"import braces" crashes ipython

[sousaw]

Trying to trigger the well-known easter egg "not a chance" with "from future import braces" results in IPython 0.11 crashing as detailed in the crash log below. I realize this is not a very serious bug but I still thought it might be interesting for the developers.

IPython post-mortem report

{'commit_hash': '464280a',
 'commit_source': 'archive substitution',
 'ipython_path': '/usr/lib/python2.7/dist-packages/IPython',
 'ipython_version': '0.11',
 'os_name': 'posix',
 'platform': 'Linux-3.0.0-1-amd64-x86_64-with-debian-wheezy-sid',
 'sys_executable': '/usr/bin/python',
 'sys_platform': 'linux2',
 'sys_version': '2.7.2+ (default, Oct  5 2011, 10:41:47) \n[GCC 4.6.1]'}

***************************************************************************



***************************************************************************

Crash traceback:

---------------------------------------------------------------------------
SyntaxError                                  Python 2.7.2+: /usr/bin/python
                                                   Fri Oct  7 19:02:37 2011
A problem occured executing Python code.  Here is the sequence of function
calls leading up to the error, with the most recent (innermost) call last.
/usr/bin/ipython in <module>()
      1 #!/usr/bin/env python
      2 """Terminal-based IPython entry point.
      3 """
      4 
      5 from IPython.frontend.terminal.ipapp import launch_new_instance
      6 
      7 try:
----> 8   launch_new_instance()
        global launch_new_instance = <function launch_new_instance at 0x160fe60>
      9 except ImportError as e:
     10   if "qt.console.qtconsoleapp" in e.message:
     11     print "Could not start qtconsole. Please install ipython-qtconsole"

/usr/lib/python2.7/dist-packages/IPython/frontend/terminal/ipapp.pyc in launch_new_instance()
    355         ipython_dir = get_ipython_dir()
    356     profile_dir = os.path.join(ipython_dir, 'profile_default')
    357     cl = PyFileConfigLoader(default_config_file_name, profile_dir)
    358     try:
    359         config = cl.load_config()
    360     except IOError:
    361         # no config found
    362         config = Config()
    363     return config
    364 
    365 
    366 def launch_new_instance():
    367     """Create and run a full blown IPython instance"""
    368     app = TerminalIPythonApp.instance()
    369     app.initialize()
--> 370     app.start()
    371 
    372 
    373 if __name__ == '__main__':
    374     launch_new_instance()

/usr/lib/python2.7/dist-packages/IPython/frontend/terminal/ipapp.pyc in start(self=<IPython.frontend.terminal.ipapp.TerminalIPythonApp object>)
    329         if gui or self.pylab:
    330             try:
    331                 self.log.info("Enabling GUI event loop integration, "
    332                               "toolkit=%s, pylab=%s" % (gui, self.pylab) )
    333                 activate(gui)
    334             except:
    335                 self.log.warn("Error in enabling GUI event loop integration:")
    336                 self.shell.showtraceback()
    337 
    338     def start(self):
    339         if self.subapp is not None:
    340             return self.subapp.start()
    341         # perform any prexec steps:
    342         if self.interact:
    343             self.log.debug("Starting IPython's mainloop...")
--> 344             self.shell.mainloop()
    345         else:
    346             self.log.debug("IPython not interactive...")
    347 
    348 
    349 def load_default_config(ipython_dir=None):
    350     """Load the default config file from the default ipython_dir.
    351 
    352     This is useful for embedded shells.
    353     """
    354     if ipython_dir is None:
    355         ipython_dir = get_ipython_dir()
    356     profile_dir = os.path.join(ipython_dir, 'profile_default')
    357     cl = PyFileConfigLoader(default_config_file_name, profile_dir)
    358     try:
    359         config = cl.load_config()

/usr/lib/python2.7/dist-packages/IPython/frontend/terminal/interactiveshell.pyc in mainloop(self=<IPython.frontend.terminal.interactiveshell.TerminalInteractiveShell object>, display_banner=None)
    207     #-------------------------------------------------------------------------
    208     # Mainloop and code execution logic
    209     #-------------------------------------------------------------------------
    210 
    211     def mainloop(self, display_banner=None):
    212         """Start the mainloop.
    213 
    214         If an optional banner argument is given, it will override the
    215         internally created default banner.
    216         """
    217         
    218         with nested(self.builtin_trap, self.display_trap):
    219 
    220             while 1:
    221                 try:
--> 222                     self.interact(display_banner=display_banner)
        global See = undefined
        global also = undefined
    223                     #self.interact_with_readline()                
    224                     # XXX for testing of a readline-decoupled repl loop, call
    225                     # interact_with_readline above
    226                     break
    227                 except KeyboardInterrupt:
    228                     # this should not be necessary, but KeyboardInterrupt
    229                     # handling seems rather unpredictable...
    230                     self.write("\nKeyboardInterrupt in interact()\n")
    231 
    232     def interact(self, display_banner=None):
    233         """Closely emulate the interactive Python console."""
    234 
    235         # batch run -> do not interact        
    236         if self.exit_now:
    237             return

