Commit Graph

292 Commits

Author SHA1 Message Date
Yonatan Goldschmidt ef9843653b extmod/moducryptolib: Add AES-CTR support.
Selectable at compile time via MICROPY_PY_UCRYPTOLIB_CTR.  Disabled by
default.
2019-05-06 18:09:48 +10:00
Damien George 02cc288edb py: Add independent config for debugging sentinel object values.
The new compile-time option is MICROPY_DEBUG_MP_OBJ_SENTINELS, disabled by
default.  This is to allow finer control of whether this debugging feature
is enabled or not (because, for example, this setting must be the same for
mpy-cross and the MicroPython main code when using native code generation).
2019-03-08 15:53:04 +11:00
Damien George 0779693c23 py/compile: Add optimisation to compile OrderedDict inplace.
This optimisation eliminates the need to create a temporary normal dict.
The optimisation is enabled via MICROPY_COMP_CONST_LITERAL which is enabled
by default (although only has an effect if OrderdDict is enabled).

Thanks to @pfalcon for the initial idea and implementation.
2019-03-01 15:22:46 +11:00
Yonatan Goldschmidt bc4f8b438b extmod/moduwebsocket: Refactor `websocket` to `uwebsocket`.
As mentioned in #4450, `websocket` was experimental with a single intended
user, `webrepl`. Therefore, we'll make this change without a weak
link `websocket` -> `uwebsocket`.
2019-02-14 00:35:45 +11:00
Yonatan Goldschmidt 343401c6df py/mpconfig.h: Fix comments mentioning dangling file and variable names. 2019-02-06 00:25:30 +11:00
Paul Sokolovsky 2f5d113fad py/warning: Support categories for warnings.
Python defines warnings as belonging to categories, where category is a
warning type (descending from exception type). This is useful, as e.g.
allows to disable warnings selectively and provide user-defined warning
types.  So, implement this in MicroPython, except that categories are
represented just with strings.  However, enough hooks are left to implement
categories differently per-port (e.g. as types), without need to patch each
and every usage.
2019-01-31 16:48:30 +11:00
stijn 42863830be py: Add optional support for 2-argument version of built-in next().
Configurable via MICROPY_PY_BUILTINS_NEXT2, disabled by default.
2019-01-27 13:01:28 +11:00
Sean Burton e33bc59712 py: Remove calls to file reader functions when these are disabled.
If MICROPY_PERSISTENT_CODE_LOAD or MICROPY_ENABLE_COMPILER are enabled then
code gets enabled that calls file reading functions which may be disabled
if no readers have been implemented.

To fix this, introduce a MICROPY_HAS_FILE_READER variable, which is
automatically set if MICROPY_READER_POSIX or MICROPY_READER_VFS is set but
can also be manually set if a custom reader is being implemented.  Then
disable the file reading calls if this is not set.
2019-01-27 11:08:25 +11:00
Damien George 3e25d611ef all: Bump version to 1.10. 2019-01-26 00:56:48 +11:00
Damien George aba83e66d7 py/mpconfig.h: Remove parentheses from MICROPY_VERSION_xxx macros.
Otherwise MICROPY_VERSION_STRING includes these parentheses in the string.
2019-01-26 00:44:35 +11:00
Damien George 6d19934463 py: Get optional VM stack overflow check compiling and working again.
Changes to the layout of the bytecode header meant that this debug code was
no longer compiling.  This is now fixed and a new compile-time option is
introduced, MICROPY_DEBUG_VM_STACK_OVERFLOW, to turn on this feature (which
is disabled by default).  This option is needed because more than one file
needs to cooperate to make this check work.
2019-01-04 17:09:41 +11:00
Damien George 7cd59c5bc3 py/mpconfig: Move MICROPY_VERSION macros to static ones in mpconfig.h.
It's more robust to have the version defined statically in a header file,
rather than dynamically generating it via git using a git tag.  In case
git doesn't exist, or a different source control tool is used, it's
important to still have the uPy version number available.
2018-12-22 01:40:38 +11:00
Paul Sokolovsky fbb8335084 py/objdict: Make .fromkeys() method configurable.
On by default, turned off for minimal/bare-arm. Saves 144 bytes on x86.
2018-12-13 01:20:55 +11:00
Paul Sokolovsky 38151f35c1 extmod/moductypes: Add aliases for native C types.
SHORT, INT, LONG, LONGLONG, and unsigned (U*) variants are being defined.
This is done at compile using GCC-style predefined macros like
__SIZEOF_INT__.  If the compiler doesn't have such defines, no such types
will be defined.
2018-12-10 14:40:43 +11:00
Ayke van Laethem 31cf528c75 py: Add option to reduce GC stack integer size to save RAM.
A new option MICROPY_GC_STACK_ENTRY_TYPE is added to select a custom type
instead of size_t for the gc_stack array items.  This can be beneficial for
small devices, especially those that are low on memory anyway.  If a device
has 1MB or less of heap (and 16-byte GC blocks) then this type can be
uint16_t, saving 128 bytes of RAM.
2018-12-04 17:17:25 +11:00
Paul m. p. P 454cca6016 py/objmodule: Implement PEP 562's __getattr__ for modules.
Configurable via MICROPY_MODULE_GETATTR, disabled by default.  Among other
things __getattr__ for modules can help to build lazy loading / code
unloading at runtime.
2018-10-23 11:22:50 +11:00
Paul Sokolovsky 5a91fce9f8 py/objstr: Make str.count() method configurable.
Configurable via MICROPY_PY_BUILTINS_STR_COUNT.  Default is enabled.
Disabled for bare-arm, minimal, unix-minimal and zephyr ports.  Disabling
it saves 408 bytes on x86.
2018-10-22 22:49:05 +11:00
Christopher Swenson 8c656754aa py/modmath: Add math.factorial, optimised and non-opt implementations.
This commit adds the math.factorial function in two variants:
- squared difference, which is faster than the naive version, relatively
  compact, and non-recursive;
- a mildly optimised recursive version, faster than the above one.

