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Re: [Qemu-devel] [RFC PATCH] remove numpy dependency
From: |
Stefan Hajnoczi |
Subject: |
Re: [Qemu-devel] [RFC PATCH] remove numpy dependency |
Date: |
Tue, 7 Nov 2017 10:52:44 +0000 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
On Mon, Nov 06, 2017 at 07:35:55PM +0300, Joannah Nanjekye wrote:
> Users tend to hit an ImportError when running analyze-migration.py due
> to the numpy dependency. numpy functionality isn't actually used, just
> binary serialization that the standard library 'struct' module already
> provides. Removing the dependency allows the script to run
> out-of-the-box.
>
> Signed-off-by: Joannah Nanjekye <address@hidden>
> ---
> scripts/analyze-migration.py | 23 +++++++++++++++--------
> 1 file changed, 15 insertions(+), 8 deletions(-)
>
> diff --git a/scripts/analyze-migration.py b/scripts/analyze-migration.py
> index 1455387..6175c99 100755
> --- a/scripts/analyze-migration.py
> +++ b/scripts/analyze-migration.py
> @@ -17,7 +17,6 @@
> # You should have received a copy of the GNU Lesser General Public
> # License along with this library; if not, see
> <http://www.gnu.org/licenses/>.
>
> -import numpy as np
> import json
> import os
> import argparse
> @@ -36,23 +35,29 @@ class MigrationFile(object):
> self.file = open(self.filename, "rb")
>
> def read64(self):
> - return np.asscalar(np.fromfile(self.file, count=1, dtype='>i8')[0])
dtype='>i8' is a 64-bit (8 bytes) big-endian signed integer according to
https://docs.scipy.org/doc/numpy-1.13.0/reference/arrays.dtypes.html#arrays-dtypes-constructing.
> + buffer = file.read(64)
This reads 64 bytes (not bits!). It should read 8 bytes.
> + return struct.unpack('>i16', buffer)[0]
This should be '>q' according to
https://docs.python.org/2.7/library/struct.html#format-strings.
>
> def read32(self):
> - return np.asscalar(np.fromfile(self.file, count=1, dtype='>i4')[0])
> + buffer = file.read(32)
read(4)
> + return struct.unpack('>i8', buffer)[0]
'>i'
>
> def read16(self):
> - return np.asscalar(np.fromfile(self.file, count=1, dtype='>i2')[0])
> + buffer = file.read(16)
read(2)
> + return struct.unpack('>i4', buffer)[0]
'>h'
>
> def read8(self):
> - return np.asscalar(np.fromfile(self.file, count=1, dtype='>i1')[0])
> + buffer = file.read(8)
read(1)
> + return struct.unpack('>i2', buffer)[0]
'b'
>
> def readstr(self, len = None):
> + read_format = str(len) + 'd'
> if len is None:
> len = self.read8()
> if len == 0:
> return ""
> - return np.fromfile(self.file, count=1, dtype=('S%d' % len))[0]
> + buffer = file.read(8)
> + return struct.unpack(read_format, buffer[0:(0 +
> struct.calcsize(read_format))])
According to the numpy documentation 'S' produces raw bytes (not a
unicode string). To get the raw bytes we just need file.read(len). The
struct module isn't needed.
Something like this should work:
if len is None:
len = self.read8()
if len == 0:
return ""
return file.read(len).split(b'\0')[0]
>
> def readvar(self, size = None):
> if size is None:
> @@ -303,8 +308,10 @@ class VMSDFieldInt(VMSDFieldGeneric):
>
> def read(self):
> super(VMSDFieldInt, self).read()
> - self.sdata = np.fromstring(self.data, count=1,
> dtype=(self.sdtype))[0]
> - self.udata = np.fromstring(self.data, count=1,
> dtype=(self.udtype))[0]
> + buffer = file.read(self.data)
This statement doesn't make sense. According to the Python
documentation:
read([size]) -> read at most size bytes, returned as a string.
self.data *is* the buffer. There's no need to call file.read().
> + read_format = self.sdtype
Unused.
> + self.sdata = struct.unpack(self.sdtype, buffer[0:(0 +
> struct.calcsize(self.sdtype))])
struct.calcsize() is unnecessary since self.size already contains the
size in bytes.
struct.unpack returns a tuple and we need the first element, so it
should be:
self.sdata = struct.unpack(...)[0]
> + self.sdata = struct.unpack(self.udtype, buffer[0:(0 +
> struct.calcsize(self.udtype))])
The data type specifiers are incorrect because the struct module uses
different syntax than numpy:
self.sdtype = '>i%d' % self.size
self.udtype = '>u%d' % self.size
The struct data type specifiers can be looked up like this:
sdtypes = {1: 'b', 2: '>h', 4: '>i', 8: '>q'}
udtypes = {1: 'B', 2: '>H', 4: '>I', 8: '>Q'}
self.sdtype = sdtypes[self.size]
self.udtype = udtypes[self.size]
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