python基础-动态加载lazy_import（利用__import__）

看了一天动态加载，普遍有这么几种方法，总结一下，由简入深，本文仅对查到的栗子们做个引用……省去你们大把查资料的时间＝ ＝

主要思想：把模块(文件)名、类名、方法名当成了变量 然后利用__import__和getattr实现调用。

注意下getattr()和__getattr__区别：

• getattr()：getattr(obj, “method”)(args)
• __getattr__：调用方法调用不到时，会调用当前类中的__getattr__方法，返回值或AttributeError异常

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1、网上大多举栗子都是这么写的= =。。。

#file: lazy_import/module1.py
class A(object):
    def aa(self):
        print "aa"

    def bb(self, i, j):
        return i+j

　　

#file: lazy_import/test1.py
#coding=UTF-8
def main():
    module_name = "module1"
    class_name = "A"
    method = "aa"

    imp_module = __import__(module_name)
    imp_class = getattr(imp_module, class_name)
    obj = imp_class()
    print "#module:", imp_module
    print "#class:", imp_class
    print "#obj:", obj

    imp_method = getattr(obj, method)
    print "#method:", imp_method
    imp_method()  # call def, 与 imp_method = getattr(obj, method)一起作用，相当于obj.aa()

    imp_method_bb = getattr(obj, "bb")
    ret = imp_method_bb(1, 2)
    print "#ret:", ret

if __name__ == '__main__':
    main()

　　

python lazy_import/test1.py
#module: <module 'module1' from '/xxxxx/lazy_import/module1.pyc'>
#class: <class 'module1.A'>
#obj: <module1.A object at 0x107cf1710>
#method: <bound method A.aa of <module1.A object at 0x107cf1710>>
aa
#ret: 3

　　

2、还发现另外一个栗子这个博主原创

class LazyImport:
    def __init__(self, module_name):
        self.module_name = module_name
        self.module = None  

    def __getattr__(self, funcname):
        if self.module is None:
            self.module = __import__(self.module_name)
            print(self.module)
        return getattr(self.module, funcname)  

a = LazyImport('string')
print(a.lower("WEW")) #'wew'

　　

3、还有这个栗子这个博主原创

#file: lazy_import/module2.py
def test(s, e):
    print "in test func...", s, e

class C(object):
    def __init__(self, name):
        print "in C class init...", name

    def cc(self):
        print 'in C class cc func'

　　

#file: lazy_import/test2.py
class Dynload(object):
    def __init__(self, package):
        self.package = package

    def getobject(self):
        # return __import__(self.package, globals(), locals(), [], -1)
        return __import__(self.package) # import module

    def get_class_instance(self, class_name, *args):
        return getattr(self.getobject(), class_name)(*args)

    def get_class_func(self, instance, method, *args):
        return getattr(instance, method)(*args)

    def get_func(self, method, *args):
        return getattr(self.getobject(), method)(*args)

if __name__ == '__main__':
    dyn = Dynload('module2')
    print "module=", dyn
    # module= <__main__.Dynload object at 0x10f450150>
    # 是一个Dynload对象
    # 直接__import__(module2)时，会返回<module 'module2' from '/xxxxx/lazy_import/module2.pyc'>

    dyn.get_func('test', 'Hello', 'function!')

    ins = dyn.get_class_instance('C', 'Tom')
    dyn.get_class_func(ins, 'cc')