In Python 3.7 the behaviour of repr() of an exception with one argument
changed: it no longer prints a trailing comma in the argument list. See
https://bugs.python.org/issue30399
This patch modifies tests that rely on this behaviour to not rely on it.
And the python34.py test is updated to include a test for this behaviour
with a .exp file.
Input files like basics/string_format.py and float/string_format.py have
the same basename so using that name for writing the output (.exp and .out
files) when both tests fail, results in the output of the first one being
overwritten.
Avoid this by using unique names for the output, replacing path characters
with underscores.
With the recent change b488a4a848, a
generating function now has the same layout in memory as a normal bytecode
function, and so can reuse the latter's attribute accessor code to
implement __name__.
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.
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.
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.
Before this patch the context manager's __aexit__() method would not be
executed if a return/break/continue statement was used to exit an async
with block. async with now has the same semantics as normal with.
The fix here applies purely to the compiler, and does not modify the
runtime at all. It might (eventually) be better to define new bytecode(s)
to handle async with (and maybe other async constructs) in a cleaner, more
efficient way.
One minor drawback with addressing this issue purely in the compiler is
that it wasn't possible to get 100% CPython semantics. The thing that is
different here to CPython is that the __aexit__ method is not looked up in
the context manager until it is needed, which is after the body of the
async with statement has executed. So if a context manager doesn't have
__aexit__ then CPython raises an exception before the async with is
executed, whereas uPy will raise it after it is executed. Note that
__aenter__ is looked up at the beginning in uPy because it needs to be
called straightaway, so if the context manager isn't a context manager then
it'll still raise an exception at the same location as CPython. The only
difference is if the context manager has the __aenter__ method but not the
__aexit__ method, then in that case uPy has different behaviour. But this
is a very minor, and acceptable, difference.
This behaviour of a NULL write C method on a stream that uses the write
adaptor objects is no longer supported. It was only ever used by the
coverage build for testing the fail path of mp_get_stream_raise().
For i2c.py: the accelerometer now uses the new I2C driver so need to
explicitly init the legacy i2c object to get the test working.
For pyb1.py: the legacy pyb.hid() call will crash if the USB_HID object is
not initialised.
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%
This conditional import was only used to get the tests working on the unix
coverage build, which has now switched to use VFS by default so the uos
module alone has the required functionality.
Printing of uPy floats can differ by the floating-point precision on
different architectures (eg 64-bit vs 32-bit x86), so it's not possible to
using printing of floats in some parts of this test. Instead we can just
check for equivalence with what is known to be the correct answer.
Commit e269cabe3e added a check that the
first argument to the to_bytes() method is an integer, and now uPy
follows CPython behaviour and raises a TypeError for this test.
Note: CPython checks the argument types before checking the number of
arguments, but uPy does it the other way around, so they give different
exception messages for this test, but still the same type, a TypeError.
In adcall.py the pyb module may not be imported, so use ADCAll directly.
In dac.py the DAC object now prints more info, so update .exp file.
In spi.py the SPI should be deinitialised upon exit, so the test can run a
second time correctly.
If MICROPY_USE_INTERNAL_ERRNO is disabled, MP_EINVAL is not guaranteed
to have the value 22, so we cannot depend on OSError(22,).
Instead, to support any given port's errno values, without relying
on uerrno, we just check that the args[0] is positive.
This can be used to select the output buffer behaviour of the DAC. The
default values are chosen to retain backwards compatibility with existing
behaviour.
Thanks to @peterhinch for the initial idea to add this feature.
Reading into a bytearray will truncate values to 0xff so the assertions
checking read_timed() would previously always succeed.
Thanks to @peterhinch for finding this problem and providing the solution.
Keeping all the stress related tests in one place makes it easier to
stress-test a given port, and to also not run such tests on ports that
can't handle them.
The string "Q+?" is special in that it hashes to zero with the djb2
algorithm (among other strings), and a zero hash should be incremented to a
hash of 1.
The case of a return statement in the try suite of a try-except statement
was previously only tested by builtin_compile.py, and only then in the part
of this test which checked for the existence of the compile builtin. So
this patch adds an explicit unit test for this case.
The VM expects that, if mp_resume() returns MP_VM_RETURN_EXCEPTION, then
the returned value is an exception instance (eg to add a traceback to it).
It's possible that a value passed to a generator's throw() is not an
exception so must be explicitly checked for if the thrown value is not
intercepted by the generator.
