Optimize memoryview comparison: a memoryview is equal to itself, there is no
need to compare values, except if it uses float format.
Benchmark comparing 1 MiB:
from timeit import timeit
with open("/dev/random", 'br') as fp:
data = fp.read(2**20)
view = memoryview(data)
LOOPS = 1_000
b = timeit('x == x', number=LOOPS, globals={'x': data})
m = timeit('x == x', number=LOOPS, globals={'x': view})
print("bytes %f seconds" % b)
print("mview %f seconds" % m)
print("=> %f time slower" % (m / b))
Result before the change:
bytes 0.000026 seconds
mview 1.445791 seconds
=> 55660.873940 time slower
Result after the change:
bytes 0.000026 seconds
mview 0.000028 seconds
=> 1.104382 time slower
This missed optimization was discovered by Pierre-Yves David
while working on Mercurial.
Co-authored-by: Pieter Eendebak <pieter.eendebak@gmail.com>
subclasses of list or dict and haven't implemented any pickle-related
methods (__reduce__, __reduce_ex__, __getnewargs__, __getnewargs_ex__,
or __getstate__), can no longer be pickled. Including memoryview.
I have compared output between pre- and post-patch runs of these tests
to make sure there's nothing missing and nothing broken, on both
Windows and Linux. The only differences I found were actually tests
that were previously *not* run.
and lifetime issues of dynamically allocated Py_buffer members (#9990)
as well as crashes (#8305, #7433). Many new features have been added
(See whatsnew/3.3), and the documentation has been updated extensively.
The ndarray test object from _testbuffer.c implements all aspects of
PEP-3118, so further development towards the complete implementation
of the PEP can proceed in a test-driven manner.
Thanks to Nick Coghlan, Antoine Pitrou and Pauli Virtanen for review
and many ideas.
- Issue #12834: Fix incorrect results of memoryview.tobytes() for
non-contiguous arrays.
- Issue #5231: Introduce memoryview.cast() method that allows changing
format and shape without making a copy of the underlying memory.
frombytes() and tobytes(), respectively, to avoid confusion. Furthermore,
array.frombytes(), array.extend() as well as the array.array()
constructor now accept bytearray objects. Patch by Thomas Jollans.
Also fix len() to return number of items rather than length in bytes.
I'm sorry it was not possible for me to work on this without reindenting
a bit some stuff around. The indentation in memoryobject.c is a mess,
I'll open a separate bug for it.
