python核心编程第4章课后题答案（第二版75页）

4-1Python objects

　　All Python objects have three attributes:type,ID,and value.

　　All are readonly with a possible expection of the value(which can be changed only if the object is mutable).

4-5str()and repr()

　　repr() is a built-in function while str() was a built-in function that changed to a factory function inPython2.2.They will both returns a string representation of an object;however,str()returns a printable string representation while repr() returns an evaluatable string representation of an object,meaning that it is astring that represents a Python object that would be created if passed to eval().

4-6Object equality

　　type(a) == type(b) 　　whether the value of type(a) is the same as the value of type(b)... == is a value compare
　　type(a) is type(b) 　　  whether the type objects returned by type(a) and type(b) are the same object
　　Since there exists only one (type) object for each built-in type, there is no need to check their values; hence, only the latter form should be used.

　　isinstance(object, class-or-type-or-tuple) -> bool

　　　　Return whether an object is an instance of a class or of a subclass thereof.
　　　　With a type as second argument, return whether that is the object's type.
　　　　The form using a tuple, isinstance(x, (A, B, ...)), is a shortcut for
　　　　isinstance(x, A) or isinstance(x, B) or ... (etc.).