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Exercises/soln2_4.md

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+# Exercise 2.4 - Solution
+
+```python
+# mutint.py
+
+from functools import total_ordering
+
+@total_ordering
+class MutInt:
+    __slots__ = ['value']
+
+    def __init__(self, value):
+        self.value = value
+
+    def __str__(self):
+        return str(self.value)
+    
+    def __repr__(self):
+        return f'MutInt({self.value!r})'
+
+    def __format__(self, fmt):
+        return format(self.value, fmt)
+
+    # Implement the "+" operator. Forward operands (MutInt + other)
+    def __add__(self, other):
+        if isinstance(other, MutInt):
+            return MutInt(self.value + other.value)
+        elif isinstance(other, int):
+            return MutInt(self.value + other)
+        else:
+            return NotImplemented
+
+    # Support for reversed operands (other + MutInt)
+    __radd__ = __add__
+
+    # Support for in-place update (MutInt += other)
+    def __iadd__(self, other):
+        if isinstance(other, MutInt):
+            self.value += other.value
+            return self
+        elif isinstance(other, int):
+            self.value += other
+            return self
+        else:
+            return NotImplemented
+
+    # Support for equality testing
+    def __eq__(self, other):
+        if isinstance(other, MutInt):
+            return self.value == other.value
+        elif isinstance(other, int):
+            return self.value == other
+        else:
+            return NotImplemented
+
+    # One relation is needed for @total_ordering decorator. It fills in others
+    def __lt__(self, other):
+        if isinstance(other, MutInt):
+            return self.value < other.value
+        elif isinstance(other, int):
+            return self.value < other
+        else:
+            return NotImplemented
+
+    # Conversions to int() and float()
+    def __int__(self):
+        return int(self.value)
+
+    def __float__(self):
+        return float(self.value)
+
+    # Support for indexing s[MutInt]
+    __index__ = __int__
+```
+
+
+
+[Back](ex2_4.md)