1 files changed, 57 insertions, 0 deletions
diff --git a/ptpython/validator.py b/ptpython/validator.py
new file mode 100644
index 0000000..0f6a4ea
--- /dev/null
+++ b/ptpython/validator.py
@@ -0,0 +1,57 @@
+from prompt_toolkit.validation import ValidationError, Validator
+
+from .utils import unindent_code
+
+__all__ = ["PythonValidator"]
+
+
+class PythonValidator(Validator):
+    """
+    Validation of Python input.
+
+    :param get_compiler_flags: Callable that returns the currently
+        active compiler flags.
+    """
+
+    def __init__(self, get_compiler_flags=None):
+        self.get_compiler_flags = get_compiler_flags
+
+    def validate(self, document):
+        """
+        Check input for Python syntax errors.
+        """
+        text = unindent_code(document.text)
+
+        # When the input starts with Ctrl-Z, always accept. This means EOF in a
+        # Python REPL.
+        if text.startswith("\x1a"):
+            return
+
+        # When the input starts with an exclamation mark. Accept as shell
+        # command.
+        if text.lstrip().startswith("!"):
+            return
+
+        try:
+            if self.get_compiler_flags:
+                flags = self.get_compiler_flags()
+            else:
+                flags = 0
+
+            compile(text, "<input>", "exec", flags=flags, dont_inherit=True)
+        except SyntaxError as e:
+            # Note, the 'or 1' for offset is required because Python 2.7
+            # gives `None` as offset in case of '4=4' as input. (Looks like
+            # fixed in Python 3.)
+            # TODO: This is not correct if indentation was removed.
+            index = document.translate_row_col_to_index(
+                e.lineno - 1, (e.offset or 1) - 1
+            )
+            raise ValidationError(index, f"Syntax Error: {e}")
+        except TypeError as e:
+            # e.g. "compile() expected string without null bytes"
+            raise ValidationError(0, str(e))
+        except ValueError as e:
+            # In Python 2, compiling "\x9" (an invalid escape sequence) raises
+            # ValueError instead of SyntaxError.
+            raise ValidationError(0, "Syntax Error: %s" % e)