Ian Kelly wrote: > […] Thomas 'PointedEars' Lahn […] wrote: >> Chris Angelico wrote: >>> […] Thomas 'PointedEars' Lahn […] wrote: >>>>> Implicit concatenation is part of the syntax, not part of the >>>>> expression evaluator. >>>> Reads like nonsense to me. >>> What do you mean? >> As I showed, string literals and consecutive tokens of string literals >> (“STRING+”) so as to do implicit concatenation *are* expressions of the >> Python grammar. Expressions are *part of* the syntax of a programming >> language. >> >> Perhaps you mean that the time when implicit concatenation is evaluated >> (compile time) differs from the time when other expressions are evaluated >> (runtime). But a) whether that is true depends on the implementation and >> b) there can be no doubt that either expression needs to be evaluated. >> So whatever you mean by “expression evaluator” has to be able to do those >> things. >> >> Which makes the statement above read like nonsense to me. > > What the grammar that you quoted from shows is that STRING+ is an > expression. The individual STRINGs of a STRING+ are not expressions, > except to the extent that they can be parsed in isolation as a > STRING+.
How did you get that idea? STRING+ means one or more consecutive STRING tokens (ignoring whitespace in-between), which means one or more consecutive string literals. A (single) string literal definitely is an expression as it can be produced with the “expr” goal symbol of the Python grammar (given there in a flavor of EBNF). > By the same token, a STRING+ is a single string literal, not > an aggregate of several. No, in the used flavour of EBNF the unquoted “+” following a goal symbol clearly means the occurrence of *at least one* of the immediately preceding symbol, meaning either one *or more than one*. <http://en.wikipedia.org/wiki/Backus%E2%80%93Naur_Form> pp. > Ancillary data point: > > >>> help(ast.literal_eval) > Safely evaluate an expression node or a string containing a Python > expression. The string or node provided may only consist of the > following Python literal structures: strings, bytes, numbers, tuples, > lists, dicts, sets, booleans, and None. > >>> ast.literal_eval('"foo" "bar"') > 'foobar' > > So the ast.literal_eval also treats this as one literal expression. What do you mean? ast.literal_eval() sees a single string value resulting from the evaluation of one string literal, by the Python compiler, that contains the representation of two consecutive string literals: '"foo" "bar"' It then does exactly what the Python compiler would do in such a case: parse this as if it were one string literal (the “implicit concatenation” I am talking about). "foo" "bar" ≡ "foobar" This was not debated. -- PointedEars Twitter: @PointedEars2 Please do not cc me. / Bitte keine Kopien per E-Mail. -- https://mail.python.org/mailman/listinfo/python-list
