python中的类和方法。 oop介绍

Question

class Person:
    def __init__(self, name):
        """Make a new person with the given name."""
        self.myname = name

    def introduction(myname):
        """Returns an introduction for this person."""
        return "Hi, my name is {}.".format(myname)

# Use the class to introduce Mark and Steve
mark = Person("Mark")
steve = Person("Steve")

print(mark.introduction())
print(steve.introduction())

its suppose to produce "Hi, my name is Mark." or "Hi, my name is Steve."

but instead it produces "Hi, my name is undefined."

Answer 1

It should be printing the object's representation in memory (something along the lines of Hi, my name is <__main__.Person object at 0x005CEA10> ).

The reason is that the first argument of a method is expected to be the object that the method is called upon.

Just like you have def __init__(self, name): you should have def introduction(self, myname): .

Then you will encounter another problem, as introduction now expects an argument myname which you don't provide it. You don't actually need it since you now have access to self.myname .

class Person:
    def __init__(self, name):
        """Make a new person with the given name."""
        self.myname = name

    def introduction(self):
        """Returns an introduction for this person."""
        return "Hi, my name is {}.".format(self.myname)


# Use the class to introduce Mark and Steve
mark = Person("Mark")
steve = Person("Steve")

print(mark.introduction())
print(steve.introduction())

Will output

Hi, my name is Mark.
Hi, my name is Steve.

Answer 2

You need to declare introduction() -> introduction(self) as an instance method ( by passing in self ) to be able to access the instance variable self.myname .

class Person:

    def __init__(self, name):
        """Make a new person with the given name."""
        self.myname = name

    def introduction(self):
        """Returns an introduction for this person."""
        return "Hi, my name is {}.".format(self.myname)

Sample output:

# Use the class to introduce Mark and Steve
mark = Person("Mark")
steve = Person("Steve")

print(mark.introduction())
print(steve.introduction())
>>> Hi, my name is Mark.
>>> Hi, my name 

Please note however, that the first parameter in a function within a class is reserved for either a class, or object to pass itself to ( unless a @staticmethod tag is applied to the method, then the first implicit parameter is not passed; which essentially behave as module methods ).

Also keep in mind that self is not a reserved word, so you could name it anything ( even though self is PEP convention ). The below example executes the same output as the example above, and is semantically the same.

def introduction(myname):
    """Returns an introduction for this person."""
    return "Hi, my name is {}.".format(myname.myname)

9.3.5. Class and Instance Variables

Answer 3

Your problem is that your giving your introduction method the parameter myname , but never supplying it with a valid argument.You can simply do:

mark = Person(" Mark")
steve = Person(" Steve")

print(mark.introduction(mark.myname))
print(steve.introduction(steve.myname))

your giving the introduction method, the variable from your class myname .

But the above is not even necessary. Since your initializing your name variable in the __init__ method of your class, it is like a global variable. So you can simply say:

class Person:
    def __init__(self, name):
        """Make a new person with the given name."""
        self.myname = name

    def introduction(self):
        """Returns an introduction for this person."""
        return "Hi, my name is{}".format(self.myname)


# Use the class to introduce Mark and Steve
mark = Person(" Mark")
steve = Person(" Steve")

print(mark.introduction())
print(steve.introduction())