There are some more optimisations that could be done, but they tend to take
more code, and more storage space.  The recursive version seems like a
sensible compromise.

The new function is disabled by default, and uses the non-optimised version
by default if it is enabled.  The options are MICROPY_PY_MATH_FACTORIAL
and MICROPY_OPT_MATH_FACTORIAL.
2018-09-26 15:03:04 +10:00
Paul Sokolovsky 2da5d41350 py/objstr: Make % (__mod__) formatting operator configurable.
Default is enabled, disabled for minimal builds. Saves 1296 bytes on x86,
976 bytes on ARM.
2018-09-20 14:41:08 +10:00
Paul Sokolovsky 5fe3730a30 extmod/moduhashlib: Add md5 implementation, using axTLS.
MD5 is still widely used, and may be important in some cases for networking
interoperability, e.g. HTTP Digest authentication.
2018-09-11 14:51:52 +10:00
Damien George da2d2b6d88 py/mpconfig.h: Introduce MICROPY_DEBUG_PRINTER for debugging output.
This patch in effect renames MICROPY_DEBUG_PRINTER_DEST to
MICROPY_DEBUG_PRINTER, moving its default definition from
lib/utils/printf.c to py/mpconfig.h to make it official and documented, and
makes this macro a pointer rather than the actual mp_print_t struct.  This
is done to get consistency with MICROPY_ERROR_PRINTER, and provide this
macro for use outside just lib/utils/printf.c.

Ports are updated to use the new macro name.
2018-08-02 14:04:44 +10:00
Damien George e30a5fc7bc extmod/modure: Add ure.sub() function and method, and tests.
This feature is controlled at compile time by MICROPY_PY_URE_SUB, disabled
by default.

Thanks to @dmazzella for the original patch for this feature; see #3770.
2018-07-02 14:55:02 +10:00
Damien George 1e9b871d29 extmod/modure: Add match.span(), start() and end() methods, and tests.
This feature is controlled at compile time by
MICROPY_PY_URE_MATCH_SPAN_START_END, disabled by default.

Thanks to @dmazzella for the original patch for this feature; see #3770.
2018-07-02 14:54:56 +10:00
Damien George 1f86460910 extmod/modure: Add match.groups() method, and tests.
This feature is controlled at compile time by MICROPY_PY_URE_MATCH_GROUPS,
disabled by default.

