Disallow "import mod.submod as m", because the result is ambiguous. Does it

load mod.submod as m, or mod as m ? Both can be achieved differently, and
unambiguously. Also attempt to document this restriction (editor
appreciated!)

Note that this is an artificial check during compile, because incorporating
this in the grammar is hard, and then adjusting the compiler to do the right
thing with the right nodes is harder.

diff --git a/Doc/ref/ref6.tex b/Doc/ref/ref6.tex
index 008cf1c436e21537a261ab9d56498823e9a896a0..3f21479528f97c38d699b8a41107b7fd16664cf4 100644 (file)
--- a/Doc/ref/ref6.tex
+++ b/Doc/ref/ref6.tex
@@ -498,7 +498,12 @@ begin.
 The first form of \keyword{import} statement binds the module name in the
 local namespace to the module object, and then goes on to import the
 next identifier, if any.  If the module name is followed by \keyword{as},
-the name following \keyword{as} is used as the local name for the module. 
+the name following \keyword{as} is used as the local name for the module. To
+avoid confusion, you cannot import sub-modules 'as' a different
+local name. So 'import module as m' is legal, but 'import module.submod as
+s' is not. The latter should be written as 'from module import submod as s',
+see below.
+
 The \keyword{from} form does not bind the module name: it goes through the
 list of identifiers, looks each one of them up in the module found in step
 (1), and binds the name in the local namespace to the object thus found. 

diff --git a/Python/compile.c b/Python/compile.c
index 47445d067911738e9b6eeaa0f4c6ed08f55054c8..73167909baa2179746710b8d7ceaede487dd22c1 100644 (file)
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -2139,7 +2139,8 @@ com_import_stmt(struct compiling *c, node *n)
                        com_addopname(c, IMPORT_NAME, CHILD(subn, 0));
                        com_push(c, 1);
                        if (NCH(subn) > 1) {
-                               if (strcmp(STR(CHILD(subn, 1)), "as") != 0) {
+                               if (strcmp(STR(CHILD(subn, 1)), "as") != 0 ||
+                                   NCH(CHILD(subn, 0)) > 1) {
                                        com_error(c, PyExc_SyntaxError,
                                                  "invalid syntax");
                                        return;