Print out commercial software notification on import

README.md

@@ -18,5 +18,8 @@ Values are always applied to the logic in timestamp (not arrival) order.
 
 ## License
 
-bytewax-interval is commercially licensed with publicly available source code.
-Please see the full details in [LICENSE](./LICENSE.md).
+`bytewax-interval` is commercially licensed with publicly available
+source code. You are welcome to prototype using this module for free,
+but any use on business data requires a paid license. See
+https://modules.bytewax.io/ for a license. Please see the full details
+in [LICENSE](./LICENSE.md).

src/bytewax/interval/__init__.py

@@ -1,6 +1,8 @@
 """Time-based interval operators."""
 
 import copy
+import os
+import sys
 from abc import ABC, abstractmethod
 from dataclasses import dataclass, field
 from datetime import datetime, timedelta
@@ -43,6 +45,18 @@
 )
 from typing_extensions import TypeAlias, overload, override
 
+if "BYTEWAX_LICENSE" not in os.environ:
+    msg = (
+        "`bytewax-interval` is commercially licensed "
+        "with publicly available source code.\n"
+        "You are welcome to prototype using this module for free, "
+        "but any use on business data requires a paid license.\n"
+        "See https://modules.bytewax.io/ for a license. "
+        "Set the env var `BYTEWAX_LICENSE=1` to suppress this message."
+    )
+    print(msg, file=sys.stderr)
+
+
 LeftRight: TypeAlias = Literal["left", "right"]
 """Which side did a value come from."""