Cookbook 6.2 defines Constants

Task:

Some module-level variables (such as named constants) need to be defined, and the customer Code cannot re-bind them;

Solution:

#coding = utf-8class _const(object):    class ConstError(TypeError): pass    def __setattr__(self,name,value):        if name in self.__dict__:            raise self.ConstError,"Can‘t rebind const(%s)" % name        self.__dict__[name] = value    def __delattr__(self,name):        if name in self.__dict__:            raise self.ConstError,"Can‘t unbind const(%s)" % name        raise NameError,name    import syssys.modules[__name__] = _const()

Usage:

1. Save the preceding code as Const. py and add the directory of the file to the SYS. Path directory;

2. Run Const. py.

3. input the following in Python shell:

Import const

# Test code

Const. Magic = 23

Note: currently, any customer code can import const and bind one attribute of the const module once, but only once;

Once an attribute has been bound, the program cannot rebind it or unbind it.

Const. Magic = 99 # Throw Const. consterror

Del Const. Magic # Throw Const. consterror

 

Cookbook 6.2 defines Constants