Thanks to @jepler for finding the bug.
Prior to this patch the code would crash if a key in a ** dict was anything
other than a str or qstr. This is because mp_setup_code_state() assumes
that keys in kwargs are qstrs (for efficiency).
Thanks to @jepler for finding the bug.
This is just to test that the function exists and returns some kind of
valid value. Although this file is for testing ms/us functions, put the
ticks_cpu() test here so not to add a new test file.
This test for calling gc_realloc() while the GC is locked can be done in
pure Python, so better to do it that way since it can then be tested on
more ports.
Prior to this patch, some architectures (eg unix x86) could render floats
with "negative" digits, like ")". For example, '%.23e' % 1e-80 would come
out as "1.0000000000000000/)/(,*0e-80". This patch fixes the known cases.
Prior to this patch, some architectures (eg unix x86) could render floats
with a ":" character in them, eg 1e+39 would come out as ":e+38" (":" is
just after "9" in ASCII so this is like 10e+38). This patch fixes some of
these cases.
Prior to this patch the %f formatting of some FP values could be off by up
to 1, eg '%.0f' % 123 would return "122" (unix x64). Depending on the FP
precision (single vs double) certain numbers would format correctly, but
others wolud not. This patch should fix all cases of rounding for %f.
This patch concerns the handling of an NLR-raised StopIteration, raised
during a call to mp_resume() which is handling the yield from opcode.
Previously, commit 6738c1dded introduced code
to handle this case, along with a test. It seems that it was lucky that
the test worked because the code did not correctly handle the stack pointer
(sp).
Furthermore, commit 79d996a57b improved the
way mp_resume() propagated certain exceptions: it changed raising an NLR
value to returning MP_VM_RETURN_EXCEPTION. This change meant that the
test introduced in gen_yield_from_ducktype.py was no longer hitting the
code introduced in 6738c1dded.
The patch here does two things:
1. Fixes the handling of sp in the VM for the case that yield from is
interrupted by a StopIteration raised via NLR.
2. Introduces a new test to check this handling of sp and re-covers the
code in the VM.
Float parsing (both single and double precision) may have a relative error
of order the floating point precision, so adjust tests to take this into
account by not printing all of the digits of the answer.
These new tests cover cases that can't be reached from Python and get
coverage of py/mpz.c to 100%.
These "unreachable from Python" pieces of code could be removed but they
form an integral part of the mpz C API and may be useful for non-Python
usage of mpz.
There is a finite list of ascending primes used for the size of a hash
table, and this test tests that the code can handle a dict larger than the
maximum value in that list of primes. Adding this tests gets py/map.c to
100% coverage.
Otherwise passing -1 as maxlen will lead to a zero allocation and
subsequent unbound buffer overflow in deque.append() because i_put is
allowed to grow without bound.
Prior to this patch uPy (on a 32-bit arch) would have severe issues when
calling bytes(-1): such a call would call vstr_init_len(vstr, -1) which
would then +1 on the len and call vstr_init(vstr, 0), which would then
round this up and allocate a small amount of memory for the vstr. The
bytes constructor would then attempt to zero out all this memory, thinking
it had allocated 2^32-1 bytes.
This patch changes the way REPL autocomplete finds matches. It now probes
the target object for all qstrs via mp_load_method_maybe to look for a
match with the given input string. Similar to how the builtin dir()
function works, this new algorithm now find all methods and instances of
user-defined classes including attributes of their parent classes. This
helps a lot at the REPL prompt for user-discovery and to autocomplete names
even for classes that are derived.
The downside is that this new algorithm is slower than the previous one,
and in particular will be slower the more qstrs there are in the system.
But because REPL autocomplete is primarily used in an interactive way it is
not that important to make it fast, as long as it is "fast enough" compared
to human reaction.
On a slow microcontroller (CPU running at 16MHz) the autocomplete time for
a list of 35 names in the outer namespace (pressing tab at a bare prompt)
takes about 160ms with this algorithm, compared to about 40ms for the
previous implementation (this time includes the actual printing of the
names as well). This time of 160ms is very reasonable especially given the
new functionality of listing all the names.
