如果您对将numpy.frombuffer与JPyjava字节数组一起使用会导致随机输出和numpyfromstring感兴趣，那么这篇文章一定是您不可错过的。我们将详细讲解将numpy.frombu

如果您对将 numpy.frombuffer 与 JPy java 字节数组一起使用会导致随机输出和numpy fromstring感兴趣，那么这篇文章一定是您不可错过的。我们将详细讲解将 numpy.frombuffer 与 JPy java 字节数组一起使用会导致随机输出的各种细节，并对numpy fromstring进行深入的分析，此外还有关于"import numpy as np" ImportError: No module named numpy、3.7Python 数据处理篇之 Numpy 系列 (七)---Numpy 的统计函数、Anaconda Numpy 错误“Importing the Numpy C Extension Failed”是否有另一种解决方案、Difference between import numpy and import numpy as np的实用技巧。

• 将 numpy.frombuffer 与 JPy java 字节数组一起使用会导致随机输出（numpy fromstring）
• "import numpy as np" ImportError: No module named numpy
• 3.7Python 数据处理篇之 Numpy 系列 (七)---Numpy 的统计函数
• Anaconda Numpy 错误“Importing the Numpy C Extension Failed”是否有另一种解决方案
• Difference between import numpy and import numpy as np

将 numpy.frombuffer 与 JPy java 字节数组一起使用会导致随机输出（numpy fromstring）

如何解决将 numpy.frombuffer 与 JPy java 字节数组一起使用会导致随机输出

我使用 JPy 作为 Java 和 Python 之间的桥梁。我从Java端启动程序。当我从 Java 端将字节数组 (byte[]) 作为参数传递给 Python 函数并将其转换为 numpy 数组时，np.frombuffer 的结果将有前 16 个字节不正确（并且其他字节是正确的）。但是，只有当数组的长度超过 392 字节时才会出现此问题。下面是一些重现它的示例代码：

Java 代码 (JPyTest.java)

import java.util.Arrays;
import org.jpy.PyLib;
import org.jpy.PyModule;
import org.jpy.PyObject;
import com.tocaya.utils.TocayaUtils;
public class JPyTest {
    public interface Processor {
        byte[] byte_array(byte[] array);
    }
    public static void main(String[] args) {
        //Setup JPy stuff
        PyLib.startPython(TocayaUtils.substituteEnvVars("put path to proc_class.py here"));
        PyModule procModule = PyModule.importModule("proc_class");
        PyObject procObj = procModule.call("Processor");
        Processor processor = procObj.createProxy(Processor.class);
        //Define a byte array with length of 392
        byte[] goodBytes = new byte[] {0,-93,-96,51,65,-48,118,-65,29,31,-92,-32,63,-87,-66,17,57,-63,-81,-35,-117,-102,-43,-101,-30,-24,81,-23,-16,6,1,-40,-1,111,119,79,-97,-28,-51,-8,-100,77,-72,-34,-9,11,47,-53,40,-58,125,8,-59,99,-13,-26,-75,-67,10,23,-38,-17,95,-5,-4,-126,-105,25,28,-36,53,-46,-44,64,96,-80,39,35,37,-55,30,120,-120,92,-45,19,22,-12,-113,-99,-127,-68,-89,-112,36,82,-78,-31,61,55,48,-33,-14,9,80,-18,-39,3,-54,-20,106,43,85,71,-95,-41,-73,113,105,-88,117,78,108,32,-103,21,-60,-25,41,-121,20,107,-10,94,-86,26,122,73,116,-110,69,68,-50,-6,-49,74,112,-47,-90,49,13,-37,-85,44,-111,-21,72,-27,-114,24,-74,60,-11,-124,-22,86,83,-3,100,90,75,16,-19,14,-69,63};
        
        System.out.println("good bytes len = " + goodBytes.length);
        
        //Call the python function via JPy
        byte[] outBytes = processor.byte_array(goodBytes);
        System.out.println("good bytes output = " + Arrays.toString(outBytes));
        System.out.println("----------------------");
        //Define an array of bytes that has length of 393
        byte[] badBytes = Arrays.copyOf(goodBytes,goodBytes.length+1);
        System.out.println("bad bytes len = " + badBytes.length);
        //Call the python function via JPy
        outBytes = processor.byte_array(badBytes);
        System.out.println("bad bytes output = " + Arrays.toString(outBytes));
        
        PyLib.stopPython();
    }
}

Python 代码 (proc_class.py)

class Processor:
    def __init__(self):
        pass
        
    def byte_array(self,array):
        import numpy as np
        print(f''first 24 bytes in python before np.frombuffer {",".join(str(array[i]) for i in range(24))}'')
        out = np.frombuffer(array,dtype=np.dtype("b")).tobytes()
        print(f''first 24 bytes in python after np.frombuffer {",".join(str(int.from_bytes(out[i:i+1],byteorder="little",signed=True)) for i in range(24))}'')
        return out

Java 输出

E:\\Warez\\Development\\Javabin\\jpy-0.10.0\\jpy.cp37-win_amd64.pyd
good bytes len = 392
good bytes output = [0,63]
----------------------
bad bytes len = 393
bad bytes output = [-48,-122,0]

