SF bug [ #409448 ] Complex division is braindead

http://sourceforge.net/tracker/?func=detail&aid=409448&group_id=5470&atid=105470
Now less braindead.  Also added test_complex.py, which doesn't test much, but
fails without this patch.

1 files changed, 65 insertions, 0 deletions

diff --git a/Lib/test/test_complex.py b/Lib/test/test_complex.py
new file mode 100644
index 0000000..ef44fbc
--- /dev/null
+++ b/Lib/test/test_complex.py
@@ -0,0 +1,65 @@
+from test_support import TestFailed
+from random import random
+
+# XXX need many, many more tests here.
+
+nerrors = 0
+
+def check_close_real(x, y, eps=1e-12):
+    """Return true iff floats x and y "are close\""""
+    # put the one with larger magnitude second
+    if abs(x) > abs(y):
+        x, y = y, x
+    if y == 0:
+        return abs(x) < eps
+    if x == 0:
+        return abs(y) < eps
+    # check that relative difference < eps
+    return abs((x-y)/y) < eps
+
+def check_close(x, y, eps=1e-12):
+    """Return true iff complexes x and y "are close\""""
+    return check_close_real(x.real, y.real, eps) and \
+           check_close_real(x.imag, y.imag, eps)
+
+def test_div(x, y):
+    """Compute complex z=x*y, and check that z/x==y and z/y==x."""
+    global nerrors
+    z = x * y
+    if x != 0:
+        q = z / x
+        if not check_close(q, y):
+            nerrors += 1
+            print `z`, "/", `x`, "==", `q`, "but expected", `y`
+    if y != 0:
+        q = z / y
+        if not check_close(q, x):
+            nerrors += 1
+            print `z`, "/", `y`, "==", `q`, "but expected", `x`
+
+simple_real = [float(i) for i in range(-5, 6)]
+simple_complex = [complex(x, y) for x in simple_real for y in simple_real]
+for x in simple_complex:
+    for y in simple_complex:
+        test_div(x, y)
+
+# A naive complex division algorithm (such as in 2.0) is very prone to
+# nonsense errors for these (overflows and underflows).
+test_div(complex(1e200, 1e200), 1+0j)
+test_div(complex(1e-200, 1e-200), 1+0j)
+
+# Just for fun.
+for i in range(100):
+    test_div(complex(random(), random()),
+             complex(random(), random()))
+
+try:
+    z = 1.0 / (0+0j)
+except ZeroDivisionError:
+    pass
+else:
+    nerrors += 1
+    raise TestFailed("Division by complex 0 didn't raise ZeroDivisionError")
+
+if nerrors:
+    raise TestFailed("%d tests failed" % nerrors)