templater: fix string representation of wrapped None

flatten() and stringify() skip None, which means wrappedvalue(None).show()
must return '' instead of 'None'. This isn't a problem right now, but we'll
encounter it once we start using wrapped types extensively.

mercurial/templateutil.py

@@ -1,812 +1,814 b''
 # templateutil.py - utility for template evaluation
 #
 # Copyright 2005, 2006 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import abc
 import types
 
 from .i18n import _
 from . import (
     error,
     pycompat,
     util,
 )
 from .utils import (
     dateutil,
     stringutil,
 )
 
 class ResourceUnavailable(error.Abort):
     pass
 
 class TemplateNotFound(error.Abort):
     pass
 
 class wrapped(object):
     """Object requiring extra conversion prior to displaying or processing
     as value
 
     Use unwrapvalue() or unwrapastype() to obtain the inner object.
     """
 
     __metaclass__ = abc.ABCMeta
 
     @abc.abstractmethod
     def contains(self, context, mapping, item):
         """Test if the specified item is in self
 
         The item argument may be a wrapped object.
         """
 
     @abc.abstractmethod
     def getmember(self, context, mapping, key):
         """Return a member item for the specified key
 
         The key argument may be a wrapped object.
         A returned object may be either a wrapped object or a pure value
         depending on the self type.
         """
 
     @abc.abstractmethod
     def getmin(self, context, mapping):
         """Return the smallest item, which may be either a wrapped or a pure
         value depending on the self type"""
 
     @abc.abstractmethod
     def getmax(self, context, mapping):
         """Return the largest item, which may be either a wrapped or a pure
         value depending on the self type"""
 
     @abc.abstractmethod
     def itermaps(self, context):
         """Yield each template mapping"""
 
     @abc.abstractmethod
     def join(self, context, mapping, sep):
         """Join items with the separator; Returns a bytes or (possibly nested)
         generator of bytes
 
         A pre-configured template may be rendered per item if this container
         holds unprintable items.
         """
 
     @abc.abstractmethod
     def show(self, context, mapping):
         """Return a bytes or (possibly nested) generator of bytes representing
         the underlying object
 
         A pre-configured template may be rendered if the underlying object is
         not printable.
         """
 
     @abc.abstractmethod
     def tovalue(self, context, mapping):
         """Move the inner value object out or create a value representation
 
         A returned value must be serializable by templaterfilters.json().
         """
 
 class wrappedbytes(wrapped):
     """Wrapper for byte string"""
 
     def __init__(self, value):
         self._value = value
 
     def contains(self, context, mapping, item):
         item = stringify(context, mapping, item)
         return item in self._value
 
     def getmember(self, context, mapping, key):
         raise error.ParseError(_('%r is not a dictionary')
                                % pycompat.bytestr(self._value))
 
     def getmin(self, context, mapping):
         return self._getby(context, mapping, min)
 
     def getmax(self, context, mapping):
         return self._getby(context, mapping, max)
 
     def _getby(self, context, mapping, func):
         if not self._value:
             raise error.ParseError(_('empty string'))
         return func(pycompat.iterbytestr(self._value))
 
     def itermaps(self, context):
         raise error.ParseError(_('%r is not iterable of mappings')
                                % pycompat.bytestr(self._value))
 
     def join(self, context, mapping, sep):
         return joinitems(pycompat.iterbytestr(self._value), sep)
 
     def show(self, context, mapping):
         return self._value
 
     def tovalue(self, context, mapping):
         return self._value
 
 class wrappedvalue(wrapped):
     """Generic wrapper for pure non-list/dict/bytes value"""
 
     def __init__(self, value):
         self._value = value
 
     def contains(self, context, mapping, item):
         raise error.ParseError(_("%r is not iterable") % self._value)
 
     def getmember(self, context, mapping, key):
         raise error.ParseError(_('%r is not a dictionary') % self._value)
 
     def getmin(self, context, mapping):
         raise error.ParseError(_("%r is not iterable") % self._value)
 
     def getmax(self, context, mapping):
         raise error.ParseError(_("%r is not iterable") % self._value)
 
     def itermaps(self, context):
         raise error.ParseError(_('%r is not iterable of mappings')
                                % self._value)
 
     def join(self, context, mapping, sep):
         raise error.ParseError(_('%r is not iterable') % self._value)
 
     def show(self, context, mapping):
+        if self._value is None:
+            return b''
         return pycompat.bytestr(self._value)
 
     def tovalue(self, context, mapping):
         return self._value
 
 # stub for representing a date type; may be a real date type that can
 # provide a readable string value
 class date(object):
     pass
 
 class hybrid(wrapped):
     """Wrapper for list or dict to support legacy template
 
