Python3：传递函数名称作为争论

Question

I am learning python oop concepts and stumbled upon below code that I am trying to write. There is a class Sort which has different methods of sorting and a generic function sort.

class Sort:
    def __init__(self, numlist):
        self.numlist = numlist

    def msort(self, beg, end, reverse=False): #merge sort
        if beg < end:
             mid = (beg + end)//2

             self.msort(beg, mid, reverse)
             self.msort(mid+1, end, reverse)
             self.__merge(beg, mid, end, reverse)


    def isort(self, beg, end, reverse=False): #insertion sort
        i = beg #initial index
        for key in numlist[beg+1:end+1]: #from beg+1 to end
            i = i+1 #current index in numlist
            j = i-1
            if reverse:
                while j >= beg and self.numlist[j] < key:
                    self.numlist[j+1] = self.numlist[j]
                    j = j-1
                self.numlist[j+1] = key
            else:
                while j >= beg and self.numlist[j] > key:
                    self.numlist[j+1] = self.numlist[j]
                    j = j-1
                self.numlist[j+1] = key


    def sort(self, beg, end, func=msort, reverse=False):
        print('Calling {0}()'.format(func))
        func(self, beg, end, reverse)

if __name__ == '__main__':
    numlist = [3, 4, 2, 5, 9, 7, 1, 6]
    s = Sort(numlist)
    s.sort(0, len(numlist)-1, func=isort, reverse=False)
    print(s.numlist, end='')

I have following questions - 1. In main, if I just call s.sort(0, len(numlist)-1, reverse=False) it properly calls msort and gives the result but if I call like s.sort(0, len(numlist)-1, func=isort, reverse=False) it gives below error -

Traceback (most recent call last): File "Sort.py", line 76, in s.sort(0, len(numlist)-1, func=isort, reverse=False) NameError: name 'isort' is not defined

I understand why it doesn't work but not able understand why msort works fine.

2. If I call s.sort(0, len(numlist)-1, func=s.isort, reverse=False) then I get below error -

Calling main.Sort object at 0x031BF830>>() Traceback (most recent call last): File "Sort.py", line 76, in s.sort(0, len(numlist)-1, func=s.isort, reverse=False) File "Sort.py", line 71, in sort func(self, beg, end, reverse) TypeError: isort() takes from 3 to 4 positional arguments but 5 were given

Not able to understand what is happening here. I seems to call isort but why is the parameter mismatch

3. In function sort(), I am not able to call self.func() which again gives attribute error. Is this a bad practice to use self. while calling other function but calling func() without using self.func()?

Please explain pythonic way of organizing this class and function calling.

Answer 1

msort is resolved within the scope of the class definition so it knows it is Sort.msort .

To use isort from outside of defining the class you need to use pass Sort.isort .

When you pass s.isort the method is already bound to the object, so you mustn't pass self as the first parameter.

Answer 2

Your error is that isort is an instance method, which means it does not exist outside the scope of the Sort class. You can reference it by using Sort.isort in your main :

s.sort(0, len(numlist)-1, func=Sort.isort, reverse=False)

The reason you got the second error is that s.isort already adds self (where self is s ) to isort 's argument list. When you call func(self, ...) you are adding self a second time and so you get a total of 5 arguments.

Answer 3

You should change you line func(self, beg, end, reverse) to func(beg, end, reverse) . The self argument is passed automagicly. I'm able to get it working with s.isort.

Answer 4

Thanks for replying. Few things are clear to me. I also found one mistake in above program that in isort function I am using

for key in numlist[beg+1:end+1]:

which actually should be

for key in self.numlist[beg+1:end+1]:

I will summarize the findings below - 1. Calling func(self, beg, end, reverse) works if I pass func=Sort.isort in main 2. Calling func(beg, end, reverse) works If I pass func=s.isort in main

I understood above 2 points well.

3. Calling func(beg, end, reverse) doesn't work if I pass func=Sort.isort in main . It gives me error -

Calling () Traceback (most recent call last): File "Sort.py", line 79, in s1.sort(0, len(numlist)-1, func=Sort.isort, reverse=False) File "Sort.py", line 72, in sort func(beg, end, reverse) File "Sort.py", line 55, in isort for key in self.numlist[beg+1:end+1]: #from beg+1 to end AttributeError: 'int' object has no attribute 'numlist'

I am guessing if self is not first arguement then by default 'int' object is passed in isort. So its cribbing as int doesn't have attribute numlist.

4. Calling self.func(beg, end, reverse) never works no matter how I pass func in main. I tried func=Sort.isort and func=s.isort in main but everytime same attribute error saying

AttributeError: 'Sort' object has no attribute 'func'

Could anyone please confirm my findings?