diff --git a/IPython/core/inputsplitter.py b/IPython/core/inputsplitter.py
index 84aa0a7..0256278 100644
--- a/IPython/core/inputsplitter.py
+++ b/IPython/core/inputsplitter.py
@@ -386,7 +386,7 @@ class InputSplitter(object):
         finally:
             self.reset()
 
-    def push(self, lines):
+    def push(self, lines:str) -> bool:
         """Push one or more lines of input.
 
         This stores the given lines and returns a status code indicating
@@ -408,6 +408,7 @@ class InputSplitter(object):
           this value is also stored as a private attribute (``_is_complete``), so it
           can be queried at any time.
         """
+        assert isinstance(lines, str)
         self._store(lines)
         source = self.source
 
@@ -677,7 +678,7 @@ class IPythonInputSplitter(InputSplitter):
         finally:
             self.reset()
 
-    def push(self, lines):
+    def push(self, lines:str) -> bool:
         """Push one or more lines of IPython input.
 
         This stores the given lines and returns a status code indicating
@@ -700,9 +701,8 @@ class IPythonInputSplitter(InputSplitter):
           this value is also stored as a private attribute (_is_complete), so it
           can be queried at any time.
         """
-
+        assert isinstance(lines, str)
         # We must ensure all input is pure unicode
-        lines = cast_unicode(lines, self.encoding)
         # ''.splitlines() --> [], but we need to push the empty line to transformers
         lines_list = lines.splitlines()
         if not lines_list:
diff --git a/IPython/utils/text.py b/IPython/utils/text.py
index e844203..14405ed 100644
--- a/IPython/utils/text.py
+++ b/IPython/utils/text.py
@@ -538,7 +538,7 @@ class FullEvalFormatter(Formatter):
     """
     # copied from Formatter._vformat with minor changes to allow eval
     # and replace the format_spec code with slicing
-    def vformat(self, format_string, args, kwargs):
+    def vformat(self, format_string:str, args, kwargs)->str:
         result = []
         for literal_text, field_name, format_spec, conversion in \
                 self.parse(format_string):
@@ -566,7 +566,7 @@ class FullEvalFormatter(Formatter):
                 # format the object and append to the result
                 result.append(self.format_field(obj, ''))
 
-        return ''.join(py3compat.cast_unicode(s) for s in result)
+        return ''.join(result)
 
 
 class DollarFormatter(FullEvalFormatter):