Changed gsapi.py to raise exceptions instead of returning error number

gsapi.py:
    Generate exceptions instead of returning error codes.
    Added python versions of gs_error_* codes.

examples.py:
    Updated to match new API.
    Re-raise import error if 'import gsapi' fails.
    Patched up calls of run_gpdl() to pass in_filename because passing None
    caused underlying C to return an error.
    Marked as executable.
    Look for input files relative to top of ghospdl checkout (found using
    __file__).

2 files changed, 219 insertions, 221 deletions

diff --git a/demos/python/examples.py b/demos/python/examples.py
index 296a0805a..d5c8b6adb 100644..100755
--- a/demos/python/examples.py
+++ b/demos/python/examples.py
@@ -1,3 +1,4 @@
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 """
 Created on Tue Jul 21 10:05:07 2020
@@ -8,93 +9,35 @@ Example use of gsapi for various tasks.
 
 try:
     import gsapi
-except Exception as err:
+except Exception:
     print('Failure to import gsapi. Check shared library path')
-    print(err.args)
+    raise
 
-def run_gpdl(params, path):
-
-    try:
-        e, instance = gsapi.gsapi_new_instance(0)
-        if e:
-            raise Warning('gsapi_new_instance failure')
-    except Exception as err:
-        print(err.args)
-        return
-
-    try:
-        e = gsapi.gsapi_set_arg_encoding(instance, gsapi.GS_ARG_ENCODING_UTF8)
-        if e:
-            raise Warning('gsapi_set_arg_encoding failure')
-
-        if path != None:
-            e = gsapi.gsapi_add_control_path(instance, gsapi.GS_PERMIT_FILE_READING, path)
-            if e:
-                raise Warning('gsapi_add_control_path failure')
+import os
 
-        e = gsapi.gsapi_init_with_args(instance, params)
-        if e:
-            raise Warning('gsapi_init_with_args failure')
-
-    except Exception as err:
-        print(err.args)
-        return
+ghostpdl_root = os.path.abspath('%s/../../..' % __file__)
+print('ghostpdl_root=%s' % ghostpdl_root)
 
+def run_gpdl(params, path):
+    instance = gsapi.gsapi_new_instance(0)
+    gsapi.gsapi_set_arg_encoding(instance, gsapi.GS_ARG_ENCODING_UTF8)
+    gsapi.gsapi_add_control_path(instance, gsapi.GS_PERMIT_FILE_READING, path)
+    gsapi.gsapi_init_with_args(instance, params)
     end_gpdl(instance)
-    return
 
 def init_gpdl(params):
-
-    try:
-        e, instance = gsapi.gsapi_new_instance(0)
-        if e:
-            raise Warning('gsapi_new_instance failure')
-    except Exception as err:
-        print(err.args)
-        return None
-
-    try:
-        e = gsapi.gsapi_set_arg_encoding(instance, gsapi.GS_ARG_ENCODING_UTF8)
-        if e:
-            raise Warning('gsapi_set_arg_encoding failure')
-
-        e = gsapi.gsapi_init_with_args(instance, params)
-        if e:
-            raise Warning('gsapi_init_with_args failure')
-
-    except Exception as err:
-        print(err.args)
-        return None
-
+    instance = gsapi.gsapi_new_instance(0)
+    gsapi.gsapi_set_arg_encoding(instance, gsapi.GS_ARG_ENCODING_UTF8)
+    gsapi.gsapi_init_with_args(instance, params)
     return instance
 
 def run_file(instance, filename):
-
-    try:
-        (e, exitcode) = gsapi.gsapi_run_file(instance, filename, None)
-        if e:
-            raise Warning('gsapi_run_file failure')
-
-    except Exception as err:
-        print(err.args)
-
-    return
+    exitcode = gsapi.gsapi_run_file(instance, filename, None)
+    return exitcode
 
 def end_gpdl(instance):
-
-    try:
-        e = gsapi.gsapi_exit(instance)
-        if e:
-            raise Warning('gsapi_exit failure')
-    
-        e = gsapi.gsapi_delete_instance(instance)
-        if e:
-            raise Warning('gsapi_delete_instance failure')
-
-    except Exception as err:
-        print(err.args)
-
-    return
+    gsapi.gsapi_exit(instance)
+    gsapi.gsapi_delete_instance(instance)
 
