BUG: Make polyder return a poly1d for the zeroeth order derivative when

the input is a poly1d. Fixes ticket #1249.

1 files changed, 9 insertions, 8 deletions

diff --git a/numpy/lib/polynomial.py b/numpy/lib/polynomial.py
index 66982186a..603655ec2 100644
--- a/numpy/lib/polynomial.py
+++ b/numpy/lib/polynomial.py
@@ -378,19 +378,20 @@ def polyder(p, m=1):
 
     """
     m = int(m)
+    if m < 0:
+        raise ValueError, "Order of derivative must be positive (see polyint)"
+
     truepoly = isinstance(p, poly1d)
     p = NX.asarray(p)
-    n = len(p)-1
+    n = len(p) - 1
     y = p[:-1] * NX.arange(n, 0, -1)
-    if m < 0:
-        raise ValueError, "Order of derivative must be positive (see polyint)"
     if m == 0:
-        return p
+        val = p
     else:
-        val = polyder(y, m-1)
-        if truepoly:
-            val = poly1d(val)
-        return val
+        val = polyder(y, m - 1)
+    if truepoly:
+        val = poly1d(val)
+    return val
 
 def polyfit(x, y, deg, rcond=None, full=False):
     """