This patch also decreases code size by:
bare-arm: +0
minimal x86: -128
unix x64: -128
unix nanbox: -224
stm32: -88
cc3200: -80
esp8266: -92
esp32: -84
This patch improves the builtin dir() function by probing the target object
with all possible qstrs via mp_load_method_maybe. This is very simple (in
terms of implementation), doesn't require recursion, and allows to list all
methods of user-defined classes (without duplicates) even if they have
multiple inheritance with a common parent. The downside is that it can be
slow because it has to iterate through all the qstrs in the system, but
the "dir()" function is anyway mostly used for testing frameworks and user
introspection of types, so speed is not considered a priority.
In addition to providing a more complete implementation of dir(), this
patch is simpler than the previous implementation and saves some code
space:
bare-arm: -80
minimal x86: -80
unix x64: -56
unix nanbox: -48
stm32: -80
cc3200: -80
esp8266: -104
esp32: -64
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.
Instead of putting just 'CRASH' in the .py.out file, this patch makes it so
any output from uPy that led to the crash is stored in the .py.out file, as
well as the 'CRASH' message at the end.
Prior to this patch, a float literal that was close to subnormal would
have a loss of precision when parsed. The worst case was something like
float('10000000000000000000e-326') which returned 0.0.
Note that the check for elem!=NULL is removed for the
MP_MAP_LOOKUP_ADD_IF_NOT_FOUND case because mp_map_lookup will always
return non-NULL for such a case.
CPython doesn't allow SEEK_CUR with non-zero offset for files in text mode,
and uPy inherited this behaviour for both text and binary files. It makes
sense to provide full support for SEEK_CUR of binary-mode files in uPy, and
to do this in a minimal way means also allowing to use SEEK_CUR with
non-zero offsets on text-mode files. That seems to be a fair compromise.
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).
The whole idea of --list-tests is that we prepare a list of tests to run
later, and currently don't have a connection to target board. Similarly
for --write-exp - only "python3" binary would be required for this operation,
not "micropython".
The idea that --list-tests would be enough to produce list of tests for
tinytest-codegen didn't work, because normal run-tests processing heavily
relies on dynamic target capabilities discovery, and test filtering happens
as the result of that.
So, approach the issue from different end - allow to specify arbitrary
filtering criteria as run-tests arguments. This way, specific filters
will be still hardcoded, but at least on a particular target's side,
instead of constant patching tinytest-codegen and/or run-tests.
Lists tests to be executed, subject to all other filters requested. This
options would be useful e.g. for scripts like tools/tinytest-codegen.py,
which currently contains hardcoded filters for particular a particular
target and can't work for multiple targets.
"Builtin" tinytest-based testsuite as employed by qemu-arm (and now
generalized by me to be reusable for other targets) performs simplified
detection of skipped tests, it treats as such tests which raised SystemExit
(instead of checking got "SKIP" output). Consequently, each "SKIP" must
be accompanied by SystemExit (and conversely, SystemExit should not be
used if test is not skipped, which so far seems to be true).
These tests involves testing allocation-free function calling, and in strict
stackless mode, it's not possible to make a function call with heap locked
(because function activation record aka frame is allocated on the heap).
In strict stackless mode, it's not possible to make a function call with
heap locked (because function activation record aka frame is allocated on
heap). So, if the only purpose of function is to introduce local variable
scope, move heap lock/unlock calls inside the function.
This patch improves parsing of floating point numbers by converting all the
digits (integer and fractional) together into a number 1 or greater, and
then applying the correct power of 10 at the very end. In particular the
multiple "multiply by 0.1" operations to build a fraction are now combined
together and applied at the same time as the exponent, at the very end.
This helps to retain precision during parsing of floats, and also includes
a check that the number doesn't overflow during the parsing. One benefit
is that a float will have the same value no matter where the decimal point
is located, eg 1.23 == 123e-2.
Before this patch MP_BINARY_OP_IN had two meanings: coming from bytecode it
meant that the args needed to be swapped, but coming from within the
runtime meant that the args were already in the correct order. This lead
to some confusion in the code and comments stating how args were reversed.
It also lead to 2 bugs: 1) containment for a subclass of a native type
didn't work; 2) the expression "{True} in True" would illegally succeed and
return True. In both of these cases it was because the args to
MP_BINARY_OP_IN ended up being reversed twice.
To fix these things this patch introduces MP_BINARY_OP_CONTAINS which
corresponds exactly to the __contains__ special method, and this is the
operator that built-in types should implement. MP_BINARY_OP_IN is now only
emitted by the compiler and is converted to MP_BINARY_OP_CONTAINS by
swapping the arguments.
