1 files changed, 28 insertions, 0 deletions
diff --git a/ptpython/lexer.py b/ptpython/lexer.py
new file mode 100644
index 0000000..62e470f
--- /dev/null
+++ b/ptpython/lexer.py
@@ -0,0 +1,28 @@
+from typing import Callable, Optional
+
+from prompt_toolkit.document import Document
+from prompt_toolkit.formatted_text import StyleAndTextTuples
+from prompt_toolkit.lexers import Lexer, PygmentsLexer
+from pygments.lexers import BashLexer
+from pygments.lexers import Python3Lexer as PythonLexer
+
+__all__ = ["PtpythonLexer"]
+
+
+class PtpythonLexer(Lexer):
+    """
+    Lexer for ptpython input.
+
+    If the input starts with an exclamation mark, use a Bash lexer, otherwise,
+    use a Python 3 lexer.
+    """
+
+    def __init__(self, python_lexer: Optional[Lexer] = None) -> None:
+        self.python_lexer = python_lexer or PygmentsLexer(PythonLexer)
+        self.system_lexer = PygmentsLexer(BashLexer)
+
+    def lex_document(self, document: Document) -> Callable[[int], StyleAndTextTuples]:
+        if document.text.startswith("!"):
+            return self.system_lexer.lex_document(document)
+
+        return self.python_lexer.lex_document(document)