Provide more contextual error message for PyCoder

sdks/python/apache_beam/coders/coder_impl.py

@@ -1014,7 +1014,13 @@ class VarIntCoderImpl(StreamCoderImpl):
   A coder for int objects."""
   def encode_to_stream(self, value, out, nested):
     # type: (int, create_OutputStream, bool) -> None
-    out.write_var_int64(value)
+    try:
+      out.write_var_int64(value)
+    except OverflowError as e:
+      raise OverflowError(
+          f"Integer value '{value}' is out of the encodable range for VarIntCoder. "
+          f"This coder is limited to values that fit within a 64-bit signed integer "
+          f"(-(2**63) to 2**63 - 1). Original error: {e}") from e
 
   def decode_from_stream(self, in_stream, nested):
     # type: (create_InputStream, bool) -> int
@@ -1036,7 +1042,13 @@ def decode(self, encoded):
   def estimate_size(self, value, nested=False):
     # type: (Any, bool) -> int
     # Note that VarInts are encoded the same way regardless of nesting.
-    return get_varint_size(value)
+    try:
+      return get_varint_size(value)
+    except OverflowError as e:
+      raise OverflowError(
+          f"Cannot estimate size for integer value '{value}'. "
+          f"Value is out of the range for VarIntCoder (64-bit signed integer). "
+          f"Original error: {e}") from e
 
 
 class VarInt32CoderImpl(StreamCoderImpl):