 # run multiple files through same instance
 def multiple_files():
@@ -104,34 +47,32 @@ def multiple_files():
     params =['gs', '-dNOPAUSE', '-dBATCH', '-sDEVICE=pngalpha',
              '-r72', '-o', out_filename]
     instance = init_gpdl(params)
-    run_file(instance, '../../examples/tiger.eps')
-    run_file(instance, '../../examples/snowflak.ps')
-    run_file(instance, '../../examples/annots.pdf')
+    run_file(instance, '%s/examples/tiger.eps' % ghostpdl_root)
+    run_file(instance, '%s/examples/snowflak.ps' % ghostpdl_root)
+    run_file(instance, '%s/examples/annots.pdf' % ghostpdl_root)
 
     end_gpdl(instance)
 
 # Extract text from source file
 def extract_text():
 
-    in_filename = '../../examples/alphabet.ps'
+    in_filename = '%s/examples/alphabet.ps' % ghostpdl_root
     out_filename = 'alphabet.txt'
     print('Extracting text from %s to %s' % (in_filename, out_filename))
 
     params =['gs', '-dNOPAUSE', '-dBATCH','-sDEVICE=txtwrite',
              '-dTextFormat=3','-o', out_filename, '-f', in_filename]
-    run_gpdl(params, None)
-
-    return
+    run_gpdl(params, in_filename)
 
 # Perform different color conversions on text, graphic, and image content
 # through the use of different destination ICC profiles
 def object_dependent_color_conversion():
 
-    in_filename = '../../examples/text_graph_image_cmyk_rgb.pdf'
+    in_filename = '%s/examples/text_graph_image_cmyk_rgb.pdf' % ghostpdl_root
     out_filename = 'rendered_profile.tif'
-    image_icc = '../../toolbin/color/icc_creator/effects/cyan_output.icc'
-    graphic_icc = '../../toolbin/color/icc_creator/effects/magenta_output.icc'
-    text_icc = '../../toolbin/color/icc_creator/effects/yellow_output.icc'
+    image_icc = '%s/toolbin/color/icc_creator/effects/cyan_output.icc' % ghostpdl_root
+    graphic_icc = '%s/toolbin/color/icc_creator/effects/magenta_output.icc' % ghostpdl_root
+    text_icc = '%s/toolbin/color/icc_creator/effects/yellow_output.icc' % ghostpdl_root
     print('Object dependent color conversion on %s to %s' % (in_filename, out_filename))
 
     params =['gs', '-dNOPAUSE', '-dBATCH', '-sDEVICE=tiff32nc',
@@ -143,15 +84,13 @@ def object_dependent_color_conversion():
     # Include ICC profile location to readable path
     run_gpdl(params, '../../toolbin/color/icc_creator/effects/')
 
-    return
-
 # Perform different color conversions on text, graphic, and image content
 # through the use of different rendering intents
 def object_dependent_rendering_intent():
 
-    in_filename = '../../examples/text_graph_image_cmyk_rgb.pdf'
+    in_filename = '%s/examples/text_graph_image_cmyk_rgb.pdf' % ghostpdl_root
     out_filename = 'rendered_intent.tif'
-    output_icc_profile = '../../toolbin/color/src_color/cmyk_des_renderintent.icc'
+    output_icc_profile = '%s/toolbin/color/src_color/cmyk_des_renderintent.icc' % ghostpdl_root
     print('Object dependent rendering intents on %s to %s' % (in_filename, out_filename))
 
     params =['gs', '-dNOPAUSE', '-dBATCH', '-sDEVICE=tiff32nc',
@@ -163,85 +102,55 @@ def object_dependent_rendering_intent():
     # Include ICC profile location to readable path
     run_gpdl(params, '../../toolbin/color/src_color/')
 
-    return
-
 # Distill
 def distill():
 
-    in_filename = '../../examples/tiger.eps'
+    in_filename = '%s/examples/tiger.eps' % ghostpdl_root
     out_filename = 'tiger.pdf'
     print('Distilling %s to %s' % (in_filename, out_filename))
 
     params =['gs', '-dNOPAUSE', '-dBATCH', '-sDEVICE=pdfwrite',
              '-o', out_filename, '-f', in_filename]
-    run_gpdl(params, None)
-
-    return
+    run_gpdl(params, in_filename)
 
