Update page 'Day 3 homework'

Day 3 homework.md

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+We're going to implement a class, `BoundedInt`, that only allows arithmetic within a given range of integers.  For simplicity, we're only going to support addition and subtraction for now.
+
+Here's the standard class template, which we'll go over in more detail later on.  The test program is here:
+
+https://gogs.gtsplab.com:5432/j/python-test/src/main/test13.py
+
+You can either append it to the template below, or save the template as BoundedInt.py in the same directory and run test13.py to execute the tests.
+
+```
+class BoundedInt():
+    def __init__(self, i, min, max):
+        """
+        Create a bounded integer.
+
+        Args:
+            i (int): The initial value of the integer.
+            min (int): The minimum value of the integer.
+            max (int): The maximum value of the integer.
+        """
+        self.i = i
+        self.min = min
+        self.max = max
+```
+
+1. Read this:
+
+https://docs.python.org/3/reference/datamodel.html?highlight=__int__#object.__int__
+
+Modify the template to pass test 1, which checks that `int()` called on your class will return the value of `i`.
+
+2. Read this, and the paragraph below it: https://docs.python.org/3/reference/datamodel.html?highlight=__int__#object.__add__
+
+What do you think the types of x and y are?  Guess, without checking first.  What are they, actually?  You can use the debugger's local window to find out.
+
+Modify the template to pass test 2, which checks that:
+
+    * Your class implements the + operator.
+    * It throws ValueError when attempting to add two BoundedInts that will exceed the limits.
+
+3. Do the same as 2, but