diff --git a/Demos/embed/assert_equal.py b/Demos/embed/assert_equal.py
index 34276e8d4a1..3f5bc34a8ff 100644
--- a/Demos/embed/assert_equal.py
+++ b/Demos/embed/assert_equal.py
@@ -1,12 +1,15 @@
+from __future__ import absolute_import, print_function
+
 import sys
+
 f1 = open(sys.argv[1])
 f2 = open(sys.argv[2])
 try:
     if f1.read() != f2.read():
-        print ("Files differ")
+        print("Files differ")
         sys.exit(1)
     else:
-        print ("Files identical")
+        print("Files identical")
 finally:
     f1.close()
     f2.close()
diff --git a/Demos/embed/embedded.pyx b/Demos/embed/embedded.pyx
index 85c15ae5b4d..edc5693d3ee 100644
--- a/Demos/embed/embedded.pyx
+++ b/Demos/embed/embedded.pyx
@@ -1,7 +1,8 @@
+# cython: language_level=3
 
-print __name__
+print(__name__)
 
 if __name__ == "__main__":
-    print "Hi, I'm embedded."
+    print("Hi, I'm embedded.")
 else:
-    print "I'm being imported."
+    print("I'm being imported.")
diff --git a/Demos/freeze/combinatorics.pyx b/Demos/freeze/combinatorics.pyx
index 752f3f0b101..1f5dc1e0ea5 100644
--- a/Demos/freeze/combinatorics.pyx
+++ b/Demos/freeze/combinatorics.pyx
@@ -1,9 +1,15 @@
+# cython: language_level=3
+
 import lcmath
 
+
 def nCr(n, r):
     """Return the number of ways to choose r elements of a set of n."""
-    return lcmath.exp( lcmath.lfactorial(n) - lcmath.lfactorial(r)
-                      - lcmath.lfactorial(n-r) )
+    return lcmath.exp(
+        lcmath.lfactorial(n) -
+        lcmath.lfactorial(r) -
+        lcmath.lfactorial(n-r)
+    )
 
 if __name__ == "__main__":
     import sys
@@ -11,4 +17,4 @@ if __name__ == "__main__":
         sys.stderr.write("USAGE: %s n r\nPrints n-choose-r.\n" % sys.argv[0])
         sys.exit(2)
     n, r = map(float, sys.argv[1:])
-    print nCr(n, r)
+    print(nCr(n, r))
diff --git a/Demos/freeze/lcmath.pyx b/Demos/freeze/lcmath.pyx
index f613dfe6eb0..2330d04ff4e 100644
--- a/Demos/freeze/lcmath.pyx
+++ b/Demos/freeze/lcmath.pyx
@@ -1,15 +1,20 @@
+# cython: language_level=3
+
 cdef extern from "math.h":
     double c_lgamma "lgamma" (double)
     double c_exp "exp" (double)
 
+
 def exp(n):
     """Return e**n."""
     return c_exp(n)
 
+
 def lfactorial(n):
     """Return an estimate of the log factorial of n."""
     return c_lgamma(n+1)
 
+
 def factorial(n):
     """Return an estimate of the factorial of n."""
     return c_exp( c_lgamma(n+1) )
@@ -21,4 +26,4 @@ if __name__ == "__main__":
         sys.stderr.write("USAGE: %s n\nPrints n!.\n" % sys.argv[0])
         sys.exit(2)
     n, = map(float, sys.argv[1:])
-    print factorial(n)
+    print(factorial(n))
diff --git a/Demos/integrate1.pyx b/Demos/integrate1.pyx
index b0dbc6f3196..eaa73d20a66 100644
--- a/Demos/integrate1.pyx
+++ b/Demos/integrate1.pyx
@@ -1,6 +1,9 @@
+# cython: language_level=3
+
 def f(x):
     return x**2-x
 
+
 def integrate_f(a, b, N):
     s = 0.0
     dx = (b-a)/N
diff --git a/Demos/integrate2.pyx b/Demos/integrate2.pyx
index e583fcb1929..9f8ccaa7ad1 100644
--- a/Demos/integrate2.pyx
+++ b/Demos/integrate2.pyx
@@ -1,6 +1,9 @@
+# cython: language_level=3
+
 cdef double f(double x) except? -2:
     return x**2-x
 
