Adding chapter 4 source code

chapter4/errors/exception4.py

@@ -0,0 +1,28 @@
+#exception3.py
+import math
+
+class NumTypeError(TypeError):
+    pass
+
+class NegativeNumError(Exception):
+    def __init__(self):
+        super().__init__("Negative number not supported")
+
+def sqrt(num):
+
+    if not isinstance(num, (int, float)) :
+        raise NumTypeError("only numbers are allowed")
+    if num < 0:
+        raise NegativeNumError
+
+    return math.sqrt(num)
+
+if __name__ == "__main__":
+    try:
+        print(sqrt(9))
+        print(sqrt('a'))
+        print (sqrt(-9))
+    except NumTypeError as e:
+        print(e)
+    except NegativeNumError as e:
+        print(e)