我正在重写HTMLCalendar类中的方法。 但它给了我一个错误。 我该如何正确地继承这个？

Question

    class foo(HTMLCalendar):
        def formatday(self, day, weekday, data):
            if day==0
                return '<td class="noday">&nbsp;</td>'

            else:
                return '<td class="%s">%d %s</td>' % (self.cssclasses[weekday], day, data)

    a = foo()
    a.formatmonth(1, 2)

Whenever I try that it gives me an error saying formatday() takes exactly 4 arguments (3 given). I am trying to overide the formatday method so that I can put some data in it. Can someone tell me what I am doing wrong here?

Answer 1

Your problem here is that formatmonth calls formatday, and you're not overriding formatmonth, so formatmonth uses the regular arguments for formatday, ie, just day and weekday.

If you don't want the data there for formatmonth, then you could just give data a default value, eg:

class foo(HTMLCalendar):
    def formatday(self, day, weekday, data=''):
        if day==0: # note error here in original code
            return '<td class="noday">&nbsp;</td>'
        else:
            return '<td class="%s">%d %s</td>' % (self.cssclasses[weekday], day, data)

a = foo()
a.formatmonth(1, 2)

If you do want the data there, then your options depend on what that data is. Is it supposed to be the same for each day in the month being formatted? If so, then you could override formatmonth as well, or you could have the data be an instance variable, eg, take it from a self.data that could then be set with a.data = ... . If it changes for each day, you probably should have formatday get that data from somewhere else, rather than simply having it as an argument.

In general, overriding a method with a method that requires extra arguments, or has some incompatible API, is dangerous. Anything you don't override that calls that method will break.