If MICROPY_PY_ALL_SPECIAL_METHODS is defined, actually define all special
methods (still subject to gating by e.g. MICROPY_PY_REVERSE_SPECIAL_METHODS).
This adds quite a number of qstr's, so should be used sparingly.
CPython only supports the server_hostname keyword arg via the SSLContext
object, so use that instead of the top-level ssl.wrap_socket. This allows
the test to run on CPython the same as uPy.
Also add the "Host:" header to correctly make a GET request (for URLs that
are hosted on other servers). This is not strictly needed to test the SSL
connection but helps to debug things when printing the response.
This patch changes how most of the plain math functions are implemented:
there are now two generic math wrapper functions that take a pointer to a
math function (like sin, cos) and perform the necessary conversion to and
from MicroPython types. This helps to reduce code size. The generic
functions can also check for math domain errors in a generic way, by
testing if the result is NaN or infinity combined with finite inputs.
The result is that, with this patch, all math functions now have full
domain error checking (even gamma and lgamma) and code size has decreased
for most ports. Code size changes in bytes for those with the math module
are:
unix x64: -432
unix nanbox: -792
stm32: -88
esp8266: +12
Tests are also added to check domain errors are handled correctly.
We want to close communication object even if there were exceptions
somewhere in the code. This is important for --device exec:/execpty:
which may otherwise leave processing running in the background.
CPython docs explicitly state that the RHS of a set/frozenset binary op
must be a set to prevent user errors. It also preserves commutativity of
the ops, eg: "abc" & set() is a TypeError, and so should be set() & "abc".
This change actually decreases unix (x64) code by 160 bytes; it increases
stm32 by 4 bytes and esp8266 by 28 bytes (but previous patch already
introduced a much large saving).
This returns a complex number, following CPython behaviour. For ports that
don't have complex numbers enabled this will raise a ValueError which gives
a fail-safe for scripts that were written assuming complex numbers exist.
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.
Current users of fixed vstr buffers (building file paths) assume that there
is no overflow and do not check for overflow after building the vstr. This
has the potential to lead to NULL pointer dereferences
(when vstr_null_terminated_str returns NULL because it can't allocate RAM
for the terminating byte) and stat'ing and loading invalid path names (due
to the path being truncated). The safest and simplest thing to do in these
cases is just raise an exception if a write goes beyond the end of a fixed
vstr buffer, which is what this patch does. It also simplifies the vstr
code.
The aim of this patch is to rewrite the functions that create exception
instances (mp_obj_exception_make_new and mp_obj_new_exception_msg_varg) so
that they do not call any functions that may raise an exception. Otherwise
it's possible to create infinite recursion with an exception being raised
while trying to create an exception object.
The two main things that are done to accomplish this are:
1. Change mp_obj_new_exception_msg_varg to just format the string, then
call mp_obj_exception_make_new to actually create the exception object.
2. In mp_obj_exception_make_new and mp_obj_new_exception_msg_varg try to
allocate all memory first using functions that don't raise exceptions
If any of the memory allocations fail (return NULL) then degrade
gracefully by trying other options for memory allocation, eg using the
emergency exception buffer.
3. Use a custom printer backend to conservatively format strings: if it
can't allocate memory then it just truncates the string.
As part of this rewrite, raising an exception without a message, like
KeyError(123), will now use the emergency buffer to store the arg and
traceback data if there is no heap memory available.
Memory use with this patch is unchanged. Code size is increased by:
bare-arm: +136
minimal x86: +124
unix x64: +72
unix nanbox: +96
stm32: +88
esp8266: +92
cc3200: +80
This allows user classes to implement __abs__ special method, and saves
code size (104 bytes for x86_64), even though during refactor, an issue
was fixed and few optimizations were made:
* abs() of minimum (negative) small int value is calculated properly.
* objint_longlong and objint_mpz avoid allocating new object is the
argument is already non-negative.
This is to allow to place reverse ops immediately after normal ops, so
they can be tested as one range (which is optimization for reverse ops
introduction in the next patch).
It starts a dichotomy of mp_binary_op_t values which can't appear in the
bytecode. Another reason to move it is to VALUES of OP_* and OP_INPLACE_*
nicely adjacent. This also will be needed for OP_REVERSE_*, to be soon
introduced.
