CPython学习

前言

Python有时候太慢，如果手动编译C或者是C++来写#include的文件也比较麻烦。
CPython无疑是一个比较好的选择。

简介

CPython是特指C语言实现的Python，就是原汁原味的Python。

之所以使用CPython这个词，是因为Python还有一些其它的实现，比如Jython，就是Java版的Python，还有烧脑的PyPy，使用Python再把Python实现了一遍。

如下是官方对CPython的说明：

CPython is Guido van Rossum’s reference version of the Python computing language. It’s most often called simply “Python”; speakers say “CPython” generally to distinguish it explicitly from other implementations.

案例

先从一个Hello Word开始

1. 创建一个文件helloworld.pyx，内容如下：

    print("Hello world!") #pyx文件是python的c扩展文件，代码要符合cython的规范，用什么编辑器写都行。
   

2. 保存后，创建setup.py文件，内容如下：

    from distutils.core import setup
    from Cython.Build import cythonize
    
    setup(
        ext_modules = cythonize("helloworld.pyx")
    )
   

3. 保存后，进入setup.py所在目录，并执行编译命令：

    python setup.py build_ext --inplace
   

   会输出如下结果：

   $python setup.py build_ext --inplace
   Compiling helloworld.pyx because it changed.
   [1/1] Cythonizing helloworld.pyx
   /anaconda3/envs/deeplearning/lib/python3.7/site-packages/Cython/Compiler/Main.py:369: FutureWarning: Cython directive ‘language_level’ not set, using 2 for now (Py2). This will change in a later release! File: /Users/user/pytorch/NLP学习/learning_2.0/helloworld.pyx
   tree = Parsing.p_module(s, pxd, full_module_name)
   running build_ext
   building ‘helloworld’ extension
   creating build
   creating build/temp.macosx-10.9-x86_64-3.7
   gcc -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I/anaconda3/envs/deeplearning/include -arch x86_64 -I/anaconda3/envs/deeplearning/include -arch x86_64 -I/anaconda3/envs/deeplearning/include/python3.7m -c helloworld.c -o build/temp.macosx-10.9-x86_64-3.7/helloworld.o
   gcc -bundle -undefined dynamic_lookup -L/anaconda3/envs/deeplearning/lib -arch x86_64 -L/anaconda3/envs/deeplearning/lib -arch x86_64 -arch x86_64 build/temp.macosx-10.9-x86_64-3.7/helloworld.o -o /Users/user/pytorch/NLP学习/learning_2.0/helloworld.cpython-37m-darwin.so

4. 运行完这个命令后，该目录下就会生成三个文件：

    build                    helloworld.pyx
    helloworld.c                setup.py
    helloworld.cpython-37m-darwin.so
   

5. 然后创建一个调用文件test.py,内容为：

    import helloworld
   

   运行返回：

    i$ python test.py 
    Hello world!
   

Fibonacci Function项目

斐波那契数列：1, 1, 2, 3, 5,… 前两位为1，之后每个数等于前面两个数之和。

创建fib.pyx，内容如下：

from __future__ import print_function

def fib(n):
    a, b = 0, 1
    while b < n:
        print(b, end=' ')
        a, b = b, a+b
    print()

创建setup.py文件，内容如下：

from distutils.core import setup
from Cython.Build import cythonize

setup(
    ext_modules = cythonize("fib.pyx")
)

通过命令python setup.py build_ext --inplace，生成出来的文件：

python setup.py build_ext --inplace
Compiling fib.pyx because it changed.
[1/1] Cythonizing fib.pyx
/anaconda3/envs/deeplearning/lib/python3.7/site-packages/Cython/Compiler/Main.py:369: FutureWarning: Cython directive 'language_level' not set, using 2 for now (Py2). This will change in a later release! File: /Users/user/pytorch/NLP学习/learning_2.0/fib.pyx
  tree = Parsing.p_module(s, pxd, full_module_name)
running build_ext
building 'fib' extension
gcc -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I/anaconda3/envs/deeplearning/include -arch x86_64 -I/anaconda3/envs/deeplearning/include -arch x86_64 -I/anaconda3/envs/deeplearning/include/python3.7m -c fib.c -o build/temp.macosx-10.9-x86_64-3.7/fib.o
gcc -bundle -undefined dynamic_lookup -L/anaconda3/envs/deeplearning/lib -arch x86_64 -L/anaconda3/envs/deeplearning/lib -arch x86_64 -arch x86_64 build/temp.macosx-10.9-x86_64-3.7/fib.o -o /Users/user/pytorch/NLP学习/learning_2.0/fib.cpython-37m-darwin.so

测试test.py:

import fib
fib.fib(100)

返回：

$ python test.py 
1 1 2 3 5 8 13 21 34 55 89