 # Transparency in Postscript
 def trans_ps():
 
-    in_filename = '../../examples/transparency_example.ps'
+    in_filename = '%s/examples/transparency_example.ps' % ghostpdl_root
     out_filename = 'transparency.png'
     print('Rendering Transparency PS file %s to %s' % (in_filename, out_filename))
 
     params =['gs', '-dNOPAUSE', '-dBATCH', '-sDEVICE=pngalpha',
              '-dALLOWPSTRANSPARENCY', '-o', out_filename, '-f', in_filename]
-    run_gpdl(params, None)
-
-    return
+    run_gpdl(params, in_filename)
 
 # Run string to feed chunks
 def run_string():
 
     f = None
     size = 1024;
-    in_filename = '../../examples/tiger.eps'
+    in_filename = '%s/examples/tiger.eps' % ghostpdl_root
     out_filename = 'tiger_byte_fed.png'
     params =['gs', '-dNOPAUSE', '-dBATCH', '-sDEVICE=pngalpha',
               '-o', out_filename]
 
-    try:
-        e, instance = gsapi.gsapi_new_instance(0)
-        if e:
-            raise Warning('gsapi_new_instance failure')
-    except Exception as err:
-        print(err.args)
-        return
-
-    try:
-        e = gsapi.gsapi_set_arg_encoding(instance, gsapi.GS_ARG_ENCODING_UTF8)
-        if e:
-            raise Warning('gsapi_set_arg_encoding failure')
-    
-        e = gsapi.gsapi_init_with_args(instance, params)
-        if e:
-            raise Warning('gsapi_init_with_args failure')
-
-        [e, exitcode] = gsapi.gsapi_run_string_begin(instance, 0)
-        if e:
-            raise Warning('gsapi_run_string_begin failure')
-
-        f = open(in_filename,"rb")
+    instance = gsapi.gsapi_new_instance(0)
+
+    gsapi.gsapi_set_arg_encoding(instance, gsapi.GS_ARG_ENCODING_UTF8)
+    gsapi.gsapi_init_with_args(instance, params)
+
+    exitcode = gsapi.gsapi_run_string_begin(instance, 0)
+
+    with open(in_filename,"rb") as f:
         while True:
             data = f.read(size)
             if not data:
                 break
-            [e, exitcode] = gsapi.gsapi_run_string_continue(instance, data, 0)
-            if e:
-                raise Warning('gsapi_run_string_continue failure')
-
-        [e, exitcode] = gsapi.gsapi_run_string_end(instance, 0)
-        if e:
-            raise Warning('gsapi_run_string_end failure')
+            exitcode = gsapi.gsapi_run_string_continue(instance, data, 0)
 
-    except Exception as err:
-        print(err.args)
+    exitcode = gsapi.gsapi_run_string_end(instance, 0)
 
     end_gpdl(instance)
-    if f != None:
-        f.close()
-    return
 
 
 # Examples
@@ -259,4 +168,4 @@ print('***********Multiple files********')
 multiple_files()
 print('***********Run string********')
 run_string()
-wait = input("press enter to exit")
\ No newline at end of file
+wait = input("press enter to exit")
diff --git a/demos/python/gsapi.py b/demos/python/gsapi.py
index 5d656606c..6feff2461 100755
--- a/demos/python/gsapi.py
+++ b/demos/python/gsapi.py
@@ -7,9 +7,11 @@ Overview:
 
     All functions have the same name as the C function that they wrap.
 
-    All functions return an integer error code unless otherwise stated. [The
-    exceptions are usually for out-parameters, which are returned directly as
-    part of a tuple.]
+    Functions raise a GSError exception if the underlying function returned a
+    negative error code.
+
+    Functions that don't have out-params return None. Out-params are returned
+    directly (using tuples if there are more than one).
 
     See examples.py for sample usage.
 
@@ -18,8 +20,7 @@ Usage:
     make sodebug
     LD_LIBRARY_PATH=sodebugbin ./demos/python/gsapi.py
 
-    On Windows perform Release build (x64 or Win32).  Select
-    appropriate DLL to use below.
+    On Windows perform Release build (x64 or Win32).
 