This patch adds a function utf8_check() to check for a valid UTF-8 encoded
string, and calls it when constructing a str from raw bytes. The feature
is selectable at compile time via MICROPY_PY_BUILTINS_STR_UNICODE_CHECK and
is enabled if unicode is enabled. It costs about 110 bytes on Thumb-2, 150
bytes on Xtensa and 170 bytes on x86-64.
IEEE floating point is specified such that a comparison of NaN with itself
returns false, and Python respects these semantics. This patch makes uPy
also have these semantics. The fix has a minor impact on the speed of the
object-equality fast-path, but that seems to be unavoidable and it's much
more important to have correct behaviour (especially in this case where
the wrong answer for nan==nan is silently returned).
These are now returned as "operation not supported" instead of raising
TypeError. In particular, this fixes equality for float vs incompatible
types, which now properly results in False instead of exception. This
also paves the road to support reverse operation (e.g. __radd__) with
float objects.
This is achieved by introducing mp_obj_get_float_maybe(), similar to
existing mp_obj_get_int_maybe().
Prior to this patch, the size of the buffer given to pack_into() was checked
for being too small by using the count of the arguments, not their actual
size. For example, a format spec of '4I' would only check that there was 4
bytes available, not 16; and 'I' would check for 1 byte, not 4.
The pack() function is ok because its buffer is created to be exactly the
correct size.
The fix in this patch calculates the total size of the format spec at the
start of pack_into() and verifies that the buffer is large enough. This
adds some computational overhead, to iterate through the whole format spec.
The alternative is to check during the packing, but that requires extra
code to handle alignment, and the check is anyway not needed for pack().
So to maintain minimal code size the check is done using struct_calcsize.
Prior to this patch, the size of the buffer given to unpack/unpack_from was
checked for being too small by using the count of the arguments, not their
actual size. For example, a format spec of '4I' would only check that
there was 4 bytes available, not 16; and 'I' would check for 1 byte, not 4.
This bug is fixed in this patch by calculating the total size of the format
spec at the start of the unpacking function. This function anyway needs to
calculate the number of items at the start, so calculating the total size
can be done at the same time.
This patch makes a repeat counter behave the same as repeating the
typecode, when there are not enough args. For example:
struct.pack('2I', 1) now behave the same as struct.pack('II', 1).
Similar to the existing testcase, but test that returning both value of
native type and instance of another user class from __new__ lead to
__init__ not being called, for better coverage.
NotImplemented means "try other fallbacks (like calling __rop__
instead of __op__) and if nothing works, raise TypeError". As
MicroPython doesn't implement any fallbacks, signal to raise
TypeError right away.
Otherwise, it will silently get incorrect result on other values types,
including CPython tuple form like "foo.png".endswith(("png", "jpg"))
(which MicroPython doesn't support for unbloatedness).
This implementation ignores invalid characters in the input. This allows
it to decode the output of b2a_base64, and also mimics the behavior of
CPython.
The value of 0 can't be used because otherwise mp_binary_get_size will let
a null byte through as the type code (intepreted as byterray). This can
lead to invalid type-specifier strings being let through without an error
in the struct module, and even buffer overruns.
The idea is that these tests can be run with just a test server running
on a test host, with device under test connecting to it, instead of
requiring Internet connection for testing.
Such setup is however WIP, and some tests in net_hosted/ are so far
written to connect to Internet, as there're not test server written
yet. This is expected to evolve over time.
This attempts to bootstrap network tests for MicroPython. This commits
sets test/net_inet/ as place for tests which require access to wide
Internet. They aren't intended to be run as part of the main testsuite,
instead to be run manually on demand.
test_tls_sites.py in particular check that it's possible to establish
SSL/TLS connection to select sites on the Internet: few references ones,
plus those for which problems were reported, and resolved.
In CPython 3.4 this raises a SyntaxError. In CPython 3.5+ having a
positional after * is allowed but uPy has the wrong semantics and passes
the arguments in the incorrect order. To prevent incorrect use of a
function going unnoticed it is important to raise the SyntaxError in uPy,
until the behaviour is fixed to follow CPython 3.5+.
This patch fixes 2 things when printing a floating-point number that
requires rounding up of the mantissa:
- retain the correct precision; eg 0.99 becomes 1.0, not 1.00
- if the exponent goes from -1 to 0 then render it as +0, not -0
Tests for an issue with line continuation failing in paste mode due to the
lexer only checking for \n in the "following" character position, before
next_char() has had a chance to convert \r and \r\n to \n.
