Proposed new syntax

[Steven D'Aprano]

On Sun, 13 Aug 2017 21:06:08 -0700, Rustom Mody wrote:


> Here's a bunch of different ways in which a mapping comprehension could
> be implemented:

Not in Python they couldn't be, since Python promises deterministic, 
first-to-last evaluation in the same order as the equivalent for-loop.


    When a list comprehension is supplied, it consists of a single
    expression followed by at least one for clause and zero or more for
    or if clauses. In this case, the elements of the new list are those
    that would be produced by considering each of the for or if clauses a
    block, nesting from left to right, and evaluating the expression to
    produce a list element each time the innermost block is reached.


https://docs.python.org/2/reference/expressions.html#list-displays

The docs for Python 3 are equivalent:

https://docs.python.org/3/reference/expressions.html#displays-for-lists-
sets-and-dictionaries

See also the tutorial, which says more or less the same thing:

https://docs.python.org/2/tutorial/datastructures.html#list-comprehensions




-- 
“You are deluded if you think software engineers who can't write 
operating systems or applications without security holes, can write 
virtualization layers without security holes.” —Theo de Raadt