fix StringIO constructor docs #5452
diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index cfd1af5..6ce28d0 100644
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -637,13 +637,13 @@
Whether line buffering is enabled.
-.. class:: StringIO([initial_value[, encoding[, errors[, newline]]]])
+.. class:: StringIO([initial_value[, newline]])
An in-memory stream for text. It inherits :class:`TextIOWrapper`.
- Create a new StringIO stream with an initial value, encoding, error handling,
- and newline setting. See :class:`TextIOWrapper`\'s constructor for more
- information.
+ The initial value of the buffer (an empty string by default) can be set by
+ providing *initial_value*. The *newline* argument works like that of
+ :class:`TextIOWrapper`. The default is to do no newline translation.
:class:`StringIO` provides this method in addition to those from
:class:`TextIOWrapper` and its parents: