add support for python 3.9

src/kyber_py/polynomials/polynomials.py

@@ -1,3 +1,4 @@
+from ..utilities.utils import bit_count
 from .polynomials_generic import PolynomialRing, Polynomial
 
 
@@ -67,8 +68,8 @@ def cbd(self, input_bytes, eta, is_ntt=False):
         mask2 = (1 << 2 * eta) - 1
         for i in range(256):
             x = b_int & mask2
-            a = (x & mask).bit_count()
-            b = ((x >> eta) & mask).bit_count()
+            a = bit_count(x & mask)
+            b = bit_count((x >> eta) & mask)
             b_int >>= 2 * eta
             coefficients[i] = (a - b) % 3329
         return self(coefficients, is_ntt=is_ntt)

src/kyber_py/utilities/utils.py

@@ -1,3 +1,17 @@
+def bit_count(x):
+    """
+    Count the number of bits in x
+
+    Method to support old python as `x.bit_count()`
+    was released in Python 3.10 and we currently
+    support Python 3.9
+    """
+    try:
+        return x.bit_count()
+    except AttributeError:
+        return bin(x).count("1")
+
+
 def xor_bytes(a, b):
     """
     XOR two byte arrays, assume that they are