gpython: Reorganize options parsing

Reorganize parsiong of command line options so that first all options are
parsed in a loop, and only after that a module/file/command is executed.

This is needed as preparatory step for next patch: there we'll add
support for -W, and `-W arg` can be given multiple times and has to be
processed multiple times by creating multiple corresponding warning
filters. Because those warning filters has to be applied uniformly to
all 4 codepaths of execution phase (-m/-c/file/interactive console), it
makes sense to move execution phase to after options parsing and inject
common runtime preparatory steps right before that.

This logic generally applies not only to -W, but to all other python
options - e.g. -Q,-u,...

gpython/__init__.py

@@ -49,30 +49,9 @@ def pymain(argv):
     from os.path import dirname
     from six.moves import input as raw_input
 
-    # interactive console
-    if not argv:
-        sys.argv = ['']
-        sys.path.insert(0, '')  # cwd
-
-        # like code.interact() but with overridden console.raw_input _and_
-        # readline imported (code.interact mutually excludes those two).
-        try:
-            import readline # enable interactive editing
-        except ImportError:
-            pass
-
-        console = code.InteractiveConsole()
-        def _(prompt):
-            # python behaviour: don't print '>>>' if stdin is not a tty
-            # (builtin raw_input always prints prompt)
-            if not sys.stdin.isatty():
-                prompt=''
-            return raw_input(prompt)
-        console.raw_input = _
-
-        console.interact()
-        return
+    run = None          # function to run according to -c/-m/file/interactive
 
+    while len(argv) > 0:
         # -V / --version
         if argv[0] in ('-V', '--version'):
             ver = []
@@ -104,7 +83,7 @@ def pymain(argv):
                 ver = sys.version
 
             print(ver, file=sys.stderr)
-
+            return
 
         # -c command
         elif argv[0].startswith('-c'):
@@ -115,12 +94,13 @@ def pymain(argv):
                 argv = argv[1:]
             sys.argv = ['-c'] + argv # python leaves '-c' as argv[0]
             sys.path.insert(0, '')   # cwd
-
+            def run():
                 # exec with the same globals `python -c ...` does
                 g = {'__name__':    '__main__',
                      '__doc__':     None,
                      '__package__': None}
                 six.exec_(cmd, g)
+            break
 
         # -m module
         elif argv[0].startswith('-m'):
@@ -129,11 +109,13 @@ def pymain(argv):
             if mod == '':
                 mod  = argv[0]
                 argv = argv[1:]
-        # search sys.path for module and run corresponding .py file as script
             sys.argv = [mod] + argv
             sys.path.insert(0, '')  # cwd
+            def run():
+                # search sys.path for module and run corresponding .py file as script
                 runpy.run_module(mod, init_globals={'__doc__': None},
                                  run_name='__main__', alter_sys=True)
+            break
 
         elif argv[0].startswith('-'):
             print("unknown option: '%s'" % argv[0], file=sys.stderr)
@@ -144,7 +126,7 @@ def pymain(argv):
             sys.argv = argv
             filepath = argv[0]
             sys.path.insert(0, dirname(filepath))
-
+            def run():
                 # exec with same globals `python file.py` does
                 # XXX use runpy.run_path() instead?
                 g = {'__name__':    '__main__',
@@ -152,8 +134,35 @@ def pymain(argv):
                      '__doc__':     None,
                      '__package__': None}
                 _execfile(filepath, g)
+            break
+
+    # interactive console
+    if run is None:
+        sys.argv = ['']
+        sys.path.insert(0, '')  # cwd
+
+        def run():
+            # like code.interact() but with overridden console.raw_input _and_
+            # readline imported (code.interact mutually excludes those two).
+            try:
+                import readline # enable interactive editing
+            except ImportError:
+                pass
+
+            console = code.InteractiveConsole()
+            def _(prompt):
+                # python behaviour: don't print '>>>' if stdin is not a tty
+                # (builtin raw_input always prints prompt)
+                if not sys.stdin.isatty():
+                    prompt=''
+                return raw_input(prompt)
+            console.raw_input = _
+
+            console.interact()
+
+    # execute -m/-c/file/interactive
+    run()
 
-    return
 
 # execfile was removed in py3
 def _execfile(path, globals=None, locals=None):