python_tutorial.md

Python tutorial

##packaging When a submodule is loaded using any mechanism (e.g. importlib APIs, the import or import-from statements, or built-in __import__()) a binding is placed in the parent module’s namespace to the submodule object. For example, if package spam has a submodule foo, after importing spam.foo, spam will have an attribute foo which is bound to the submodule. The invariant holding is that if you have sys.modules['spam'] and sys.modules['spam.foo'] (as you would after the above import), the latter must appear as the foo attribute of the former.

The public names defined by a module are determined by checking the module’s namespace for a variable named __all__; if defined, it must be a sequence of strings which are names defined or imported by that module. The names given in __all__ are all considered public and are required to exist. If __all__ is not defined, the set of public names includes all names found in the module’s namespace which do not begin with an underscore character ('_').

how does function in class becomes to method

class method(object):
    def __init__(self, func, instance, cls):
         self.im_func = func
         self.im_self = instance
         self.im_class = cls

    def __call__(self, *args, **kw):
         # XXX : all sanity checks removed for readability
         if self.im_self:
             args = (self.im_self,) + args
         return self.im_func(*args, **kw)

class function(object):
     def __get__(self, instance, cls):
         return method(self, instance, cls)

All def definitions in class are normal instances of the type function, Foo.print attribute reference will take the following steps.

• method object is initiated with attribute reference by descriptor protocol, e.g. Foo.print(), here the attribute print has a type function which implements descriptor protocol, __get__ method will be called and Foo.print resolves to the return value of the method __get__, which is a object of the type method.
• construct method attribute with method.__init__, storing function name, class instance(self), class object. method is a wrapper object of the function definition with instance object and class object, it will insert the instance object into the argument list of the function when method is called by __call__
• the returned method will be called.

END

• reference 1
• implemnt descriptor
• descriptor