self.log prints to stderr.

main.py

@@ -35,6 +35,7 @@
   ./main.py to-cold $TXID
 
 """
+import sys
 import struct
 import hashlib
 import sys
@@ -79,6 +80,10 @@
 BLANK_INPUT = CMutableTxIn
 
 
+def no_output(*args, **kwargs):
+    print(*args, file=sys.stderr, **kwargs)
+
+
 @dataclass(frozen=True)
 class Coin:
     outpoint: COutPoint
@@ -104,6 +109,8 @@ class Wallet:
     coins: t.List[Coin]
     network: str
 
+    log: t.Callable = no_output
+
     @classmethod
     def generate(cls, seed: bytes, network: str = "regtest") -> "Wallet":
         return cls(
@@ -455,10 +462,6 @@ def t_(b: t.Union[bytes, t.Any]) -> str:
 bold = make_color(esc(1), esc(22))
 
 
-def no_output(*args, **kwargs):
-    pass
-
-
 @dataclass
 class VaultExecutor:
     plan: VaultPlan