Merge pull request #93 from python-cmd2/gnureadline

cmd2 now protects against GNU Readline bug when ANSI escapes in prompt

Author: tleonhardt

cmd2.py

@@ -62,15 +62,6 @@
 # noinspection PyUnresolvedReferences
 from six.moves.urllib.request import urlopen
 
-# Prefer statically linked gnureadline if available (for Mac OS X compatibility due to issues with libedit)
-try:
-    import gnureadline as readline
-except ImportError:
-    try:
-        import readline
-    except ImportError:
-        pass
-
 # Python 3 compatibility hack due to no built-in file keyword in Python 3
 # Due to one occurrence of isinstance(<foo>, file) checking to see if something is of file type
 try:
@@ -88,6 +79,13 @@
 except ImportError:
     ipython_available = False
 
+# Try to import readline, but allow failure for convenience in Windows unit testing
+# Note: If this actually fails, you should install readline on Linux or Mac or pyreadline on Windows
+try:
+    import readline
+except ImportError:
+    pass
+
 __version__ = '0.7.1a'
 
 # Pyparsing enablePackrat() can greatly speed up parsing, but problems have been seen in Python 3 in the past
@@ -1105,12 +1103,41 @@ def _default(self, statement):
 
         return False
 
+    @staticmethod
+    def _surround_ansi_escapes(prompt, start="\x01", end="\x02"):
+        """Overcome bug in GNU Readline in relation to calculation of prompt length in presence of ASNI escape codes.
+
+        :param prompt: str - original prompt
+        :param start: str - start code to tell GNU Readline about beginning of invisible characters
+        :param end: str - end code to tell GNU Readline about end of invisible characters
+        :return: str - prompt safe to pass to GNU Readline
+        """
+        # Windows terminals don't use ANSI escape codes and Windows readline isn't based on GNU Readline
+        if sys.platform == "win32":
+            return prompt
+
+        escaped = False
+        result = ""
+
+        for c in prompt:
+            if c == "\x1b" and not escaped:
+                result += start + c
+                escaped = True
+            elif c.isalpha() and escaped:
+                result += c + end
+                escaped = False
+            else:
+                result += c
+
+        return result
+
     def pseudo_raw_input(self, prompt):
         """copied from cmd's cmdloop; like raw_input, but accounts for changed stdin, stdout"""
 
         if self.use_rawinput:
+            safe_prompt = self._surround_ansi_escapes(prompt)
             try:
-                line = sm.input(prompt)
+                line = sm.input(safe_prompt)
             except EOFError:
                 line = 'EOF'
         else:

docs/index.rst

@@ -35,7 +35,7 @@ The basic use of ``cmd2`` is identical to that of cmd_.
 
    The tab-completion feature provided by cmd_ relies on underlying capability provided by GNU readline or an
    equivalent library.  Linux distros will almost always come with the required library installed.
-   For Mac OS X, we recommend installing the `gnureadline <https://pypi.python.org/pypi/gnureadline>`_ Python module.
+   For Mac OS X, we recommend using the `Homebrew <https://brew.sh>`_ package manager to install the ``readline`` package.
    For Windows, we recommend installing the `pyreadline <https://pypi.python.org/pypi/pyreadline>`_ Python module.
 
 Resources