延迟加载Python模块的最佳实践 [英] Best practice for lazy loading Python modules

问题描述

偶尔我想在Python中加载惰性模块。通常，因为我想保持运行时需求或启动时间低，并将代码分成子模块将是麻烦的。一个典型的用例和我目前的首选实现是：

Occasionally I want lazy module loading in Python. Usually because I want to keep runtime requirements or start-up times low and splitting the code into sub-modules would be cumbersome. A typical use case and my currently preferred implementation is this:

jinja2 = None

class Handler(...):
    ...
    def render_with_jinja2(self, values, template_name):
        global jinja2
        if not jinja2:
            import jinja2
        env = jinja2.Environment(...)
        ...

有没有理由/更好的方法来实现延迟模块加载？

I wonder: is there a canonical/better way to implement lazy module loading?

推荐答案

VM维护已经导入的模块的列表，并且任何后续尝试导入该模块导致sys.modules中的快速dict查找，而没有别的。

There's no reason for you to keep track of imports manually -- the VM maintains a list of modules that have already been imported, and any subsequent attempts to import that module result in a quick dict lookup in sys.modules and nothing else.

您的代码和

def render_with_jinja2(self, values, template_name):
    import jinja2
    env = jinja2.Environment(...)

$ b b

为零 - 当我们点击该代码时，如果 jinja2 未导入，则会导入。如果已经存在，则继续执行。

is zero -- when we hit that code, if jinja2 hasn't been imported, it is imported then. If it already has been, execution continues on.

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