IPython/parallel/error.py

# encoding: utf-8

"""Classes and functions for kernel related errors and exceptions.

Inheritance diagram:

.. inheritance-diagram:: IPython.parallel.error
   :parts: 3

Authors:

* Brian Granger
* Min RK
"""
from __future__ import print_function

import sys
import traceback

__docformat__ = "restructuredtext en"

# Tell nose to skip this module
__test__ = {}

#-------------------------------------------------------------------------------
#  Copyright (C) 2008-2011  The IPython Development Team
#
#  Distributed under the terms of the BSD License.  The full license is in
#  the file COPYING, distributed as part of this software.
#-------------------------------------------------------------------------------

#-------------------------------------------------------------------------------
# Error classes
#-------------------------------------------------------------------------------
class IPythonError(Exception):
    """Base exception that all of our exceptions inherit from.

    This can be raised by code that doesn't have any more specific
    information."""

    pass

class KernelError(IPythonError):
    pass

class NoEnginesRegistered(KernelError):
    pass

class TaskAborted(KernelError):
    pass

class TaskTimeout(KernelError):
    pass

class TimeoutError(KernelError):
    pass

class UnmetDependency(KernelError):
    pass

class ImpossibleDependency(UnmetDependency):
    pass

class DependencyTimeout(ImpossibleDependency):
    pass

class InvalidDependency(ImpossibleDependency):
    pass

class RemoteError(KernelError):
    """Error raised elsewhere"""
    ename=None
    evalue=None
    traceback=None
    engine_info=None

    def __init__(self, ename, evalue, traceback, engine_info=None):
        self.ename=ename
        self.evalue=evalue
        self.traceback=traceback
        self.engine_info=engine_info or {}
        self.args=(ename, evalue)

    def __repr__(self):
        engineid = self.engine_info.get('engine_id', ' ')
        return "<Remote[%s]:%s(%s)>"%(engineid, self.ename, self.evalue)

    def __str__(self):
        return "%s(%s)" % (self.ename, self.evalue)
    
    def render_traceback(self):
        """render traceback to a list of lines"""
        return (self.traceback or "No traceback available").splitlines()
    
    def _render_traceback_(self):
        """Special method for custom tracebacks within IPython.
        
        This will be called by IPython instead of displaying the local traceback.
        
        It should return a traceback rendered as a list of lines.
        """
        return self.render_traceback()
    
    def print_traceback(self, excid=None):
        """print my traceback"""
        print('\n'.join(self.render_traceback()))

    


class TaskRejectError(KernelError):
    """Exception to raise when a task should be rejected by an engine.

    This exception can be used to allow a task running on an engine to test
    if the engine (or the user's namespace on the engine) has the needed
    task dependencies.  If not, the task should raise this exception.  For
    the task to be retried on another engine, the task should be created
    with the `retries` argument > 1.

    The advantage of this approach over our older properties system is that
    tasks have full access to the user's namespace on the engines and the
    properties don't have to be managed or tested by the controller.
    """


class CompositeError(RemoteError):
    """Error for representing possibly multiple errors on engines"""
    tb_limit = 4 # limit on how many tracebacks to draw
    
    def __init__(self, message, elist):
        Exception.__init__(self, *(message, elist))
        # Don't use pack_exception because it will conflict with the .message
        # attribute that is being deprecated in 2.6 and beyond.
        self.msg = message
        self.elist = elist
        self.args = [ e[0] for e in elist ]

    def _get_engine_str(self, ei):
        if not ei:
            return '[Engine Exception]'
        else:
            return '[%s:%s]: ' % (ei['engine_id'], ei['method'])

    def _get_traceback(self, ev):
        try:
            tb = ev._ipython_traceback_text
        except AttributeError:
            return 'No traceback available'
        else:
            return tb

    def __str__(self):
        s = str(self.msg)
        for en, ev, etb, ei in self.elist[:self.tb_limit]:
            engine_str = self._get_engine_str(ei)
            s = s + '\n' + engine_str + en + ': ' + str(ev)
        if len(self.elist) > self.tb_limit:
            s = s + '\n.... %i more exceptions ...' % (len(self.elist) - self.tb_limit)
        return s

    def __repr__(self):
        return "CompositeError(%i)" % len(self.elist)
    
    def render_traceback(self, excid=None):
        """render one or all of my tracebacks to a list of lines"""
        lines = []
        if excid is None:
            for (en,ev,etb,ei) in self.elist[:self.tb_limit]:
                lines.append(self._get_engine_str(ei))
                lines.extend((etb or 'No traceback available').splitlines())
                lines.append('')
            if len(self.elist) > self.tb_limit:
                lines.append(
                    '... %i more exceptions ...' % (len(self.elist) - self.tb_limit)
                )
        else:
            try:
                en,ev,etb,ei = self.elist[excid]
            except:
                raise IndexError("an exception with index %i does not exist"%excid)
            else:
                lines.append(self._get_engine_str(ei))
                lines.extend((etb or 'No traceback available').splitlines())
        
        return lines
    
    def print_traceback(self, excid=None):
        print('\n'.join(self.render_traceback(excid)))

    def raise_exception(self, excid=0):
        try:
            en,ev,etb,ei = self.elist[excid]
        except:
            raise IndexError("an exception with index %i does not exist"%excid)
        else:
            raise RemoteError(en, ev, etb, ei)


def collect_exceptions(rdict_or_list, method='unspecified'):
    """check a result dict for errors, and raise CompositeError if any exist.
    Passthrough otherwise."""
    elist = []
    if isinstance(rdict_or_list, dict):
        rlist = rdict_or_list.values()
    else:
        rlist = rdict_or_list
    for r in rlist:
        if isinstance(r, RemoteError):
            en, ev, etb, ei = r.ename, r.evalue, r.traceback, r.engine_info
            # Sometimes we could have CompositeError in our list.  Just take
            # the errors out of them and put them in our new list.  This
            # has the effect of flattening lists of CompositeErrors into one
            # CompositeError
            if en=='CompositeError':
                for e in ev.elist:
                    elist.append(e)
            else:
                elist.append((en, ev, etb, ei))
    if len(elist)==0:
        return rdict_or_list
    else:
        msg = "one or more exceptions from call to method: %s" % (method)
        # This silliness is needed so the debugger has access to the exception
        # instance (e in this case)
        try:
            raise CompositeError(msg, elist)
        except CompositeError as e:
            raise e

def wrap_exception(engine_info={}):
    etype, evalue, tb = sys.exc_info()
    stb = traceback.format_exception(etype, evalue, tb)
    exc_content = {
        'status' : 'error',
        'traceback' : stb,
        'ename' : unicode(etype.__name__),
        'evalue' : unicode(evalue),
        'engine_info' : engine_info
    }
    return exc_content

def unwrap_exception(content):
    err = RemoteError(content['ename'], content['evalue'],
                ''.join(content['traceback']),
                content.get('engine_info', {}))
    return err