Thanks to @dmazzella for the original patch for this feature; see #3770.
2018-07-02 14:53:30 +10:00
Yonatan Goldschmidt 473fe45da2 extmod/moducryptolib: Optionally export MODE_* constants to Python.
Allow including crypto consts based on compilation settings.  Disabled by
default to reduce code size; if one wants extra code readability, can
enable them.
2018-06-27 16:29:26 +10:00
Paul Sokolovsky 567bc2d6ce extmod/moducryptolib: Add ucryptolib module with crypto functions.
The API follows guidelines of https://www.python.org/dev/peps/pep-0272/,
but is optimized for code size, with the idea that full PEP 0272
compatibility can be added with a simple Python wrapper mode.

The naming of the module follows (u)hashlib pattern.

At the bare minimum, this module is expected to provide:

* AES128, ECB (i.e. "null") mode, encrypt only

Implementation in this commit is based on axTLS routines, and implements
following:

* AES 128 and 256
* ECB and CBC modes
* encrypt and decrypt
2018-06-27 14:54:40 +10:00
Yonatan Goldschmidt 6630354ffe extmod/moduhashlib: Allow to disable the sha256 class.
Via the config value MICROPY_PY_UHASHLIB_SHA256.  Default to enabled to
keep backwards compatibility.

Also add default value for the sha1 class, to at least document its
existence.
2018-06-12 13:50:11 +10:00
Damien George af0932a779 py/modio: Add uio.IOBase class to allow to define user streams.
A user class derived from IOBase and implementing readinto/write/ioctl can
now be used anywhere a native stream object is accepted.

The mapping from C to Python is:

    stream_p->read  --> readinto(buf)
    stream_p->write --> write(buf)
    stream_p->ioctl --> ioctl(request, arg)

Among other things it allows the user to:

- create an object which can be passed as the file argument to print:
  print(..., file=myobj), and then print will pass all the data to the
  object via the objects write method (same as CPython)
- pass a user object to uio.BufferedWriter to buffer the writes (same as
  CPython)
- use select.select on a user object
- register user objects with select.poll, in particular so user objects can
  be used with uasyncio
- create user files that can be returned from user filesystems, and import
  can import scripts from these user files

For example:

    class MyOut(io.IOBase):
        def write(self, buf):
            print('write', repr(buf))
            return len(buf)

    print('hello', file=MyOut())

The feature is enabled via MICROPY_PY_IO_IOBASE which is disabled by
default.
2018-06-12 12:29:26 +10:00
Damien George 36c1052183 py/objtype: Optimise instance get/set/del by skipping special accessors.
This patch is a code optimisation, trading text bytes for speed.  On
pyboard it's an increase of 0.06% in code size for a gain (in pystone
performance) of roughly 6.5%.

The patch optimises load/store/delete of attributes in user defined classes
by not looking up special accessors (@property, __get__, __delete__,
__set__, __setattr__ and __getattr_) if they are guaranteed not to exist in
the class.

Currently, if you do my_obj.foo() then the runtime has to do a few checks
to see if foo is a property or has __get__, and if so delegate the call.
And for stores things like my_obj.foo = 1 has to first check if foo is a
property or has __set__ defined on it.

Doing all those checks each and every time the attribute is accessed has a
performance penalty.  This patch eliminates all those checks for cases when
it's guaranteed that the checks will always fail, ie no attributes are
properties nor have any special accessor methods defined on them.

To make this guarantee it checks all attributes of a user-defined class
when it is first created.  If any of the attributes of the user class are
properties or have special accessors, or any of the base classes of the
user class have them, then it sets a flag in the class to indicate that
special accessors must be checked for.  Then in the load/store/delete code
it checks this flag to see if it can take the shortcut and optimise the
lookup.

It's an optimisation that's pretty widely applicable because it improves
lookup performance for all methods of user defined classes, and stores of
attributes, at least for those that don't have special accessors.  And, it
allows to enable descriptors with minimal additional runtime overhead if
they are not used for a particular user class.

There is one restriction on dynamic class creation that has been introduced
by this patch: a user-defined class cannot go from zero special accessors
to one special accessor (or more) after that class has been subclassed.  If
the script attempts this an AttributeError is raised (see addition to
tests/misc/non_compliant.py for an example of this case).