 Requirements:
 
@@ -61,6 +62,15 @@ else:
     raise Exception('Unrecognised platform.system()=%s' % platform.system())
 
 
+class GSError(Exception):
+    def __init__(self, gs_error):
+        self.gs_error = gs_error
+    def __str__(self):
+        return 'Ghostscript exception %i: %s' % (
+                self.gs_error,
+                _gs_error_text(self.gs_error),
+                )
+
 class gsapi_revision_t:
     def __init__(self, product, copyright, revision, revisiondate):
         self.product = product
@@ -83,15 +93,15 @@ def gsapi_revision():
     # strings.]
     _r = _gsapi_revision_t()
     e = _libgs.gsapi_revision(ctypes.byref(_r), ctypes.sizeof(_r))
-    if e:
-        return e, None
+    if e < 0:
+        raise GSError(e)
     r = gsapi_revision_t(
             _r.product.decode('utf-8'),
             _r.copyright.decode('utf-8'),
             _r.revision,
             _r.revisiondate,
             )
-    return e, r
+    return r
 
 
 def gsapi_new_instance(caller_handle):
@@ -99,13 +109,19 @@ def gsapi_new_instance(caller_handle):
     Returns (e, instance).
     '''
     instance = ctypes.c_void_p()
-    e = _libgs.gsapi_new_instance(ctypes.byref(instance), ctypes.c_void_p(caller_handle))
-    return e, instance
+    e = _libgs.gsapi_new_instance(
+            ctypes.byref(instance),
+            ctypes.c_void_p(caller_handle),
+            )
+    if e < 0:
+        raise GSError(e)
+    return instance
 
 
 def gsapi_delete_instance(instance):
     e = _libgs.gsapi_delete_instance(instance)
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 def gsapi_set_stdio(instance, stdin_fn, stdout_fn, stderr_fn):
@@ -146,20 +162,20 @@ def gsapi_set_stdio(instance, stdin_fn, stdout_fn, stderr_fn):
     stderr_fn2 = make_out(stderr_fn)
     stdin_fn2  = make_in(stdin_fn)
     e = _libgs.gsapi_set_stdio(instance, stdout_fn2, stdout_fn2, stdout_fn2)
-    if not e:
-        # Need to keep references to call-back functions.
-        global _gsapi_set_stdio_refs
-        _gsapi_set_stdio_refs = stdin_fn2, stdout_fn2, stderr_fn2
-    return e
+    if e < 0:
+        raise GSError(e)
+    # Need to keep references to call-back functions.
+    global _gsapi_set_stdio_refs
+    _gsapi_set_stdio_refs = stdin_fn2, stdout_fn2, stderr_fn2
 
 
 def gsapi_set_poll(instance, poll_fn):
     poll_fn2 = _poll_fn(poll_fn)
     e = _libgs.gsapi_set_poll(instance, poll_fn2)
-    if not e:
-        global _gsapi_set_poll_refs
-        _gsapi_set_poll_refs = poll_fn2
-    return e
+    if e < 0:
+        raise GSError(e)
+    global _gsapi_set_poll_refs
+    _gsapi_set_poll_refs = poll_fn2
 
 
 class display_callback:
@@ -208,11 +224,11 @@ def gsapi_set_display_callback(instance, callback):
         setattr(callback2, name, value2)
 
     e = _libgs.gsapi_set_display_callback(instance, ctypes.byref(callback2))
-    if not e:
-        # Ensure that we keep references to callbacks.
-        global _gsapi_set_display_callback_refs
-        _gsapi_set_display_callback_refs = callback2
-    return e
+    if e < 0:
+        raise GSError(e)
+    # Ensure that we keep references to callbacks.
+    global _gsapi_set_display_callback_refs
+    _gsapi_set_display_callback_refs = callback2
 
 
 def gsapi_set_default_device_list(instance, list_):
@@ -221,7 +237,8 @@ def gsapi_set_default_device_list(instance, list_):
     assert isinstance(list_, str)
     list_2 = list_.encode('utf-8')
     e = _libgs.gsapi_set_default_device_list(instance, list_2, len(list_))
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 def gsapi_get_default_device_list(instance):
@@ -237,9 +254,9 @@ def gsapi_get_default_device_list(instance):
             ctypes.byref(list_),
             ctypes.byref(len_),
             )
-    if e:
-        return e, ''
-    return e, list_[:len_.value].decode('latin-1')
+    if e < 0:
+        raise GSError(e)
+    return list_[:len_.value].decode('latin-1')
 
