Hi guys, I'm working on problem set 9, question 2. In the very last part of the question we are supposed to implement __str__ for the ShapeSet class, which prints the string representation of each object in the ShapeSet class. I can't figure out how to do this correctly. Here is my code:
class ShapeSet:
def __init__(self):
self.shapes=[]
#Skipping some irrelevant functions...
def __str__(self):
for shape in self.shapes:
print shape
When I do the same thing in the main program (use a for loop to print each object in the ShapeSet class

Question

Hi guys, I'm working on problem set 9, question 2. In the very last part of the question we are supposed to implement  __str__ for the ShapeSet class, which prints the string representation of each object in the ShapeSet class. I can't figure out how to do this correctly. Here is my code:
class ShapeSet:
    def __init__(self):
        self.shapes=[]
#Skipping some irrelevant functions...
    def __str__(self):
           for shape in self.shapes:
              print shape
When I do the same thing in the main program (use a for loop to print each object in the ShapeSet class

anonymous · Answer

sorry ran out of room...
it works correctly, but when I do it within the ShapeSet class I get a TypeError: __str__ returned non-string (type NoneType) . I'm not sure what I am doing wrong...can anyone help?

anonymous · Answer

what you posted looks ok - use a code pasting site and post all your classes
the error gives a clue it says that None was returned - what 'command' or statement produced that?

try changing the for loop to
return '
'.join([str(thing) for thing in self.shapes])
then as long as shapes contains objects with a __str__ function, print shapeset should work

those magic functions (__xxx__) should return something - not do something.