     This class allows us to handle both:
     - "{files}" (legacy command-line-specific list hack) and
     - "{files % '{file}\n'}" (hgweb-style with inlining and function support)
     and to access raw values:
     - "{ifcontains(file, files, ...)}", "{ifcontains(key, extras, ...)}"
     - "{get(extras, key)}"
     - "{files|json}"
     """
 
     def __init__(self, gen, values, makemap, joinfmt, keytype=None):
         self._gen = gen  # generator or function returning generator
         self._values = values
         self._makemap = makemap
         self._joinfmt = joinfmt
         self._keytype = keytype  # hint for 'x in y' where type(x) is unresolved
 
     def contains(self, context, mapping, item):
         item = unwrapastype(context, mapping, item, self._keytype)
         return item in self._values
 
     def getmember(self, context, mapping, key):
         # TODO: maybe split hybrid list/dict types?
         if not util.safehasattr(self._values, 'get'):
             raise error.ParseError(_('not a dictionary'))
         key = unwrapastype(context, mapping, key, self._keytype)
         return self._wrapvalue(key, self._values.get(key))
 
     def getmin(self, context, mapping):
         return self._getby(context, mapping, min)
 
     def getmax(self, context, mapping):
         return self._getby(context, mapping, max)
 
     def _getby(self, context, mapping, func):
         if not self._values:
             raise error.ParseError(_('empty sequence'))
         val = func(self._values)
         return self._wrapvalue(val, val)
 
     def _wrapvalue(self, key, val):
         if val is None:
             return
         if util.safehasattr(val, '_makemap'):
             # a nested hybrid list/dict, which has its own way of map operation
             return val
         return mappable(None, key, val, self._makemap)
 
     def itermaps(self, context):
         makemap = self._makemap
         for x in self._values:
             yield makemap(x)
 
     def join(self, context, mapping, sep):
         # TODO: switch gen to (context, mapping) API?
         return joinitems((self._joinfmt(x) for x in self._values), sep)
 
     def show(self, context, mapping):
         # TODO: switch gen to (context, mapping) API?
         gen = self._gen
         if gen is None:
             return self.join(context, mapping, ' ')
         if callable(gen):
             return gen()
         return gen
 
     def tovalue(self, context, mapping):
         # TODO: make it non-recursive for trivial lists/dicts
         xs = self._values
         if util.safehasattr(xs, 'get'):
             return {k: unwrapvalue(context, mapping, v)
                     for k, v in xs.iteritems()}
         return [unwrapvalue(context, mapping, x) for x in xs]
 
 class mappable(wrapped):
     """Wrapper for non-list/dict object to support map operation
 
     This class allows us to handle both:
     - "{manifest}"
     - "{manifest % '{rev}:{node}'}"
     - "{manifest.rev}"
     """
 
     def __init__(self, gen, key, value, makemap):
         self._gen = gen  # generator or function returning generator
         self._key = key
         self._value = value  # may be generator of strings
         self._makemap = makemap
 
     def tomap(self):
         return self._makemap(self._key)
 
     def contains(self, context, mapping, item):
         w = makewrapped(context, mapping, self._value)
         return w.contains(context, mapping, item)
 
     def getmember(self, context, mapping, key):
         w = makewrapped(context, mapping, self._value)
         return w.getmember(context, mapping, key)
 
     def getmin(self, context, mapping):
         w = makewrapped(context, mapping, self._value)
         return w.getmin(context, mapping)
 
     def getmax(self, context, mapping):
         w = makewrapped(context, mapping, self._value)
         return w.getmax(context, mapping)
 
     def itermaps(self, context):
         yield self.tomap()
 
     def join(self, context, mapping, sep):
         w = makewrapped(context, mapping, self._value)
         return w.join(context, mapping, sep)
 
     def show(self, context, mapping):
         # TODO: switch gen to (context, mapping) API?
         gen = self._gen
         if gen is None:
             return pycompat.bytestr(self._value)
         if callable(gen):
             return gen()
         return gen
 
     def tovalue(self, context, mapping):
         return _unthunk(context, mapping, self._value)
 
 class _mappingsequence(wrapped):
     """Wrapper for sequence of template mappings
 
     This represents an inner template structure (i.e. a list of dicts),
     which can also be rendered by the specified named/literal template.
 
