Closes #9574: Note that complex constructor doesn't allow whitespace around central operator.
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index 5f7bf4d..f9e5e1b 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -247,6 +247,13 @@
the function serves as a numeric conversion function like :func:`int`,
:func:`long` and :func:`float`. If both arguments are omitted, returns ``0j``.
+ .. note::
+
+ When converting from a string, the string must not contain whitespace
+ around the central ``+`` or ``-`` operator. For example,
+ ``complex('1+2j')`` is fine, but ``complex('1 + 2j')`` raises
+ :exc:`ValueError`.
+
The complex type is described in :ref:`typesnumeric`.