+
 def integrate_f(double a, double b, int N):
     cdef int i
     s = 0.0
diff --git a/Demos/integrate_timing.py b/Demos/integrate_timing.py
index 0e5776dd3a9..9148771f914 100644
--- a/Demos/integrate_timing.py
+++ b/Demos/integrate_timing.py
@@ -1,3 +1,5 @@
+from __future__ import absolute_import, print_function
+
 import timeit
 
 import integrate0, integrate1, integrate2
@@ -5,9 +7,9 @@
 number = 10
 py_time = None
 for m in ('integrate0', 'integrate1', 'integrate2'):
-    print m
+    print(m)
     t = min(timeit.repeat("integrate_f(0.0, 10.0, 10000000)", "from %s import integrate_f" % m, number=number))
     if py_time is None:
         py_time = t
-    print "    ", t / number, "s"
-    print "    ", py_time / t
+    print("    ", t / number, "s")
+    print("    ", py_time / t)
diff --git a/Demos/libraries/setup.py b/Demos/libraries/setup.py
index 01672a4751c..76b53630776 100644
--- a/Demos/libraries/setup.py
+++ b/Demos/libraries/setup.py
@@ -1,3 +1,5 @@
+from __future__ import absolute_import, print_function
+
 import os
 import sys
 
@@ -8,7 +10,7 @@
 
 # For demo purposes, we build our own tiny library.
 try:
-    print "building libmymath.a"
+    print("building libmymath.a")
     assert os.system("gcc -shared -fPIC -c mymath.c -o mymath.o") == 0
     assert os.system("ar rcs libmymath.a mymath.o") == 0
 except:
diff --git a/Demos/numpy_demo.pyx b/Demos/numpy_demo.pyx
index 914cd030c6e..59b5dc9ff28 100644
--- a/Demos/numpy_demo.pyx
+++ b/Demos/numpy_demo.pyx
@@ -1,7 +1,7 @@
-cimport numpy
-import numpy
+cimport numpy as cnp
 
-def sum_of_squares(numpy.ndarray[double, ndim=1] arr):
+
+def sum_of_squares(cnp.ndarray[double, ndim=1] arr):
     cdef long N = arr.shape[0]
     cdef double ss = 0
     for i in range(N):
diff --git a/Demos/overflow_perf.pyx b/Demos/overflow_perf.pyx
index d8dc2899025..1e4c2c20edf 100644
--- a/Demos/overflow_perf.pyx
+++ b/Demos/overflow_perf.pyx
@@ -1,6 +1,7 @@
+# cython: language_level=3
 # distutils: extra_compile_args = -O3
 
-import cython
+cimport cython
 
 ctypedef fused INT:
     int
@@ -15,6 +16,7 @@ ctypedef fused C_INT:
     unsigned int
     unsigned long long
 
+
 @cython.overflowcheck(False)
 def fib(INT n):
     """
@@ -54,12 +56,13 @@ def collatz(INT n):
     cdef INT k = 0
     while n != 1:
         if n % 2 == 0:
-            n /= 2
+            n //= 2
         else:
             n = 3*n + 1
         k += 1
     return int(k)
 
+
 @cython.overflowcheck(True)
 @cython.overflowcheck.fold(False)
 def collatz_overflow(INT n):
@@ -74,12 +77,13 @@ def collatz_overflow(INT n):
     cdef INT k = 0
     while n != 1:
         if n % 2 == 0:
-            n /= 2
+            n //= 2
         else:
             n = 3*n + 1
         k += 1
     return int(k)
 
+
 @cython.overflowcheck(True)
 @cython.overflowcheck.fold(True)
 def collatz_overflow_fold(INT n):
@@ -94,14 +98,13 @@ def collatz_overflow_fold(INT n):
     cdef INT k = 0
     while n != 1:
         if n % 2 == 0:
-            n /= 2
+            n //= 2
         else:
             n = 3*n + 1
         k += 1
     return int(k)
 
 
-
 @cython.overflowcheck(False)
 def factorial(INT n):
     """
@@ -129,7 +132,6 @@ def factorial_overflow(INT n):
     return int(res)
 
 
-
 @cython.overflowcheck(False)
 def most_orthogonal(C_INT[:,::1] vectors):
     cdef C_INT n = vectors.shape[0]
@@ -148,6 +150,7 @@ def most_orthogonal(C_INT[:,::1] vectors):
                 min_pair = i, j
     return vectors[i], vectors[j]
 
+
 @cython.overflowcheck(True)
 @cython.overflowcheck.fold(False)
 def most_orthogonal_overflow(C_INT[:,::1] vectors):
@@ -167,6 +170,7 @@ def most_orthogonal_overflow(C_INT[:,::1] vectors):
                 min_pair = i, j
     return vectors[i], vectors[j]
 