 
 GS_ARG_ENCODING_LOCAL = 0
@@ -254,15 +271,15 @@ def gsapi_set_arg_encoding(instance, encoding):
             GS_ARG_ENCODING_UTF16LE,
             )
     e = _libgs.gsapi_set_arg_encoding(instance, encoding)
-    if not e:
-        if encoding == GS_ARG_ENCODING_LOCAL:
-            # This is probably wrong on Windows.
-            _encoding = 'utf-8'
-        elif encoding == GS_ARG_ENCODING_UTF8:
-            _encoding = 'utf-8'
-        elif encoding == GS_ARG_ENCODING_UTF16LE:
-            _encoding = 'utf-16-le'
-    return e
+    if e < 0:
+        raise GSError(e)
+    if encoding == GS_ARG_ENCODING_LOCAL:
+        # This is probably wrong on Windows.
+        _encoding = 'utf-8'
+    elif encoding == GS_ARG_ENCODING_UTF8:
+        _encoding = 'utf-8'
+    elif encoding == GS_ARG_ENCODING_UTF16LE:
+        _encoding = 'utf-16-le'
 
 
 def gsapi_init_with_args(instance, args):
@@ -279,7 +296,8 @@ def gsapi_init_with_args(instance, args):
     argv[argc] = None
 
     e = _libgs.gsapi_init_with_args(instance, argc, argv)
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 def gsapi_run_string_begin(instance, user_errors):
@@ -288,7 +306,9 @@ def gsapi_run_string_begin(instance, user_errors):
     '''
     pexit_code = ctypes.c_int()
     e = _libgs.gsapi_run_string_begin(instance, user_errors, ctypes.byref(pexit_code))
-    return e, pexit_code.value
+    if e < 0:
+        raise GSError(e)
+    return pexit_code.value
 
 
 def gsapi_run_string_continue(instance, str_, user_errors):
@@ -296,7 +316,9 @@ def gsapi_run_string_continue(instance, str_, user_errors):
     <str_> should be either a python string or a bytes object. If the former,
     it is converted into a bytes object using utf-8 encoding.
 
-    Returns (e, exit_code).
+    We don't raise exception for gs_error_NeedInput.
+
+    Returns exit_code.
     '''
     if isinstance(str_, str):
         str_ = str_.encode('utf-8')
@@ -309,7 +331,12 @@ def gsapi_run_string_continue(instance, str_, user_errors):
             user_errors,
             ctypes.byref(pexit_code),
             )
-    return e, pexit_code.value
+    if e == gs_error_NeedInput.num:
+        # This is normal, so we don't raise.
+        pass
+    elif e < 0:
+        raise GSError(e)
+    return pexit_code.value
 
 
 def gsapi_run_string_end(instance, user_errors):
@@ -322,7 +349,9 @@ def gsapi_run_string_end(instance, user_errors):
             user_errors,
             ctypes.byref(pexit_code),
             )
-    return e, pexit_code.value
+    if e < 0:
+        raise GSError(e)
+    return pexit_code.value
 
 
 def gsapi_run_string_with_length(instance, str_, length, user_errors):
@@ -332,7 +361,9 @@ def gsapi_run_string_with_length(instance, str_, length, user_errors):
 
     Returns (e, exit_code).
     '''
-    return gsapi_run_string(instance, str_[:length], user_errors)
+    e = gsapi_run_string(instance, str_[:length], user_errors)
+    if e < 0:
+        raise GSError(e)
 
 
 def gsapi_run_string(instance, str_, user_errors):
@@ -354,7 +385,9 @@ def gsapi_run_string(instance, str_, user_errors):
             user_errors,
             ctypes.byref(pexit_code),
             )
-    return e, pexit_code.value
+    if e < 0:
+        raise GSError(e)
+    return pexit_code.value
 
 
 def gsapi_run_file(instance, filename, user_errors):
@@ -366,12 +399,15 @@ def gsapi_run_file(instance, filename, user_errors):
     pexit_code = ctypes.c_int()
     filename2 = filename.encode(_encoding)
     e = _libgs.gsapi_run_file(instance, filename2, user_errors, ctypes.byref(pexit_code))
-    return e, pexit_code.value
+    if e < 0:
+        raise GSError(e)
+    return pexit_code.value
 
