diff --git a/smart_open/s3.py b/smart_open/s3.py
index 8c2b3c2f..95138538 100644
--- a/smart_open/s3.py
+++ b/smart_open/s3.py
@@ -352,6 +352,11 @@ class SeekableBufferedInputBase(BufferedInputBase):
 
     def __init__(self, bucket, key, version_id=None, buffer_size=DEFAULT_BUFFER_SIZE,
                  line_terminator=BINARY_NEWLINE, session=None, resource_kwargs=None):
+
+        self._buffer_size = buffer_size
+        self._session = session
+        self._resource_kwargs = resource_kwargs
+
         if session is None:
             session = boto3.Session()
         if resource_kwargs is None:
@@ -412,6 +417,29 @@ def truncate(self, size=None):
         """Unsupported."""
         raise io.UnsupportedOperation
 
+    def __str__(self):
+        return "smart_open.s3.SeekableBufferedInputBase(%r, %r)" % (self._object.bucket_name, self._object.key)
+
+    def __repr__(self):
+        return (
+            "smart_open.s3.SeekableBufferedInputBase("
+            "bucket=%r, "
+            "key=%r, "
+            "version_id=%r, "
+            "buffer_size=%r, "
+            "line_terminator=%r, "
+            "session=%r, "
+            "resource_kwargs=%r)"
+        ) % (
+            self._object.bucket_name,
+            self._object.key,
+            self._version_id,
+            self._buffer_size,
+            self._line_terminator,
+            self._session,
+            self._resource_kwargs,
+        )
+
 
 class BufferedOutputBase(io.BufferedIOBase):
     """Writes bytes to S3.
@@ -427,6 +455,11 @@ def __init__(
             resource_kwargs=None,
             multipart_upload_kwargs=None,
             ):
+
+        self._session = session
+        self._resource_kwargs = resource_kwargs
+        self._multipart_upload_kwargs = multipart_upload_kwargs
+
         if min_part_size < MIN_MIN_PART_SIZE:
             logger.warning("S3 requires minimum part size >= 5MB; \
 multipart upload may fail")
@@ -451,6 +484,7 @@ def __init__(
         self._total_parts = 0
         self._parts = []
 
+
         #
         # This member is part of the io.BufferedIOBase interface.
         #
@@ -553,6 +587,27 @@ def __exit__(self, exc_type, exc_val, exc_tb):
         else:
             self.close()
 
+    def __str__(self):
+        return "smart_open.s3.BufferedOutputBase(%r, %r)" % (self._object.bucket_name, self._object.key)
+
+    def __repr__(self):
+        return (
+            "smart_open.s3.BufferedOutputBase("
+            "bucket=%r, "
+            "key=%r, "
+            "min_part_size=%r, "
+            "session=%r, "
+            "resource_kwargs=%r, "
+            "multipart_upload_kwargs=%r)"
+        ) % (
+            self._object.bucket_name,
+            self._object.key,
+            self._min_part_size,
+            self._session,
+            self._resource_kwargs,
+            self._multipart_upload_kwargs,
+        )
+
 
 def iter_bucket(bucket_name, prefix='', accept_key=None,
                 key_limit=None, workers=16, retries=3):