move max_checkpoint from network to constants

electrum/constants.py

@@ -37,7 +37,14 @@ def read_json(filename, default):
     return r
 
 
-class BitcoinMainnet:
+class AbstractNet:
+
+    @classmethod
+    def max_checkpoint(cls) -> int:
+        return max(0, len(cls.CHECKPOINTS) * 2016 - 1)
+
+
+class BitcoinMainnet(AbstractNet):
 
     TESTNET = False
     WIF_PREFIX = 0x80
@@ -66,7 +73,7 @@ class BitcoinMainnet:
     BIP44_COIN_TYPE = 0
 
 
-class BitcoinTestnet:
+class BitcoinTestnet(AbstractNet):
 
     TESTNET = True
     WIF_PREFIX = 0xef