Fixed wrong use of exception and ambiguous exception names

execjs/__init__.py

@@ -22,7 +22,13 @@
 '''
 from __future__ import unicode_literals, division, with_statement
 
-from execjs._exceptions import Error, RuntimeError, ProgramError, RuntimeUnavailableError
+from execjs._exceptions import (
+    Error,
+    RuntimeError,
+    ProgramError,
+    RuntimeUnavailableError,
+)
+
 import execjs._runtimes
 from execjs._external_runtime import ExternalRuntime
 from execjs._abstract_runtime import AbstractRuntime

execjs/_exceptions.py

@@ -1,18 +1,24 @@
+# Abstract base error classes
 class Error(Exception):
     pass
 
-
+# Abstract class that represents errors of runtime engine.
+# ex. Specified runtime engine is not installed, runtime engine aborted (by its bugs).
+# By the way "RuntimeError" is bad name because it is confusing with the standard exception.
 class RuntimeError(Error):
+    pass
+
+# Concrete runtime error classes
+class RuntimeUnavailableError(RuntimeError): pass
+
+class ProcessExitedWithNonZeroStatus(RuntimeError):
     def __init__(self, status, stdout, stderr):
-        Error.__init__(self, status, stdout, stderr)
+        RuntimeError.__init__(self, status, stdout, stderr)
         self.status = status
         self.stdout = stdout
         self.stderr = stderr
 
-
+# Errors due to JS script.
+# ex. Script has syntax error, executed and raised exception.
 class ProgramError(Error):
     pass
-
-
-class RuntimeUnavailableError(RuntimeError):
-    pass

execjs/_external_runtime.py

@@ -11,7 +11,12 @@
 import six
 import execjs._json2 as _json2
 import execjs._runner_sources as _runner_sources
-import execjs._exceptions as exceptions
+
+from execjs._exceptions import (
+    ProcessExitedWithNonZeroStatus,
+    ProgramError
+)
+
 from execjs._abstract_runtime import AbstractRuntime
 from execjs._abstract_runtime_context import AbstractRuntimeContext
 from execjs._misc import encode_unicode_codepoints
@@ -126,7 +131,7 @@ def _exec_with_tempfile(self, source):
 
         def _fail_on_non_zero_status(self, status, stdoutdata, stderrdata):
             if status != 0:
-                raise exceptions.RuntimeError(status=status, stdout=stdoutdata, stderr=stderrdata)
+                raise ProcessExitedWithNonZeroStatus(status=status, stdout=stdoutdata, stderr=stderrdata)
 
         def _compile(self, source):
             runner_source = self._runtime._runner_source
@@ -151,18 +156,15 @@ def _extract_result(self, output):
             output = output.replace("\r\n", "\n").replace("\r", "\n")
             output_last_line = output.split("\n")[-2]
 
-            if not output_last_line:
-                raise exceptions.ProgramError
-            else:
-                ret = json.loads(output_last_line)
-                if len(ret) == 1:
-                    ret = [ret[0], None]
-                status, value = ret
+            ret = json.loads(output_last_line)
+            if len(ret) == 1:
+                ret = [ret[0], None]
+            status, value = ret
 
             if status == "ok":
                 return value
             else:
-                raise exceptions.ProgramError(value)
+                raise ProgramError(value)
 
 
 def _is_windows():

execjs/_pyv8runtime.py

@@ -53,7 +53,7 @@ def _exec_(self, source):
                 try:
                     script = engine.compile(source)
                 except js_errors as e:
-                    raise exceptions.RuntimeError(e)
+                    raise exceptions.ProgramError(e)
                 try:
                     value = script.run()
                 except js_errors as e: