dev mailing list