How does setxattr in memory.py change anything?

Question

I'm using memory.py from fusepy (http://code.google.com/p/fusepy/source/browse/trunk/memory.py) for a programming assignment.

How does setxattr (line 87) actually accomplish anything? self.files isn't modified in any way and attrs is destroyed when the function exits.

Answer 1

def setxattr(self, path, name, value, options, position=0):
    # Ignore options
    attrs = self.files[path].setdefault('attrs', {})
    attrs[name] = value

The side-effect is achieved by setdefault, which creates a new item in self.files[path] (unless attrs already exists as a key in it), and returns a reference to the value.

Next, that reference is modified, by assigning to its key name, the value value. By that operation too, self.files is modified.