require >= Python 3.7

This means that Ubuntu Bionic (Python 3.6.9) is no longer supported

mmgen/main_addrimport.py

@@ -118,7 +118,7 @@ def check_opts(tw):
 
 async def import_addr(tw,addr,label,rescan,msg_fmt,msg_args):
 	try:
-		task = asyncio.ensure_future(tw.import_address(addr,label,rescan)) # Python 3.7+: create_task()
+		task = asyncio.create_task(tw.import_address(addr,label,rescan))
 		if rescan:
 			start = time.time()
 			while True:

mmgen/util.py

@@ -927,5 +927,4 @@ def run_session(callback,backend=None):
 		else:
 			return await callback
 
-	# return asyncio.run(do()) # Python 3.7+
-	return asyncio.get_event_loop().run_until_complete(do())
+	return asyncio.run(do())

setup.py

@@ -21,11 +21,11 @@ from subprocess import run,PIPE
 from shutil import copy2
 
 sys_ver = sys.version_info[:2]
-req_ver = (3,6)
+req_ver = (3,7)
 ver2f = lambda t: float('{}.{:03}'.format(*t))
 
 if ver2f(sys_ver) < ver2f(req_ver):
-	m = '{}.{}: incorrect Python version.  MMGen requires Python {}.{} or greater\n'
+	m = '{}.{}: unsupported Python version.  MMGen requires Python {}.{} or greater\n'
 	sys.stderr.write(m.format(*sys_ver,*req_ver))
 	sys.exit(1)