examples: add sign message python example

Require Python3 and eth_keys

Signed-off-by: Clément Péron <peron.clem@gmail.com>

examples/ethBase.py

@@ -23,14 +23,12 @@ from rlp import Serializable
 
 try:
     from Crypto.Hash import keccak
-
-    def sha3_256(x): return keccak.new(digest_bits=256, data=x).digest()
+    def sha3_256(x): return keccak.new(digest_bits=256, data=x.encode()).digest()
 except:
     import sha3 as _sha3
-
     def sha3_256(x): return _sha3.sha3_256(x).digest()
-address = Binary.fixed_length(20, allow_empty=True)
 
+address = Binary.fixed_length(20, allow_empty=True)
 
 def sha3(seed):
     return sha3_256(str(seed))
@@ -71,4 +69,4 @@ def unsigned_tx_from_tx(tx):
         to=tx.to,
         value=tx.value,
         data=tx.data,
-    )
+    )