查看模块帮助文档：
- help(len) -- docs for the built in len function (note here you type "len" not "len()" which would be a call to the function)
- help(sys) -- overview docs for the sys module (must do an "import sys" first)
- dir(sys) -- dir() is like help() but just gives a quick list of the defined symbols
- help(sys.exit) -- docs for the exit() function inside of sys
- help('xyz'.split) -- it turns out that the module "str" contains the built-in string code, but if you did not know that, you can call help() just using an example of the sort of call you mean: here 'xyz'.foo meaning the foo() method that runs on strings
- help(list) -- docs for the built in "list" module
- help(list.append) -- docs for the append() function in the list module