我想构建一个调用所请求的bulit-in函数的源代码的函数，例如
def recall_source_of_built_in(sum()):
#look up the directory of where the source codes are listed in windows
#find the function whetehr it exists
#if exists, open/read/ and display it on my Shell
要建立这个功能，我必须从哪里开始？