我正在尝试建立一个系统来处理不明确存在的模块的延迟加载。基本上,我有一个http服务器,其中包含许多我想以编程方式提供导入功能的端点,这些端点我不知道。这些模块都将具有统一的方法签名,只是它们不会提前存在。
import lazy.route as test
import lazy.fake as test2
test('Does this exist?') # This sends a post request.
test2("This doesn't exist.") # Also sends a post request
我可以使用统一的装饰器处理围绕这些导入所需的所有逻辑,我只是找不到在Python中“修饰”导入的任何方式,或者实际上没有以任何编程方式与它们进行交互。
这个事情谁有经验?我一直在寻找,而我发现的最接近的东西是ast
模块,在我目前的理解下,这将导致我目前的一种非常糟糕的实现(类似于查找所有导入语句并手动覆盖导入功能)
不寻找讲义,只是开始学习的一部分python代码库,或者正在做类似事情的人的示例。
我在搜寻时有点聪明,设法找到一个专门解决此问题的PEP,它恰好是相对未知的,可能是因为合理使用它的范围很窄。
我发现了一段出色的示例代码,展示了新的sys.meta_path
实现。我将其发布在下面,以获取有关如何动态引导您的导入语句的信息。
import sys
class VirtualModule(object):
def hello(self):
return 'Hello World!'
class CustomImporter(object):
virtual_name = 'my_virtual_module'
def find_module(self, fullname, path):
"""This method is called by Python if this class
is on sys.path. fullname is the fully-qualified
name of the module to look for, and path is either
__path__ (for submodules and subpackages) or None (for
a top-level module/package).
Note that this method will be called every time an import
statement is detected (or __import__ is called), before
Python's built-in package/module-finding code kicks in."""
if fullname == self.virtual_name:
# As per PEP #302 (which implemented the sys.meta_path protocol),
# if fullname is the name of a module/package that we want to
# report as found, then we need to return a loader object.
# In this simple example, that will just be self.
return self
# If we don't provide the requested module, return None, as per
# PEP #302.
return None
def load_module(self, fullname):
"""This method is called by Python if CustomImporter.find_module
does not return None. fullname is the fully-qualified name
of the module/package that was requested."""
if fullname != self.virtual_name:
# Raise ImportError as per PEP #302 if the requested module/package
# couldn't be loaded. This should never be reached in this
# simple example, but it's included here for completeness. :)
raise ImportError(fullname)
# PEP#302 says to return the module if the loader object (i.e,
# this class) successfully loaded the module.
# Note that a regular class works just fine as a module.
return VirtualModule()
if __name__ == '__main__':
# Add our import hook to sys.meta_path
sys.meta_path.append(CustomImporter())
# Let's use our import hook
import my_virtual_module
print my_virtual_module.hello()
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