The cost in code space bytes for the optimisation in this patch is:

   unix x64:  +528
unix nanbox:  +508
      stm32:  +192
     cc3200:  +200
    esp8266:  +332
      esp32:  +244

Performance tests that were done:

- on unix x86-64, pystone improved by about 5%
- on pyboard, pystone improved by about 6.5%, from 1683 up to 1794
- on pyboard, bm_chaos (from CPython benchmark suite) improved by about 5%
- on esp32, pystone improved by about 30% (but there are caching effects)
- on esp32, bm_chaos improved by about 11%
2018-06-08 12:12:08 +10:00
Damien George a8b9e71ac1 py/mpconfig.h: Add default MICROPY_VFS_FAT config value.
At least to document it's existence.
2018-06-06 14:33:42 +10:00
Damien George 8d82b0edbd extmod: Add VfsPosix filesystem component.
This VFS component allows to mount a host POSIX filesystem within the uPy
VFS sub-system.  All traditional POSIX file access then goes through the
VFS, allowing to sandbox a uPy process to a certain sub-dir of the host
system, as well as mount other filesystem types alongside the host
filesystem.
2018-06-06 14:28:23 +10:00
Jan Klusacek b318ebf101 py/modbuiltins: Add support for rounding integers.
As per CPython semantics.  This feature is controlled by
MICROPY_PY_BUILTINS_ROUND_INT which is disabled by default.
2018-05-22 14:18:16 +10:00
Damien George 9630376dbc py/mpconfig.h: Be stricter when autodetecting machine endianness.
This patch changes 2 things in the endianness detection:

1. Don't assume that __BYTE_ORDER__ not being __ORDER_LITTLE_ENDIAN__ means
   that the machine is big endian, so add an explicit check that this macro
   is indeed __ORDER_BIG_ENDIAN__ (same with __BYTE_ORDER, __LITTLE_ENDIAN
   and __BIG_ENDIAN).  A machine could have PDP endianness.

2. Remove the checks which base their autodetection decision on whether any
   little or big endian macros are defined (eg __LITTLE_ENDIAN__ or
   __BIG_ENDIAN__).  Just because a system defines these does not mean it
   has that endianness.

See issue #3760.
2018-05-11 21:51:34 +10:00
Paul Sokolovsky 970eedce8f py/objdeque: Implement ucollections.deque type with fixed size.
So far, implements just append() and popleft() methods, required for
a normal queue. Constructor doesn't accept an arbitarry sequence to
initialize from (am empty deque is always created), so an empty tuple
must be passed as such. Only fixed-size deques are supported, so 2nd
argument (size) is required.

There's also an extension to CPython - if True is passed as 3rd argument,
append(), instead of silently overwriting the oldest item on queue
overflow, will throw IndexError. This behavior is desired in many
cases, where queues should store information reliably, instead of
silently losing some items.
2018-02-21 22:39:25 +11:00
Damien George 7e2a48858c py/modmicropython: Allow to have stack_use() func without mem_info().
The micropython.stack_use() function is useful to query the current C stack
usage, and it's inclusion in the micropython module doesn't need to be tied
to the inclusion of mem_info()/qstr_info() because it doesn't rely on any
of the code from these functions.  So this patch introduces the config
option MICROPY_PY_MICROPYTHON_STACK_USE which can be used to independently
control the inclusion of stack_use().  By default it is enabled if
MICROPY_PY_MICROPYTHON_MEM_INFO is enabled (thus not changing any of the
existing ports).
2018-02-20 18:30:22 +11:00
Damien George 209936880d py/builtinimport: Add compile-time option to disable external imports.
The new option is MICROPY_ENABLE_EXTERNAL_IMPORT and is enabled by default
so that the default behaviour is the same as before.  With it disabled
import is only supported for built-in modules, not for external files nor
frozen modules.  This allows to support targets that have no filesystem of
any kind and that only have access to pre-supplied built-in modules
implemented natively.
2018-02-20 18:00:44 +11:00
Damien George d77da83d55 py/objrange: Implement (in)equality comparison between range objects.
This feature is not often used so is guarded by the config option
MICROPY_PY_BUILTINS_RANGE_BINOP which is disabled by default.  With this
option disabled MicroPython will always return false when comparing two
range objects for equality (unless they are exactly the same object
instance).  This does not match CPython so if (in)equality between range
objects is needed then this option should be enabled.

