setitem and getitem -- python

Question

I've created a python program that makes a vector. Now i want to set an item using a function__setitem__ and__getitem__. So for example, ifvector = Vec()andvector[3] = 26would change an empty vector to[0, 0, 0, 26]. I need to override the__getitem__and__setitem__ I've listed the code below, but i'm having troubles with the get and set functions. Any advice?

class Vec:     def __init__(self, length = 0):         self.vector = [0]*length      def __str__(self):         return '[{}]'.format(', '.join(str(i) for i in self.vector))         #This formats the output according to the homework.         #Adds '[' and ']' and commas between each 0      def __len__(self):         return len(self.vector)      def extend(self, newLen):         self.vector.append([0]*newLen)         return (', '.join(str(j) for j in self.vector))      def __setitem__(self, key, item):         self.vector[key] = item      def __getitem__(self, key):         return self.vector[key] 

Answer 1

You have several problems:

1. extend is appending essentially a new vector to the end of the original, rather than increasing the length of the original. It's not clear that it needs to return a string representation of the modified vector (unless it's just for debugging purposes).

   def extend(self, newlength):     # Assume newlength is greater than the old     self.vector.extend([0] * (newlength - len(self))) 

2. __setitem__ needs to call extend if the key is too large.

   def __setitem__(self, key, item):     if key >= len(self):         self.vector.extend(key+1)     self.vector[key] = item 

3. __getitem__ needs to access the underlying list, not use an undefined attribute

   def __getitem__(self, key):     # It's probably better to catch any IndexError to at least provide     # a class-specific exception     return self.vector[key]