error in syntax description for comprehensions?
tjreedy at udel.edu
Thu Mar 30 20:43:21 EDT 2017
On 3/30/2017 4:57 PM, Boylan, Ross wrote:
> describes the syntax for comprehensions as
> comprehension ::= expression comp_for
> comp_for ::= [ASYNC] "for" target_list "in" or_test [comp_iter]
> comp_iter ::= comp_for | comp_if
> comp_if ::= "if" expression_nocond [comp_iter]
> Is the comp_for missing an argument after "in"?
The or_test *is* the 'argument'.
> One has to follow the definition of or_test and its components,
> but I can't find anything that results to a single variable
> or expression.
An or_test *is* a single expression. Like all python expressions, it
evaluates to a python object. In this case, the object is passed to
iter() and so the object must be an iterable.
>>> a, b = None, range(3)
>>> a or b
>>> for i in a or b: print(i)
Terry Jan Reedy
More information about the Python-list