Enabling this option costs between 100 and 200 bytes of code space
depending on the machine architecture.
2018-02-14 23:17:06 +11:00
Damien George 253f2bd7be py/compile: Combine compiler-opt of 2 and 3 tuple-to-tuple assignment.
This patch combines the compiler optimisation code for double and triple
tuple-to-tuple assignment, taking it from two separate if-blocks to one
combined if-block.  This can be done because the code for both of these
optimisations has a lot in common.  Combining them together reduces code
size for ports that have the triple-tuple optimisation enabled (and doesn't
change code size for ports that have it disabled).
2018-02-04 13:35:21 +11:00
Paul Sokolovsky 6364401666 py/objgenerator: Allow to pend an exception for next execution.
This implements .pend_throw(exc) method, which sets up an exception to be
triggered on the next call to generator's .__next__() or .send() method.
This is unlike .throw(), which immediately starts to execute the generator
to process the exception. This effectively adds Future-like capabilities
to generator protocol (exception will be raised in the future).

The need for such a method arised to implement uasyncio wait_for() function
efficiently (its behavior is clearly "Future" like, and normally would
require to introduce an expensive Future wrapper around all native
couroutines, like upstream asyncio does).

py/objgenerator: pend_throw: Return previous pended value.

This effectively allows to store an additional value (not necessary an
exception) in a coroutine while it's not being executed. uasyncio has
exactly this usecase: to mark a coro waiting in I/O queue (and thus
not executed in the normal scheduling queue), for the purpose of
implementing wait_for() function (cancellation of such waiting coro
by a timeout).
2017-12-15 20:20:36 +02:00
Damien George 2759bec858 py: Extend nan-boxing config to have 47-bit small integers.
The nan-boxing representation has an extra 16-bits of space to store
small-int values, and making use of it allows to create and manipulate full
32-bit positive integers (ie up to 0xffffffff) without using the heap.
2017-12-11 22:39:12 +11:00
Damien George 02d830c035 py: Introduce a Python stack for scoped allocation.
This patch introduces the MICROPY_ENABLE_PYSTACK option (disabled by
default) which enables a "Python stack" that allows to allocate and free
memory in a scoped, or Last-In-First-Out (LIFO) way, similar to alloca().

A new memory allocation API is introduced along with this Py-stack.  It
includes both "local" and "nonlocal" LIFO allocation.  Local allocation is
intended to be equivalent to using alloca(), whereby the same function must
free the memory.  Nonlocal allocation is where another function may free
the memory, so long as it's still LIFO.

Follow-up patches will convert all uses of alloca() and VLA to the new
scoped allocation API.  The old behaviour (using alloca()) will still be
available, but when MICROPY_ENABLE_PYSTACK is enabled then alloca() is no
longer required or used.

The benefits of enabling this option are (or will be once subsequent
patches are made to convert alloca()/VLA):
- Toolchains without alloca() can use this feature to obtain correct and
  efficient scoped memory allocation (compared to using the heap instead
  of alloca(), which is slower).
- Even if alloca() is available, enabling the Py-stack gives slightly more
  efficient use of stack space when calling nested Python functions, due to
  the way that compilers implement alloca().
- Enabling the Py-stack with the stackless mode allows for even more
  efficient stack usage, as well as retaining high performance (because the
  heap is no longer used to build and destroy stackless code states).
- With Py-stack and stackless enabled, Python-calling-Python is no longer
  recursive in the C mp_execute_bytecode function.

The micropython.pystack_use() function is included to measure usage of the
Python stack.
2017-12-11 13:49:09 +11:00
Paul Sokolovsky e7fc765880 unix/mpconfigport: Disable uio.resource_stream().
This function was implemented as an experiment, and was enabled only in
unix port. To remind, it allows to access arbitrary files frozen as
source modules (vs bytecode).

However, further experimentation showed that the same functionality can
be implemented with frozen bytecode. The process requires more steps, but
with suitable toolset it doesn't matter patch. This process is:

1. Convert binary files into "Python resource module" with
tools/mpy_bin2res.py.
2. Freeze as the bytecode.
3. Use micropython-lib's pkg_resources.resource_stream() to access it.

In other words, the extra step is using tools/mpy_bin2res.py (because
there would be wrapper for uio.resource_stream() anyway).

Going frozen bytecode route allows more flexibility, and same/additional
efficiency:

1. Frozen source support can be disabled altogether for additional code
savings.
2. Resources could be also accessed as a buffer, not just as a stream.

