ch07

ch07/exceptions/trace.back.py

@@ -0,0 +1,25 @@
+# exceptions/trace.back.py
+def squareroot(number):
+    if number < 0:
+        raise ValueError("No negative numbers please")
+    return number ** .5
+
+def quadratic(a, b, c):
+    d = b ** 2 - 4 * a * c
+    return ((-b - squareroot(d)) / (2 * a),
+            (-b + squareroot(d)) / (2 * a))
+
+quadratic(1, 0, 1)  # x**2 + 1 == 0
+
+
+"""
+$ python exceptions/trace.back.py
+Traceback (most recent call last):
+  File "exceptions/trace.back.py", line 12, in <module>
+    quadratic(1, 0, 1)  # x**2 + 1 == 0
+  File "exceptions/trace.back.py", line 9, in quadratic
+    return ((-b - squareroot(d)) / (2 * a),
+  File "exceptions/trace.back.py", line 4, in squareroot
+    raise ValueError("No negative numbers please")
+ValueError: No negative numbers please
+"""