factor out mock python repl (#43)

langchain/python.py

@@ -0,0 +1,15 @@
+"""Mock Python REPL."""
+from typing import Dict, Optional
+
+
+class PythonREPL:
+    """Simulates a standalone Python REPL."""
+
+    def __init__(self, _globals: Optional[Dict] = None, _locals: Optional[Dict] = None):
+        """Initialize with optional globals and locals."""
+        self._globals = _globals if _globals is not None else {}
+        self._locals = _locals if _locals is not None else {}
+
+    def run(self, command: str) -> None:
+        """Run command with own globals/locals."""
+        exec(command, self._globals, self._locals)