[

1. import_hook

所谓import hook就是指直接自定义finder和loader,并将finder放入导入过程,以实现一些特殊的运行时行为的技巧.

利用这个可以做到很多非常神奇的事情,比如

import某个特定模块时触发某个回调函数来通知我们
import一个远程服务器上的模块
直接import其他语言的模块来使用

本节需要的先验知识包括:

1.1. import hook的基本形式

import hook通常是以一个单文件模块的形式出现的,其中的过程说白了就是自定义finder和loader,因此自定义这两个类都是必须的,然后就是将定义的finder实例化,并将这个实例加入sys.meta_path.下面是模板代码.

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict   class ClientImportLoader(Loader):     @classmethod     def create_module(clz,spec):         """用于创建模块的."""         module = __create_module_from_spec(spec)         return module or None      @classmethod     def exec_module (clz, module):         """每次执行引入模块或者重载模块时会执行的操作"""         pass  loader= ClientImportLoader()   class ClientImportFinder(MetaPathFinder):      @classmethod     def find_spec (klass, full_name, paths=None, target=None):         """查找模块的逻辑"""         pass         return ModuleSpec(full_name, loader, origin=module_full_path)   sys.meta_path.insert(0, ClientImportFinder())

当这个定义import hook的模块被加载后,他就可以正常的执行自己的功能了,因此通常这个import hook的模块需要优先加载.

1.2. import某个特定模块时触发某个回调函数来通知我们

这个例子来自python cookbook,不过上面的代码已经比较过时了,这边给出python3.5+推荐的写法

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder)

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?')

import numpy

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import a

********None

finder._skip

set()

为了避免陷入无线循环,ClientImportFinder维护了一个所有被加载过的模块集合_skip,如果一个模块在加载过程中又有另一个地方来加载,那么就会跳过这个加载器

1.3. import一个远程服务器上的模块

这个例子主要是复写finder以可以查找到目标服务器上的模块文件.同时复写loader的create_module方法用远端的代码生成服务.

我们的远程代码以http服务的形式放在静态服务器上

testcode-|          |-spam.py          |-fib.py          |-grok-|                 |-__init__.py                 |-blah.py

spam.py

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 0

fib.py

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 1

grok/__init__.py

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 2

grok/blah.py

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 3

使用python自带的http服务启动:

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 4

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 5

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 6

1.3.1. 最简单的方法

这个流程也描述了最通用的模块导入流程.我们可以使用imp.new_module新建一个空的模块对象,再使用内置方法compile()将源码编译到一个代码对象中,然后在模块对象的字典中来执行它.

这种方式没有嵌入到通常的import语句中,如果要支持更高级的结构比如包就需要更多的工作了.

下面是使用这个函数的方式:

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 7

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 8

import importlib from importlib.abc import (     MetaPathFinder,      PathEntryFinder,     Loader ) from importlib.machinery import ModuleSpec import sys from collections import defaultdict  _post_import_hooks = defaultdict(list)  class ClientImportLoader(Loader):     def __init__(self, finder):         self._finder = finder       def create_module(self,spec):         """这边只要调用父类的实现即可."""         return super().create_module(spec)      def exec_module (self, module):         """在_post_import_hooks中查找对应模块中的回调函数并执行."""         for func in _post_import_hooks[module.__name__]:             func(module)         self._finder._skip.remove(module.__name__)  class ClientImportFinder(MetaPathFinder):      def __init__(self):         self._skip = set()      def find_spec(self, full_name, paths=None, target=None):         if full_name in self._skip:             return None         self._skip.add(full_name)         loader = ClientImportLoader(self)         return ModuleSpec(full_name, loader, origin=paths)   def when_imported(fullname):     def decorate(func):         if fullname in sys.modules:             func(sys.modules[fullname])         else:             _post_import_hooks[fullname].append(func)         return func     return decorate  finder = ClientImportFinder() sys.meta_path.insert(0, finder) 9

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 0

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 1

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 2

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 3

1.3.2. 使用 import hook实现隐式调用远端模块

如果我们想要导入文件系统中某个文件作为模块,我们会这样写以确保文件目录Python解释器可以找到.

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 4

我们希望远端的也可以实现这种与标准流程统一的方式,这时候就需要使用import hook了.

因为访问的地址和文件系统不同,因此可以使用sys.path_hooks为这个特定的地址设置一个finder

此处我们需要

定义finder
定义loader
定义handle_url()函数作为钩子

sys.path_hooks.append(handle_url)变量中注册着查找sys.path的钩子,当sys.path的实体被处理时会调用sys.path_hooks中的函数.如果任何一个函数返回了一个finder,那么这个对象就被用来为sys.path实体加载模块.

这个例子完全使用标准库实现

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 5

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 6

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 7

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 8

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 9

import numpy 0

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 7

import numpy 2

import numpy 3

@when_imported('numpy') def warn_numpy(mod):     print('numpy? Are you crazy?') 7

import numpy 5

import numpy 6

1.4. 直接import其他语言的模块来使用

一个更加酷的用法是直接导入别的语言的代码成为模块.这有两种途径

通过一个自定义的编译器将源码编译为python可以直接import的动态链接库,之后再导入这个动态链接库
通过一个自定义的语法解释器将特定源码转化为python对象

1.4.1. 导入Fortran代码作为模块

这个例子我们来尝试第一种方法,其基本流程是:

定义一个finder用于找到以.f,.f90或者.f95位后缀的文件作为源文件

需要注意的这个需求依然会用到文件系统,Fortran的源码很大的可能性与python的原生源文件共存,因此不适合使用sys.path_hook.
使用numpy中自带的工具f2py来实现Fortran代码的编译工作

f2py无法指定输出的动态链接库位置,需要进一步的文件系统操作.这边可以利用标准库Pathlib和shutil

将编译成功后的动态链接库导入到程序中.

需要注意引入动态链接库时不能使用import或者__import__或者importlib.import_module这些直接生成完整模块对象的方式,否则会递归调用. 此处应该使用如下的方式借由生成spec来生成模块.
```
import numpy 7
```
再借由这个spec的loader来执行模块
```
import numpy 8
```

当然了这个例子并没有考虑fortain本身的语法和多文件编译的问题,可能还会有些问题.

import numpy 9

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