1. Importer協議

協議涉及兩個對象： Finder 和 loader

1. Finder

實現了方法：

finder.find_module(fullname, path=None)

返回一個loader對象或者None。

2. Loader

實現了方法:

loader.load_module(fullname)

返回一個module對象或者raise an exception

2. 注冊hooks

hooks有兩種，一種是Meta hooks，一種是Path hooks。

注冊方式：

import importlib.machinery

import sys

# For illustrative purposes only.

SpamMetaPathFinder = importlib.machinery.PathFinder

SpamPathEntryFinder = importlib.machinery.FileFinder

loader_details = (importlib.machinery.SourceFileLoader,

importlib.machinery.SOURCE_SUFFIXES)

# Setting up a meta path finder.

# Make sure to put the finder in the proper location in the list in terms of

# priority.

sys.meta_path.append(SpamMetaPathFinder)

# Setting up a path entry finder.

# Make sure to put the path hook in the proper location in the list in terms

# of priority.

sys.path_hooks.append(SpamPathEntryFinder.path_hook(loader_details))

3. 流程

import importlib.util

import sys

def import_module(name, package=None):

"""An approximate implementation of import."""

absolute_name = importlib.util.resolve_name(name, package)

try:

return sys.modules[absolute_name] # 先查詢sys.modules

except KeyError:

pass

path = None

if '.' in absolute_name:

parent_name, _, child_name = absolute_name.rpartition('.')

parent_module = import_module(parent_name)

path = parent_module.__spec__.submodule_search_locations

for finder in sys.meta_path: # 再從sys.meta_path中獲取finder

spec = finder.find_spec(absolute_name, path)

if spec is not None:

break

else:

msg = f'No module named {absolute_name!r}'

raise ModuleNotFoundError(msg, name=absolute_name)

module = importlib.util.module_from_spec(spec)

spec.loader.exec_module(module)

sys.modules[absolute_name] = module

if path is not None:

setattr(parent_module, child_name, module)

return module

其中:

sys.meta_path[-1]類型是, 這個對象調用了sys.path以及sys.path_hooks。

注意：

本來按照pep302的導入邏輯，是：

for mp in sys.meta_path:

loader = mp(fullname)

if loader is not None:

= loader.load_module(fullname)

for path in sys.path:

for hook in sys.path_hooks:

try:

importer = hook(path)

except ImportError:

# ImportError, so try the other path hooks

pass

else:

loader = importer.find_module(fullname)

= loader.load_module(fullname)

# Not found!

raise ImportError

但后來(python3.4)引入了pep451, 接口名和調用方式發生了一些變化，使得流程如3所示。

總結

以上是生活随笔為你收集整理的python importlib_学习python importlib的导入机制的全部內容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網站內容還不錯，歡迎將生活随笔推薦給好友。