2019独角兽企业重金招聘Python工程师标准>>> 
之前写过一篇关于循环引用import问题
http://my.oschina.net/1123581321/blog/176351
这里换一种方式,增加缓存,解决每次都要import效率低的问题
利用__getattr__实现python的lazy import
class LazyImport(object):
"""使用
os = LazyImport("os", globals(), locals()) # 此时还未导入os,这一行可以写在文件开始,import区域
os.getpid() # 调用__getattr__导入/从cache里获取
"""
def __init__(self, name, globals={}, locals={}, fromlist=[], level=-1):
self.cache = {}
self.mod_name = name
self.globals = globals
self.locals = locals
self.fromlist = fromlist
self.level = level
def __getattr__(self, name):
mod = self.cache.get(self.mod_name)
if not mod:
mod = __import__(self.mod_name, self.globals, self.locals, self.fromlist, self.level)
self.cache[self.mod_name] = mod
return getattr(mod, name)