Python 输出

first 24 bytes in python before np.frombuffer 0,63
first 24 bytes in python after np.frombuffer 0,63
first 24 bytes in python before np.frombuffer 0,63
first 24 bytes in python after np.frombuffer -48,63

如您所见，对于第二个字节数组 badBytes（长度为 393），np.frombuffer 的前 16 个字节的输出不正确。我已经用其他长度进行了测试，只有/总是当字节数组大于 392 字节时才会出现问题。

版本

• Python 3.7.4
• 操作系统 Windows 8.1
• Java 1.8.0_281
• JPy 0.10.0.dev1（截至 2021 年 1 月 26 日在 GitHub 上的最新主版本）

"import numpy as np" ImportError: No module named numpy

问题：没有安装 numpy

解决方法：

下载文件，安装

numpy-1.8.2-win32-superpack-python2.7

安装运行 import numpy，出现

Traceback (most recent call last):
  File "<pyshell#2>", line 1, in <module>
    import numpy
  File "C:\Python27\lib\site-packages\numpy\__init__.py", line 153, in <module>
    from . import add_newdocs
  File "C:\Python27\lib\site-packages\numpy\add_newdocs.py", line 13, in <module>
    from numpy.lib import add_newdoc
  File "C:\Python27\lib\site-packages\numpy\lib\__init__.py", line 8, in <module>
    from .type_check import *
  File "C:\Python27\lib\site-packages\numpy\lib\type_check.py", line 11, in <module>
    import numpy.core.numeric as _nx
  File "C:\Python27\lib\site-packages\numpy\core\__init__.py", line 6, in <module>
    from . import multiarray
ImportError: DLL load failed: %1 不是有效的 Win32 应用程序。

原因是：python 装的是 64 位的，numpy 装的是 32 位的

重新安装 numpy 为：numpy-1.8.0-win64-py2.7

3.7Python 数据处理篇之 Numpy 系列 (七)---Numpy 的统计函数

目录

[TOC]

前言

具体我们来学 Numpy 的统计函数

（一）函数一览表

调用方式：np.*

（二）统计函数 1

（1）说明

（2）输出

.sum(a)

.mean(a)

.average(a)

.std(a)

.var(a)

（三）统计函数 2

（1）说明

（2）输出

.max(a) .min(a)

.ptp(a)

.median(a)

.argmin(a)

.argmax(a)

.unravel_index(index,shape)

作者：Mark

日期：2019/02/11 周一

Anaconda Numpy 错误“Importing the Numpy C Extension Failed”是否有另一种解决方案

  \Traceback (most recent call last):
File "C:\Conda\envs\gcp\lib\site-packages\numpy\core\__init__.py",line 22,in <module>
from . import multiarray
File "C:\Conda\envs\gcp\lib\site-packages\numpy\core\multiarray.py",line 12,in <module>
from . import overrides
File "C:\Conda\envs\gcp\lib\site-packages\numpy\core\overrides.py",line 7,in <module>
from numpy.core._multiarray_umath import (
ImportError: DLL load Failed while importing _multiarray_umath: The specified module Could not be found.

During handling of the above exception,another exception occurred:

Traceback (most recent call last):
File "c:\API\citi-bike.py",line 4,in <module>
import numpy as np
File "C:\Conda\envs\gcp\lib\site-packages\numpy\__init__.py",line 150,in <module>
from . import core
File "C:\Conda\envs\gcp\lib\site-packages\numpy\core\__init__.py",line 48,in <module>
raise ImportError(msg)
ImportError:

IMPORTANT: PLEASE READ THIS FOR ADVICE ON HOW TO SOLVE THIS ISSUE!

Importing the numpy C-extensions Failed. This error can happen for
many reasons,often due to issues with your setup or how NumPy was
installed.

We have compiled some common reasons and troubleshooting tips at:

https://numpy.org/devdocs/user/troubleshooting-importerror.html

Please note and check the following:

* The Python version is: python3.9 from "C:\Conda\envs\gcp\python.exe"
* The NumPy version is: "1.21.1"

and make sure that they are the versions you expect.
Please carefully study the documentation linked above for further help.

Original error was: DLL load Failed while importing _multiarray_umath: The specified module Could not be found.

import numpy as np

import numpy.f2py as myf2py

import numpy as np
np.f2py #throws no module named f2py

import numpy as np # np is an alias pointing to numpy, but at this point numpy is not linked to numpy.f2py
import numpy.f2py as myf2py # this command makes numpy link to numpy.f2py. myf2py is another alias pointing to numpy.f2py as well

import numpy

import numpy as np

import numpy
np = numpy
del numpy

import numpy as np
import numpy.f2py   # OK
import np.f2py      # ImportError

import scipy.ndimage.interpolation as warp
warp.affine_transform(I, ...)

try:
    import pyfftw.interfaces.numpy_fft as fft
except:
    import numpy.fft as fft
# call fft.ifft(If) with fftw or the numpy fallback under a common name

import numpy as np
np.f2py