Ban (except)

It's rarely useful, because it catches all exceptions, but it doesn't let you do anything other than return `None`. You can still get the same effect with `(except [])`.

NEWS.rst

@@ -23,6 +23,7 @@ Other Breaking Changes
 * `hy-repr` uses registered functions instead of methods
 * `HyKeyword` no longer inherits from the string type and has been
   made into its own object type.
+* `(except)` is no longer allowed. Use `(except [])` instead.
 
 New Features
 ------------------------------

hy/compiler.py

@@ -908,7 +908,9 @@ class HyASTCompiler(object):
     def _compile_catch_expression(self, expr, var):
         catch = expr.pop(0)  # catch
 
-        exceptions = expr.pop(0) if expr else HyList()
+        if not expr:
+            raise HyTypeError(expr, "`%s' missing exceptions list" % catch)
+        exceptions = expr.pop(0)
 
         # exceptions catch should be either:
         # [[list of exceptions]]

tests/compilers/test_ast.py

@@ -125,11 +125,11 @@ def test_ast_bad_raise():
 
 def test_ast_good_try():
     "Make sure AST can compile valid try"
-    can_compile("(try 1 (except) (else 1))")
+    can_compile("(try 1 (except []) (else 1))")
     can_compile("(try 1 (finally 1))")
-    can_compile("(try 1 (except) (finally 1))")
+    can_compile("(try 1 (except []) (finally 1))")
     can_compile("(try 1 (except [x]) (except [y]) (finally 1))")
-    can_compile("(try 1 (except) (else 1) (finally 1))")
+    can_compile("(try 1 (except []) (else 1) (finally 1))")
     can_compile("(try 1 (except [x]) (except [y]) (else 1) (finally 1))")
 
 
@@ -142,14 +142,13 @@ def test_ast_bad_try():
     cant_compile("(try (do bla bla))")
     cant_compile("(try (do) (else 1) (else 2))")
     cant_compile("(try 1 (else 1))")
-    cant_compile("(try 1 (else 1) (except))")
-    cant_compile("(try 1 (finally 1) (except))")
-    cant_compile("(try 1 (except) (finally 1) (else 1))")
+    cant_compile("(try 1 (else 1) (except []))")
+    cant_compile("(try 1 (finally 1) (except []))")
+    cant_compile("(try 1 (except []) (finally 1) (else 1))")
 
 
 def test_ast_good_except():
     "Make sure AST can compile valid except"
-    can_compile("(try 1 (except))")
     can_compile("(try 1 (except []))")
     can_compile("(try 1 (except [Foobar]))")
     can_compile("(try 1 (except [[]]))")
@@ -161,8 +160,10 @@ def test_ast_good_except():
 def test_ast_bad_except():
     "Make sure AST can't compile invalid except"
     cant_compile("(except 1)")
+    cant_compile("(try 1 (except))")
     cant_compile("(try 1 (except 1))")
     cant_compile("(try 1 (except [1 3]))")
+    cant_compile("(try 1 (except [(f) [IOError ValueError]]))")
     cant_compile("(try 1 (except [x [FooBar] BarBar]))")
 
 

tests/native_tests/language.hy

@@ -565,13 +565,13 @@
 (defn test-exceptions []
   "NATIVE: test Exceptions"
 
-  (try (do) (except))
+  (try (do) (except []))
 
-  (try (do) (except [IOError]) (except))
+  (try (do) (except [IOError]) (except []))
 
   ; test that multiple expressions in a try get evaluated
   (setv value 0)
-  (try (+= value 1) (+= value 2)  (except [IOError]) (except))
+  (try (+= value 1) (+= value 2)  (except [IOError]) (except []))
   (assert (= value 3))
 
   ;; Test correct (raise)
@@ -606,7 +606,7 @@
   (setv passed False)
   (try
    (raise Exception)
-   (except)
+   (except [])
    (finally (setv passed True)))
   (assert passed)
 
@@ -616,7 +616,7 @@
         not-elsed True)
   (try
    (raise Exception)
-   (except)
+   (except [])
    (else (setv not-elsed False))
    (finally (setv passed True)))
   (assert passed)
@@ -662,10 +662,6 @@
    (get [1] 3)
    (except [[IndexError NameError]] (do)))
 
-  (try
-   (print foobar42ofthebaz)
-   (except))
-
   (try
    (print foobar42ofthebaz)
    (except []))
@@ -682,7 +678,7 @@
 
   (setv passed False)
   (try
-   (try (do) (except) (else (bla)))
+   (try (do) (except []) (else (bla)))
    (except [NameError] (setv passed True)))
   (assert passed)
 
@@ -709,7 +705,7 @@
     (except [IOError]
       (setv x 45))
     (else (setv x 44)))
-   (except))
+   (except []))
   (assert (= x 0))
 
   ; test that [except ...] and ("except" ...) aren't treated like (except ...),
@@ -718,7 +714,7 @@
   (try
     (+= x 1)
     ("except" [IOError]  (+= x 1))
-    (except))
+    (except []))
 
   (assert (= x 2))
 
@@ -726,7 +722,7 @@
   (try
     (+= x 1)
     [except [IOError]  (+= x 1)]
-    (except))
+    (except []))
 
   (assert (= x 2)))