change to python3 instead of explicit 3.6

ref/progress.py

@@ -0,0 +1,40 @@
+#!/usr/bin/env python
+
+import datetime
+import subprocess
+import time
+
+def waiter(seconds = 1):
+    prefix = ''
+    idx = 0
+    anims = ('|', '/', '-', '\\', 'O', '*', '\'', '^', '-', 'v', '_', '-')
+    max = len(anims) - 1
+    global is_done
+    print('Beginning dhparam gen...')
+    # This is just an example commant that takes a looong time.
+    c = subprocess.Popen(['openssl', 'dhparam', '-out', '/tmp/dhpem', '4096'],
+    #c = subprocess.Popen(['openssl', 'genrsa', '-out', '/tmp/dhpem', '4096'],
+                         stdout = subprocess.PIPE,
+                         stderr = subprocess.PIPE)
+    print('dhparam gen started.')
+    while c.poll() is None:
+        #print('.', end = '', flush = True)
+        try:
+            char = anims[idx]
+        except IndexError:
+            exit()
+        print('{0} => {1}'.format(prefix, char), end = '', flush = True)
+        idx = (idx + 1 if idx < max else 0)
+        prefix += '.'
+        if seconds:
+            time.sleep(seconds)
+        #print('\b', end = '')
+        print('\033[F')
+    with open('/tmp/dhpem.out', 'w') as f:
+        f.write(c.stdout.read().decode('utf-8'))
+        f.write(c.stderr.read().decode('utf-8'))
+    print('\nDone.')
+    is_done = True
+
+if __name__ == '__main__':
+    waiter(1)