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comparison Python/errors.c @ 6:fc6fcd7df4f7 legacy-trunk

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Initial revision
author Guido van Rossum <guido@python.org>
date Sun, 14 Oct 1990 12:07:46 +0000
parents
children 33701db4ea55
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5:5570dbb1ce55 6:fc6fcd7df4f7
1 /* Error handling -- see also run.c */
2
3 /* New error handling interface.
4
5 The following problem exists (existed): methods of built-in modules
6 are called with 'self' and 'args' arguments, but without a context
7 argument, so they have no way to raise a specific exception.
8 The same is true for the object implementations: no context argument.
9 The old convention was to set 'errno' and to return NULL.
10 The caller (usually call_function() in eval.c) detects the NULL
11 return value and then calls puterrno(ctx) to turn the errno value
12 into a true exception. Problems with this approach are:
13 - it used standard errno values to indicate Python-specific errors,
14 but this means that when such an error code is reported by UNIX the
15 user gets a confusing message
16 - errno is a global variable, which makes extensions to a multi-
17 threading environment difficult; e.g., in IRIX, multi-threaded
18 programs must use the function getoserror() (sp.?) instead of
19 looking in errno
20 - there is no portable way to add new error numbers for specic
21 situations -- the value space for errno is reserved to the OS, yet
22 the way to turn module-specific errors into a module-specific
23 exception requires module-specific values for errno
24 - there is no way to add a more situation-specific message to an
25 error.
26
27 The new interface solves all these problems. To return an error, a
28 built-in function calls err_set(exception), err_set(valexception,
29 value) or err_setstr(exception, string), and returns NULL. These
30 functions save the value for later use by puterrno(). To adapt this
31 scheme to a multi-threaded environment, only the implementation of
32 err_setval() has to be changed.
33 */
34
35 #include <stdio.h>
36
37 #include "PROTO.h"
38 #include "object.h"
39 #include "stringobject.h"
40 #include "errors.h"
41
42 /* Last exception stored by err_setval() */
43
44 static object *last_exception;
45 static object *last_exc_val;
46
47 void
48 err_setval(exception, value)
49 object *exception;
50 object *value;
51 {
52 if (last_exception != NULL)
53 DECREF(last_exception);
54 if (exception != NULL)
55 INCREF(exception);
56 last_exception = exception;
57
58 if (last_exc_val != NULL)
59 DECREF(last_exc_val);
60 if (value != NULL)
61 INCREF(value);
62 last_exc_val = value;
63 }
64
65 void
66 err_set(exception)
67 object *exception;
68 {
69 err_setval(exception, (object *)NULL);
70 }
71
72 void
73 err_setstr(exception, string)
74 object *exception;
75 char *string;
76 {
77 object *value = newstringobject(string);
78 err_setval(exception, value);
79 if (value != NULL)
80 DECREF(value);
81 }
82
83 int
84 err_occurred()
85 {
86 return last_exception != NULL;
87 }
88
89 void
90 err_get(p_exc, p_val)
91 object **p_exc;
92 object **p_val;
93 {
94 *p_exc = last_exception;
95 last_exception = NULL;
96 *p_val = last_exc_val;
97 last_exc_val = NULL;
98 }
99
100 void
101 err_clear()
102 {
103 if (last_exception != NULL) {
104 DECREF(last_exception);
105 last_exception = NULL;
106 }
107 if (last_exc_val != NULL) {
108 DECREF(last_exc_val);
109 last_exc_val = NULL;
110 }
111 }