Be compatible with Python 3.9

birdvisu/maps_new/__init__.py

@@ -1,6 +1,6 @@
 from dataclasses import dataclass, field
 from abc import ABC, abstractmethod
-from typing import Sequence, Callable
+from typing import Sequence, Callable, Union
 
 # The topologies provided by TopologyProviders are independent and do not have
 # common routers, networks and links. We therefore join them on identifiers,
@@ -16,7 +16,7 @@ class Router:
 	# some separate part of code. But everything else takes data from a
 	# CombinedTopology object, so we would still need a way of resolving this,
 	# and adding a separate object would complicate the code even more.
-	details: tuple[str,list] | None = None
+	details: Union[tuple[str,list],None] = None
 	# source objects for this Router in case of combined topology. Key is some
 	# source identifier
 	# FIXME: This allows for different identifiers in sources, which should be
@@ -37,7 +37,7 @@ class Router:
 class Network:
 	ident: str
 	links: list['Link']
-	details: tuple[str,list] | None = None
+	details: Union[tuple[str,list],None] = None
 	sources: dict[str, 'Network'] = field(default_factory=dict)
 
 	@property