/usr/lib/python2.7/dist-packages/IPython/frontend/terminal/interactiveshell.pyc in interact(self=<IPython.frontend.terminal.interactiveshell.TerminalInteractiveShell object>, display_banner=False)
    297                      'Because of how pdb handles the stack, it is impossible\n'
    298                      'for IPython to properly format this particular exception.\n'
    299                      'IPython will resume normal operation.')
    300             except:
    301                 # exceptions here are VERY RARE, but they can be triggered
    302                 # asynchronously by signal handlers, for example.
    303                 self.showtraceback()
    304             else:
    305                 self.input_splitter.push(line)
    306                 more = self.input_splitter.push_accepts_more()
    307                 if (self.SyntaxTB.last_syntax_error and
    308                     self.autoedit_syntax):
    309                     self.edit_syntax_error()
    310                 if not more:
    311                     source_raw = self.input_splitter.source_raw_reset()[1]
--> 312                     self.run_cell(source_raw)
    313                 
    314         # We are off again...
    315         __builtin__.__dict__['__IPYTHON__active'] -= 1
    316 
    317         # Turn off the exit flag, so the mainloop can be restarted if desired
    318         self.exit_now = False
    319 
    320     def raw_input(self, prompt=''):
    321         """Write a prompt and read a line.
    322 
    323         The returned line does not include the trailing newline.
    324         When the user enters the EOF key sequence, EOFError is raised.
    325 
    326         Optional inputs:
    327 

/usr/lib/python2.7/dist-packages/IPython/core/interactiveshell.pyc in run_cell(self=<IPython.frontend.terminal.interactiveshell.TerminalInteractiveShell object>, raw_cell=u'from __future__ import braces\n', store_history=True)
   2282             
   2283                 with self.display_trap:
   2284                     try:
   2285                         code_ast = ast.parse(cell, filename=cell_name)
   2286                     except IndentationError:
   2287                         self.showindentationerror()
   2288                         self.execution_count += 1
   2289                         return None
   2290                     except (OverflowError, SyntaxError, ValueError, TypeError,
   2291                             MemoryError):
   2292                         self.showsyntaxerror()
   2293                         self.execution_count += 1
   2294                         return None
   2295             
   2296                     self.run_ast_nodes(code_ast.body, cell_name,
-> 2297                                                         interactivity="last_expr")
   2298             
   2299                     # Execute any registered post-execution functions.
   2300                     for func, status in self._post_execute.iteritems():
   2301                         if not status:
   2302                             continue
   2303                         try:
   2304                             func()
   2305                         except:
   2306                             self.showtraceback()
   2307                             # Deactivate failing function
   2308                             self._post_execute[func] = False
   2309                 
   2310         if store_history:
   2311             # Write output to the database. Does nothing unless
   2312             # history output logging is enabled.

/usr/lib/python2.7/dist-packages/IPython/core/interactiveshell.pyc in run_ast_nodes(self=<IPython.frontend.terminal.interactiveshell.TerminalInteractiveShell object>, nodelist=[<_ast.ImportFrom object>], cell_name='<ipython-input-1-2aebb3fc8ecf>', interactivity='none')
   2342                 interactivity = "none"
   2343         
   2344         if interactivity == 'none':
   2345             to_run_exec, to_run_interactive = nodelist, []
   2346         elif interactivity == 'last':
   2347             to_run_exec, to_run_interactive = nodelist[:-1], nodelist[-1:]
   2348         elif interactivity == 'all':
   2349             to_run_exec, to_run_interactive = [], nodelist
   2350         else:
   2351             raise ValueError("Interactivity was %r" % interactivity)
   2352             
   2353         exec_count = self.execution_count
   2354         
   2355         for i, node in enumerate(to_run_exec):
   2356             mod = ast.Module([node])
-> 2357             code = self.compile(mod, cell_name, "exec")
   2358             if self.run_code(code):
   2359                 return True
   2360 
   2361         for i, node in enumerate(to_run_interactive):
   2362             mod = ast.Interactive([node])
   2363             code = self.compile(mod, cell_name, "single")
   2364             if self.run_code(code):
   2365                 return True
   2366 
   2367         return False
   2368     
   2369     def run_code(self, code_obj):
   2370         """Execute a code object.
   2371 
   2372         When an exception occurs, self.showtraceback() is called to display a

/usr/lib/python2.7/codeop.pyc in __call__(self=<IPython.core.compilerop.CachingCompiler instance>, source=<_ast.Module object>, filename='<ipython-input-1-2aebb3fc8ecf>', symbol='exec')
    118     - Raise SyntaxError, ValueError or OverflowError if the command is a
    119       syntax error (OverflowError and ValueError can be produced by
    120       malformed literals).
    121     """
    122     return _maybe_compile(_compile, source, filename, symbol)
    123 
    124 class Compile:
    125     """Instances of this class behave much like the built-in compile
    126     function, but if one is used to compile text containing a future
    127     statement, it "remembers" and compiles all subsequent program texts
    128     with the statement in force."""
    129     def __init__(self):
    130         self.flags = PyCF_DONT_IMPLY_DEDENT
    131 
    132     def __call__(self, source, filename, symbol):
--> 133         codeob = compile(source, filename, symbol, self.flags, 1)
    134         for feature in _features:
    135             if codeob.co_flags & feature.compiler_flag:
    136                 self.flags |= feature.compiler_flag
    137         return codeob
    138 
    139 class CommandCompiler:
    140     """Instances of this class have __call__ methods identical in
    141     signature to compile_command; the difference is that if the
    142     instance compiles program text containing a __future__ statement,
    143     the instance 'remembers' and compiles all subsequent program texts
    144     with the statement in force."""
    145 
    146     def __init__(self,):
    147         self.compiler = Compile()
    148 

SyntaxError: not a chance (<ipython-input-1-2aebb3fc8ecf>, line 1)

***************************************************************************

History of session input:from __future__ import braces
*** Last line of input (may not be in above history):
from __future__ import braces

[fperez]

Thanks for your report! I can confirm the problem existed on 0.11, but fortunately it's already fixed on trunk, so you can either update to running from git master, or wait for the 0.12 release:

IPython 0.12.dev -- An enhanced Interactive Python.
?         -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help      -> Python's own help system.
object?   -> Details about 'object', use 'object??' for extra details.

In [1]: from __future__ import  braces
SyntaxError: not a chance (, line 1)