为什么函数的 (self, index) 的索引没有在函数内部被调用并且函数仍然有效？

Question

I have this snippet of working and tested Python code:

def renameFiles(self, index):
    filename = self._filenames[self._current_index]
    newFilename = self.createNewFilename()
    self.currentFileName.setText(newFilename)
    dirname = os.path.dirname(filename)
    fullPath = os.path.join(dirname, newFilename)
    os.replace(filename,fullPath)
    self._filenames[self._current_index] = fullPath
    self.current_index = self._current_index

Why is it that the index in the def renameFiles(self, index): isn't called in anywhere inside the function and yet the function still works? (It may not be the most optimized and beautiful code, but still works)

I've searched for manuals and guides for hours now and still can't wrap my head around this. And I can't progress in my project until I understand how this works.

I'll gladly post more of the code if needed.

Answer 1

In python, a user-defined function can have as many "non-callable" arguments as you want. For example, the following is a valid function:

def f(a, b, c, d, e):
    print("Hello World")

However, unless you provide default values for variables a through e, calling the function without specifying them will raise an exception