 
 def gsapi_exit(instance):
     e = _libgs.gsapi_exit(instance)
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 gs_spt_invalid = -1
@@ -408,7 +444,8 @@ def gsapi_set_param(instance, param, value):
     else:
         assert 0, 'unrecognised type: %s' % type(value)
     e = _libgs.gsapi_set_param(instance, type2, param2, value2)
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 GS_PERMIT_FILE_READING = 0
@@ -421,7 +458,8 @@ def gsapi_add_control_path(instance, type_, path):
     # <path> to be encoded in encoding set by gsapi_set_arg_encoding().]
     path2 = path.encode(_encoding)
     e = _libgs.gsapi_add_control_path(instance, type_, path2)
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 def gsapi_remove_control_path(instance, type_, path):
@@ -429,28 +467,93 @@ def gsapi_remove_control_path(instance, type_, path):
     # <path> to be encoded in encoding set by gsapi_set_arg_encoding().]
     path2 = path.encode(_encoding)
     e = _libgs.gsapi_remove_control_path(instance, type_, path2)
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 def gsapi_purge_control_paths(instance, type_):
     e = _libgs.gsapi_purge_control_paths(instance, type_)
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 def gsapi_activate_path_control(instance, enable):
     e = _libgs.gsapi_activate_path_control(instance, enable)
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 def gsapi_is_path_control_active(instance):
     e = _libgs.gsapi_is_path_control_active(instance)
-    return e
+    if e < 0:
+        raise GSError(e)
 
 
 
 # Implementation details.
 #
 
+_Error_num_to_error = dict()
+class _Error:
+    def __init__(self, num, desc):
+        self.num = num
+        self.desc = desc
+        _Error_num_to_error[self.num] = self
+
+gs_error_ok                 = _Error(   0, 'ok')
+gs_error_unknownerror       = _Error(  -1, 'unknown error')
+gs_error_dictfull           = _Error(  -2, 'dict full')
+gs_error_dictstackoverflow  = _Error(  -3, 'dict stack overflow')
+gs_error_dictstackunderflow = _Error(  -4, 'dict stack underflow')
+gs_error_execstackoverflow  = _Error(  -5, 'exec stack overflow')
+gs_error_interrupt          = _Error(  -6, 'interrupt')
+gs_error_invalidaccess      = _Error(  -7, 'invalid access')
+gs_error_invalidexit        = _Error(  -8, 'invalid exit')
+gs_error_invalidfileaccess  = _Error(  -9, 'invalid fileaccess')
+gs_error_invalidfont        = _Error( -10, 'invalid font')
+gs_error_invalidrestore     = _Error( -11, 'invalid restore')
+gs_error_ioerror            = _Error( -12, 'ioerror')
+gs_error_limitcheck         = _Error( -13, 'limit check')
+gs_error_nocurrentpoint     = _Error( -14, 'no current point')
+gs_error_rangecheck         = _Error( -15, 'range check')
+gs_error_stackoverflow      = _Error( -16, 'stack overflow')
+gs_error_stackunderflow     = _Error( -17, 'stack underflow')
+gs_error_syntaxerror        = _Error( -18, 'syntax error')
+gs_error_timeout            = _Error( -19, 'timeout')
+gs_error_typecheck          = _Error( -20, 'type check')
+gs_error_undefined          = _Error( -21, 'undefined')
+gs_error_undefinedfilename  = _Error( -22, 'undefined filename')
+gs_error_undefinedresult    = _Error( -23, 'undefined result')
+gs_error_unmatchedmark      = _Error( -24, 'unmatched mark')
+gs_error_VMerror            = _Error( -25, 'VMerror')
+
+gs_error_configurationerror = _Error( -26, 'configuration error')
+gs_error_undefinedresource  = _Error( -27, 'undefined resource')
+gs_error_unregistered       = _Error( -28, 'unregistered')
+gs_error_invalidcontext     = _Error( -29, 'invalid context')
+gs_error_invalidid          = _Error( -30, 'invalid id')
+
+gs_error_hit_detected       = _Error( -99, 'hit detected')
+gs_error_Fatal              = _Error(-100, 'Fatal')
+gs_error_Quit               = _Error(-101, 'Quit')
+gs_error_InterpreterExit    = _Error(-102, 'Interpreter Exit')
+gs_error_Remap_Color        = _Error(-103, 'Remap Color')
+gs_error_ExecStackUnderflow = _Error(-104, 'Exec Stack Underflow')
+gs_error_VMreclaim          = _Error(-105, 'VM reclaim')
+gs_error_NeedInput          = _Error(-106, 'Need Input')
+gs_error_NeedFile           = _Error(-107, 'Need File')
+gs_error_Info               = _Error(-110, 'Info')
+gs_error_handled            = _Error(-111, 'handled')
+
+def _gs_error_text(gs_error):
+    '''
+    Returns text description of <gs_error>. See base/gserrors.h.
+    '''
+    e = _Error_num_to_error.get(gs_error)
+    if e:
+        return e.desc
+    return 'no error'
+
 