+
 @cython.overflowcheck(True)
 @cython.overflowcheck.fold(True)
 def most_orthogonal_overflow_fold(C_INT[:,::1] vectors):
diff --git a/Demos/overflow_perf_run.py b/Demos/overflow_perf_run.py
index ec84947c217..ce403695171 100644
--- a/Demos/overflow_perf_run.py
+++ b/Demos/overflow_perf_run.py
@@ -1,3 +1,5 @@
+from __future__ import absolute_import, print_function
+
 from overflow_perf import *
 
 import sys
@@ -11,7 +13,7 @@
 def run_tests(N):
     global f
     for func in most_orthogonal, fib, collatz, factorial:
-        print func.__name__
+        print(func.__name__)
         for type in ['int', 'unsigned int', 'long long', 'unsigned long long', 'object']:
             if func == most_orthogonal:
                 if type == 'object' or np == None:
@@ -23,15 +25,16 @@ def run_tests(N):
             else:
                 arg = N
             try:
-                print "%s[%s](%s)" % (func.__name__, type, N)
+                print("%s[%s](%s)" % (func.__name__, type, N))
                 with_overflow = my_timeit(globals()[func.__name__ + "_overflow"][type], arg)
                 no_overflow = my_timeit(func[type], arg)
-                print "\t%0.04e\t%0.04e\t%0.04f" % (no_overflow, with_overflow, with_overflow / no_overflow)
+                print("\t%0.04e\t%0.04e\t%0.04f" % (no_overflow, with_overflow, with_overflow / no_overflow))
                 if func.__name__ + "_overflow_fold" in globals():
                     with_overflow = my_timeit(globals()[func.__name__ + "_overflow_fold"][type], arg)
-                    print  "\t%0.04e\t%0.04e\t%0.04f" % (no_overflow, with_overflow, with_overflow / no_overflow), "(folded)"
+                    print("\t%0.04e\t%0.04e\t%0.04f (folded)" % (
+                        no_overflow, with_overflow, with_overflow / no_overflow))
             except OverflowError:
-                print "    ", "Overflow"
+                print("    ", "Overflow")
 
 def my_timeit(func, N):
     global f, arg
@@ -44,10 +47,11 @@ def my_timeit(func, N):
             break
     return res / times
 
+
 params = sys.argv[1:]
 if not params:
     params = [129, 9, 97]
 for arg in params:
-    print
-    print "N", arg
+    print()
+    print("N", arg)
     run_tests(int(arg))
diff --git a/Demos/primes.pyx b/Demos/primes.pyx
index c68b707a193..7f0c1279d81 100644
--- a/Demos/primes.pyx
+++ b/Demos/primes.pyx
@@ -1,4 +1,6 @@
-print "starting"
+# cython: language_level=3
+
+print("starting")
 
 def primes(int kmax):
     # cdef int n, k, i
@@ -10,11 +12,11 @@ def primes(int kmax):
     n = 2
     while k < kmax:
         i = 0
-        while i < k and n % p[i] <> 0:
-            i = i + 1
+        while i < k and n % p[i] != 0:
+            i += 1
         if i == k:
             p[k] = n
-            k = k + 1
+            k += 1
             result.append(n)
-        n = n + 1
+        n += 1
     return result
diff --git a/Demos/run_primes.py b/Demos/run_primes.py
index 487767d4228..656945ddbb8 100644
--- a/Demos/run_primes.py
+++ b/Demos/run_primes.py
@@ -1,7 +1,11 @@
+from __future__ import absolute_import, print_function
+
 import sys
 from primes import primes
+
 if len(sys.argv) >= 2:
     n = int(sys.argv[1])
 else:
     n = 1000
-print primes(n)
+
+print(primes(n))
diff --git a/Demos/run_spam.py b/Demos/run_spam.py
index e1c1e155442..41408bd14f9 100644
--- a/Demos/run_spam.py
+++ b/Demos/run_spam.py
@@ -1,8 +1,10 @@
+from __future__ import absolute_import, print_function
+
 from spam import Spam
 
 s = Spam()
-print "Created:", s
+print("Created:", s)
 s.set_amount(42)
-print "Amount =", s.get_amount()
+print("Amount =", s.get_amount())
 s.describe()
 s = None
diff --git a/Demos/spam.pyx b/Demos/spam.pyx
index 2992d0a456c..032d31a3401 100644
--- a/Demos/spam.pyx
+++ b/Demos/spam.pyx
@@ -1,3 +1,5 @@
+# cython: language_level=3
+
 #
 #  Example of an extension type.
 #
@@ -9,7 +11,7 @@ cdef class Spam:
     self.amount = 0
 
   def __dealloc__(self):
-    print self.amount, "tons of spam is history."
+    print(self.amount, "tons of spam is history.")
 
   def get_amount(self):
     return self.amount
@@ -18,4 +20,4 @@ cdef class Spam:
     self.amount = new_amount
 
   def describe(self):
-    print self.amount, "tons of spam!"
+    print(self.amount, "tons of spam!")