There're few caveats too:

1. It wasn't actually profiled the overhead of storing a resource in
"Python resource module" vs storing it directly, but it's assumed that
overhead is small.
2. The "efficiency" claim above applies to the case when resource
file is frozen as the bytecode. If it's not, it actually will take a
lot of RAM on loading. But in this case, the resource file should not
be used (i.e. generated) in the first place, and micropython-lib's
pkg_resources.resource_stream() implementation has the appropriate
fallback to read the raw files instead. This still poses some distribution
issues, e.g. to deployable to baremetal ports (which almost certainly
would require freezeing as the bytecode), a distribution package should
include the resource module. But for non-freezing deployment, presense
of resource module will lead to memory inefficiency.

All the discussion above reminds why uio.resource_stream() was implemented
in the first place - to address some of the issues above. However, since
then, frozen bytecode approach seems to prevail, so, while there're still
some issues to address with it, this change is being made.

This change saves 488 bytes for the unix x86_64 port.
2017-12-10 02:38:23 +02:00
Damien George da154fdaf9 py: Add config option to disable multiple inheritance.
This patch introduces a new compile-time config option to disable multiple
inheritance at the Python level: MICROPY_MULTIPLE_INHERITANCE.  It is
enabled by default.

Disabling multiple inheritance eliminates a lot of recursion in the call
graph (which is important for some embedded systems), and can be used to
reduce code size for ports that are really constrained (by around 200 bytes
for Thumb2 archs).

With multiple inheritance disabled all tests in the test-suite pass except
those that explicitly test for multiple inheritance.
2017-11-20 16:18:50 +11:00
stijn 79ed58f87b py/objnamedtuple: Add _asdict function if OrderedDict is supported 2017-11-12 14:16:54 +02:00
Paul Sokolovsky 1b146e9de9 py/mpconfig: Introduce reusable MP_HTOBE32(), etc. macros.
Macros to convert big-endian values to host byte order and vice-versa.
These were defined in adhoc way for some ports (e.g. esp8266), allow
reuse, provide default implementations, while allow ports to override.
2017-11-08 19:47:37 +02:00
Eric Poulsen 74ec52d857 extmod/modussl: Add finaliser support for ussl objects.
Per the comment found here
https://github.com/micropython/micropython-esp32/issues/209#issuecomment-339855157,
this patch adds finaliser code to prevent memory leaks from ussl objects,
which is especially useful when memory for a ussl context is allocated
outside the uPy heap.  This patch is in-line with the finaliser code found
in many modsocket implementations for various ports.

This feature is configured via MICROPY_PY_USSL_FINALISER and is disabled by
default because there may be issues using it when the ussl state *is*
allocated on the uPy heap, rather than externally.
2017-10-30 15:25:32 +11:00
Paul Sokolovsky 0e80f345f8 py/objtype: Introduce MICROPY_PY_ALL_INPLACE_SPECIAL_METHODS.
This allows to configure support for inplace special methods separately,
similar to "normal" and reverse special methods. This is useful, because
inplace methods are "the most optional" ones, for example, if inplace
methods aren't defined, the operation will be executed using normal
methods instead.

As a caveat, __iadd__ and __isub__ are implemented even if
MICROPY_PY_ALL_INPLACE_SPECIAL_METHODS isn't defined. This is similar
to the state of affairs before binary operations refactor, and allows
to run existing tests even if MICROPY_PY_ALL_INPLACE_SPECIAL_METHODS
isn't defined.
2017-10-27 22:29:15 +03:00
David Lechner 62849b7010 py: Add config option to print warnings/errors to stderr.
This adds a new configuration option to print runtime warnings and errors to
stderr. On Unix, CPython prints warnings and unhandled exceptions to stderr,
so the unix port here is configured to use this option.

The unix port already printed unhandled exceptions on the main thread to
stderr. This patch fixes unhandled exceptions on other threads and warnings
(issue #2838) not printing on stderr.

Additionally, a couple tests needed to be fixed to handle this new behavior.
This is done by also capturing stderr when running tests.
2017-09-26 11:59:11 +10:00
Damien George 44f0a4d1e7 py/mpconfig.h: Add note that using computed gotos in VM is not C99. 2017-09-18 23:53:33 +10:00
Paul Sokolovsky eb84a830df py/runtime: Implement dispatch for "reverse op" special methods.
If, for class X, X.__add__(Y) doesn't exist (or returns NotImplemented),
try Y.__radd__(X) instead.

This patch could be simpler, but requires undoing operand swap and
operation switch to get non-confusing error message in case __radd__
doesn't exist.
2017-09-10 17:05:57 +03:00