py/objexcept: Support errno attribute on OSError exceptions.
This commit adds the errno attribute to exceptions, so code can retrieve errno codes from an OSError using exc.errno. The implementation here simply lets `errno` (and the existing `value`) attributes work on any exception instance (they both alias args[0]). This is for efficiency and to keep code size down. The pros and cons of this are: Pros: - more compatible with CPython, less difference to document and learn - OSError().errno will correctly return None, whereas the current way of doing it via OSError().args[0] will raise an IndexError - it reduces code size on most bare-metal ports (because they already have the errno qstr) - for Python code that uses exc.errno the generated bytecode is 2 bytes smaller and more efficient to execute (compared with exc.args[0]); so bytecode loaded to RAM saves 2 bytes RAM for each use of this attribute, and bytecode that is frozen saves 2 bytes flash/ROM for each use - it's easier/shorter to type, and saves 2 bytes of space in .py files that use it (for each use) Cons: - increases code size by 4-8 bytes on minimal ports that don't already have the `errno` qstr - all exceptions now have .errno and .value attributes (a cpydiff test is added to address this) See also #2407. Signed-off-by: Damien George <damien@micropython.org>
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@ -176,10 +176,6 @@ Exceptions
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.. exception:: OSError
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|see_cpython| `python:OSError`. MicroPython doesn't implement ``errno``
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attribute, instead use the standard way to access exception arguments:
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``exc.args[0]``.
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.. exception:: RuntimeError
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.. exception:: StopIteration
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@ -16,13 +16,13 @@ Constants
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Error codes, based on ANSI C/POSIX standard. All error codes start with
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"E". As mentioned above, inventory of the codes depends on
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:term:`MicroPython port`. Errors are usually accessible as ``exc.args[0]``
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:term:`MicroPython port`. Errors are usually accessible as ``exc.errno``
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where ``exc`` is an instance of `OSError`. Usage example::
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try:
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uos.mkdir("my_dir")
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except OSError as exc:
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if exc.args[0] == uerrno.EEXIST:
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if exc.errno == uerrno.EEXIST:
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print("Directory already exists")
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.. data:: errorcode
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@ -261,7 +261,9 @@ void mp_obj_exception_attr(mp_obj_t self_in, qstr attr, mp_obj_t *dest) {
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if (attr == MP_QSTR_args) {
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decompress_error_text_maybe(self);
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dest[0] = MP_OBJ_FROM_PTR(self->args);
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} else if (self->base.type == &mp_type_StopIteration && attr == MP_QSTR_value) {
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} else if (attr == MP_QSTR_value || attr == MP_QSTR_errno) {
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// These are aliases for args[0]: .value for StopIteration and .errno for OSError.
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// For efficiency let these attributes apply to all exception instances.
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dest[0] = mp_obj_exception_get_value(self_in);
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}
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}
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@ -1,3 +1,5 @@
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# test basic properties of exceptions
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print(repr(IndexError()))
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print(str(IndexError()))
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@ -12,3 +14,6 @@ s = StopIteration()
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print(s.value)
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s = StopIteration(1, 2, 3)
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print(s.value)
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print(OSError().errno)
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print(OSError(1, "msg").errno)
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@ -1,6 +1,10 @@
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# test subclassing a native exception
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class MyExc(Exception):
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pass
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e = MyExc(100, "Some error")
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print(e)
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print(repr(e))
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@ -20,3 +24,19 @@ try:
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raise MyExc("Some error2")
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except:
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print("Caught user exception")
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class MyStopIteration(StopIteration):
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pass
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print(MyStopIteration().value)
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print(MyStopIteration(1).value)
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class MyOSError(OSError):
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pass
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print(MyOSError().errno)
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print(MyOSError(1, "msg").errno)
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9
tests/cpydiff/types_exception_attrs.py
Normal file
9
tests/cpydiff/types_exception_attrs.py
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@ -0,0 +1,9 @@
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"""
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categories: Types,Exception
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description: All exceptions have readable ``value`` and ``errno`` attributes, not just ``StopIteration`` and ``OSError``.
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cause: MicroPython is optimised to reduce code size.
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workaround: Only use ``value`` on ``StopIteration`` exceptions, and ``errno`` on ``OSError`` exceptions. Do not use or rely on these attributes on other exceptions.
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"""
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e = Exception(1)
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print(e.value)
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print(e.errno)
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