 # The encoding that we use when passing strings to the underlying gsapi_*() C
 # functions. Changed by gsapi_set_arg_encoding().
@@ -626,47 +729,33 @@ if __name__ == '__main__':
 
     print('libgs: %s' % _libgs)
 
-    e, revision  = gsapi_revision()
-    print('libgs.gsapi_revision => e=%s revision=%s' % (e, revision))
-    assert not e
-
-    e, revision = gsapi_revision()
-    print('gsapi_revision() => e=%s: %s' % (e, revision))
-    assert not e
-
+    revision  = gsapi_revision()
+    print('libgs.gsapi_revision() ok: %s' % revision)
 
-    e, instance = gsapi_new_instance(1)
-    print('gsapi_new_instance => e=%s: %s' % (e, instance))
-    assert not e
+    instance = gsapi_new_instance(1)
+    print('gsapi_new_instance() ok: %s' % instance)
 
-    e = gsapi_set_arg_encoding(instance, GS_ARG_ENCODING_UTF8)
-    print('gsapi_set_arg_encoding => e=%s' % e)
-    assert not e
+    gsapi_set_arg_encoding(instance, GS_ARG_ENCODING_UTF8)
+    print('gsapi_set_arg_encoding() ok.')
 
     def stdout_fn(caller_handle, bytes_):
         sys.stdout.write(bytes_.decode('latin-1'))
-    e = gsapi_set_stdio(instance, None, stdout_fn, None)
-    print('gsapi_set_stdio => e=%s' % e)
-    assert not e
+    gsapi_set_stdio(instance, None, stdout_fn, None)
+    print('gsapi_set_stdio() ok.')
 
     d = display_callback()
-    e = gsapi_set_display_callback(instance, d)
-    print('gsapi_set_display_callback => e=%s' % e)
-    assert not e
+    gsapi_set_display_callback(instance, d)
+    print('gsapi_set_display_callback() ok.')
 
-    e = gsapi_set_default_device_list(instance, 'bmp256 bmp32b bmpgray bmpmono bmpsep1 bmpsep8 ccr cdeskjet cdj1600 cdj500')
-    print('gsapi_set_default_device_list => e=%s' % e)
-    assert not e
+    gsapi_set_default_device_list(instance, 'bmp256 bmp32b bmpgray bmpmono bmpsep1 bmpsep8 ccr cdeskjet cdj1600 cdj500')
+    print('gsapi_set_default_device_list() ok.')
 
-    e, l = gsapi_get_default_device_list(instance)
-    print('gsapi_get_default_device_list => e=%s l=%s' % (e, l))
-    assert not e
+    l = gsapi_get_default_device_list(instance)
+    print('gsapi_get_default_device_list() ok: l=%s' % l)
 
-    e = gsapi_init_with_args(instance, ['gs',])
-    print('gsapi_init_with_args => e=%s' % e)
-    assert not e
+    gsapi_init_with_args(instance, ['gs',])
+    print('gsapi_init_with_args() ok')
 
     for value in 32, True, 3.14, 'hello world':
-        e = gsapi_set_param(instance, "foo", value);
-        print('gsapi_set_param %s => e=%s' % (value, e))
-        assert not e
+        gsapi_set_param(instance, "foo", value);
+        print('gsapi_set_param() %s ok.' % value)