Implement Python 2 exec

The implementation of `hy.core.language.exec` draws code from the `exec_` function in commit f574c7be6ebc80041ef58ca29588f310248ebed4 of the library Six, which is copyright 2010–2017 Benjamin Peterson and licensed under the Expat license.

NEWS

@@ -23,6 +23,7 @@ Changes from 0.13.0
      mistaken for shebang lines
    * Fixed a bug where REPL history wasn't saved if you quit the REPL with
      `(quit)` or `(exit)`
+   * `exec` now works under Python 2
 
 Changes from 0.12.1
 

docs/conf.py

@@ -5,6 +5,8 @@
 import re, os, sys, time, cgi
 sys.path.append(os.path.abspath(".."))
 
+extensions = ['sphinx.ext.intersphinx']
+
 from get_version import __version__ as hy_version
 # Read the Docs might dirty its checkout, so strip the dirty flag.
 hy_version = re.sub('[+.]dirty\Z', '', hy_version)
@@ -48,3 +50,7 @@ html_show_sphinx = False
 
 html_context = dict(
     hy_descriptive_version = hy_descriptive_version)
+
+intersphinx_mapping = dict(
+    py2 = ('https://docs.python.org/2', None),
+    py  = ('https://docs.python.org/3', None))

docs/language/core.rst

@@ -281,6 +281,19 @@ otherwise ``False``. Return ``True`` if *coll* is empty.
    True
 
 
+.. _exec-fn:
+
+exec
+----
+
+Equivalent to Python 3's built-in function :py:func:`exec`.
+
+.. code-block:: clj
+
+    => (exec "print(a + b)" {"a" 1} {"b" 2})
+    3
+
+
 .. _float?-fn:
 
 float?

hy/compiler.py

@@ -778,6 +778,19 @@ class HyASTCompiler(object):
     def compile_unpack_mapping(self, expr):
         raise HyTypeError(expr, "`unpack-mapping` isn't allowed here")
 
+    @builds_if("exec*", not PY3)
+    # Under Python 3, `exec` is a function rather than a statement type, so Hy
+    # doesn't need a special form for it.
+    @checkargs(min=1, max=3)
+    def compile_exec(self, expr):
+        expr.pop(0)
+        return ast.Exec(
+            lineno=expr.start_line,
+            col_offset=expr.start_column,
+            body=self.compile(expr.pop(0)).force_expr,
+            globals=self.compile(expr.pop(0)).force_expr if expr else None,
+            locals=self.compile(expr.pop(0)).force_expr if expr else None)
+
     @builds("do")
     def compile_do(self, expression):
         expression.pop(0)

hy/core/language.hy

@@ -117,6 +117,24 @@
    range range
    zip zip))
 
+(if-python2
+  (defn exec [$code &optional $globals $locals]
+    "Execute Python code.
+
+    The parameter names contain weird characters to discourage calling this
+    function with keyword arguments, which isn't supported by Python 3's
+    `exec`."
+    (if
+      (none? $globals) (do
+        (setv frame (._getframe sys (int 1)))
+        (try
+          (setv $globals frame.f_globals  $locals frame.f_locals)
+          (finally (del frame))))
+      (none? $locals)
+        (setv $locals $globals))
+    (exec* $code $globals $locals))
+  (def exec exec))
+
 ;; infinite iterators
 (def
   count itertools.count
@@ -461,8 +479,8 @@
 (def *exports*
   '[*map accumulate butlast calling-module-name chain coll? combinations
     comp complement compress cons cons? constantly count cycle dec distinct
-    disassemble drop drop-last drop-while empty? eval even? every? first filter
+    disassemble drop drop-last drop-while empty? eval even? every? exec first
-    flatten float? fraction gensym group-by identity inc input instance?
+    filter flatten float? fraction gensym group-by identity inc input instance?
     integer integer? integer-char? interleave interpose islice iterable?
     iterate iterator? juxt keyword keyword? last list* macroexpand
     macroexpand-1 map merge-with multicombinations name neg? none? nth

tests/compilers/test_ast.py

@@ -593,3 +593,27 @@ def test_setv_builtins():
 def test_lots_of_comment_lines():
     # https://github.com/hylang/hy/issues/1313
     can_compile(1000 * ";\n")
+
+
+def test_exec_star():
+
+    code = can_compile('(exec* "print(5)")').body[0]
+    assert type(code) == (ast.Expr if PY3 else ast.Exec)
+    if not PY3:
+        assert code.body.s == "print(5)"
+        assert code.globals is None
+        assert code.locals is None
+
+    code = can_compile('(exec* "print(a)" {"a" 3})').body[0]
+    assert type(code) == (ast.Expr if PY3 else ast.Exec)
+    if not PY3:
+        assert code.body.s == "print(a)"
+        assert code.globals.keys[0].s == "a"
+        assert code.locals is None
+
+    code = can_compile('(exec* "print(a + b)" {"a" "x"} {"b" "y"})').body[0]
+    assert type(code) == (ast.Expr if PY3 else ast.Exec)
+    if not PY3:
+        assert code.body.s == "print(a + b)"
+        assert code.globals.keys[0].s == "a"
+        assert code.locals.keys[0].s == "b"

tests/native_tests/core.hy

@@ -170,6 +170,49 @@
   (assert-false (every? even? [2 4 5]))
   (assert-true (every? even? [])))
 
+(setv globalvar 1)
+(defn test-exec []
+  (setv localvar 1)
+  (setv code "
+result['localvar in locals'] = 'localvar' in locals()
+result['localvar in globals'] = 'localvar' in globals()
+result['globalvar in locals'] = 'globalvar' in locals()
+result['globalvar in globals'] = 'globalvar' in globals()
+result['x in locals'] = 'x' in locals()
+result['x in globals'] = 'x' in globals()
+result['y in locals'] = 'y' in locals()
+result['y in globals'] = 'y' in globals()")
+
+  (setv result {})
+  (exec code)
+  (assert-true (get result "localvar in locals"))
+  (assert-false (get result "localvar in globals"))
+  (assert-false (get result "globalvar in locals"))
+  (assert-true (get result "globalvar in globals"))
+  (assert-false (or
+    (get result "x in locals") (get result "x in globals")
+    (get result "y in locals") (get result "y in globals")))
+
+  (setv result {})
+  (exec code {"x" 1 "result" result})
+  (assert-false (or
+    (get result "localvar in locals") (get result "localvar in globals")
+    (get result "globalvar in locals") (get result "globalvar in globals")))
+  (assert-true (and
+    (get result "x in locals") (get result "x in globals")))
+  (assert-false (or
+    (get result "y in locals") (get result "y in globals")))
+
+  (setv result {})
+  (exec code {"x" 1 "result" result} {"y" 1})
+  (assert-false (or
+    (get result "localvar in locals") (get result "localvar in globals")
+    (get result "globalvar in locals") (get result "globalvar in globals")))
+  (assert-false (get result "x in locals"))
+  (assert-true (get result "x in globals"))
+  (assert-true (get result "y in locals"))
+  (assert-false (get result "y in globals")))
+
 (defn test-filter []
   "NATIVE: testing the filter function"
   (setv res (list (filter pos? [ 1 2 3 -4 5])))