test: PSBT: eliminate magic numbers for global unsigned tx key (0)

Author: theStack

test/functional/test_framework/psbt.py

@@ -105,8 +105,8 @@ def __init__(self, *, g=None, i=None, o=None):
     def deserialize(self, f):
         assert f.read(5) == b"psbt\xff"
         self.g = from_binary(PSBTMap, f)
-        assert 0 in self.g.map
-        self.tx = from_binary(CTransaction, self.g.map[0])
+        assert PSBT_GLOBAL_UNSIGNED_TX in self.g.map
+        self.tx = from_binary(CTransaction, self.g.map[PSBT_GLOBAL_UNSIGNED_TX])
         self.i = [from_binary(PSBTMap, f) for _ in self.tx.vin]
         self.o = [from_binary(PSBTMap, f) for _ in self.tx.vout]
         return self
@@ -115,8 +115,8 @@ def serialize(self):
         assert isinstance(self.g, PSBTMap)
         assert isinstance(self.i, list) and all(isinstance(x, PSBTMap) for x in self.i)
         assert isinstance(self.o, list) and all(isinstance(x, PSBTMap) for x in self.o)
-        assert 0 in self.g.map
-        tx = from_binary(CTransaction, self.g.map[0])
+        assert PSBT_GLOBAL_UNSIGNED_TX in self.g.map
+        tx = from_binary(CTransaction, self.g.map[PSBT_GLOBAL_UNSIGNED_TX])
         assert len(tx.vin) == len(self.i)
         assert len(tx.vout) == len(self.o)
 
@@ -130,7 +130,7 @@ def make_blank(self):
         for m in self.i + self.o:
             m.map.clear()
 
-        self.g = PSBTMap(map={0: self.g.map[0]})
+        self.g = PSBTMap(map={PSBT_GLOBAL_UNSIGNED_TX: self.g.map[PSBT_GLOBAL_UNSIGNED_TX]})
 
     def to_base64(self):
         return base64.b64encode(self.serialize()).decode("utf8")