     Template mappings may be nested.
     """
 
     def __init__(self, name=None, tmpl=None, sep=''):
         if name is not None and tmpl is not None:
             raise error.ProgrammingError('name and tmpl are mutually exclusive')
         self._name = name
         self._tmpl = tmpl
         self._defaultsep = sep
 
     def contains(self, context, mapping, item):
         raise error.ParseError(_('not comparable'))
 
     def getmember(self, context, mapping, key):
         raise error.ParseError(_('not a dictionary'))
 
     def getmin(self, context, mapping):
         raise error.ParseError(_('not comparable'))
 
     def getmax(self, context, mapping):
         raise error.ParseError(_('not comparable'))
 
     def join(self, context, mapping, sep):
         mapsiter = _iteroverlaymaps(context, mapping, self.itermaps(context))
         if self._name:
             itemiter = (context.process(self._name, m) for m in mapsiter)
         elif self._tmpl:
             itemiter = (context.expand(self._tmpl, m) for m in mapsiter)
         else:
             raise error.ParseError(_('not displayable without template'))
         return joinitems(itemiter, sep)
 
     def show(self, context, mapping):
         return self.join(context, mapping, self._defaultsep)
 
     def tovalue(self, context, mapping):
         knownres = context.knownresourcekeys()
         items = []
         for nm in self.itermaps(context):
             # drop internal resources (recursively) which shouldn't be displayed
             lm = context.overlaymap(mapping, nm)
             items.append({k: unwrapvalue(context, lm, v)
                           for k, v in nm.iteritems() if k not in knownres})
         return items
 
 class mappinggenerator(_mappingsequence):
     """Wrapper for generator of template mappings
 
     The function ``make(context, *args)`` should return a generator of
     mapping dicts.
     """
 
     def __init__(self, make, args=(), name=None, tmpl=None, sep=''):
         super(mappinggenerator, self).__init__(name, tmpl, sep)
         self._make = make
         self._args = args
 
     def itermaps(self, context):
         return self._make(context, *self._args)
 
 class mappinglist(_mappingsequence):
     """Wrapper for list of template mappings"""
 
     def __init__(self, mappings, name=None, tmpl=None, sep=''):
         super(mappinglist, self).__init__(name, tmpl, sep)
         self._mappings = mappings
 
     def itermaps(self, context):
         return iter(self._mappings)
 
 class mappedgenerator(wrapped):
     """Wrapper for generator of strings which acts as a list
 
     The function ``make(context, *args)`` should return a generator of
     byte strings, or a generator of (possibly nested) generators of byte
     strings (i.e. a generator for a list of byte strings.)
     """
 
     def __init__(self, make, args=()):
         self._make = make
         self._args = args
 
     def contains(self, context, mapping, item):
         item = stringify(context, mapping, item)
         return item in self.tovalue(context, mapping)
 
     def _gen(self, context):
         return self._make(context, *self._args)
 
     def getmember(self, context, mapping, key):
         raise error.ParseError(_('not a dictionary'))
 
     def getmin(self, context, mapping):
         return self._getby(context, mapping, min)
 
     def getmax(self, context, mapping):
         return self._getby(context, mapping, max)
 
     def _getby(self, context, mapping, func):
         xs = self.tovalue(context, mapping)
         if not xs:
             raise error.ParseError(_('empty sequence'))
         return func(xs)
 
     def itermaps(self, context):
         raise error.ParseError(_('list of strings is not mappable'))
 
     def join(self, context, mapping, sep):
         return joinitems(self._gen(context), sep)
 
     def show(self, context, mapping):
         return self.join(context, mapping, '')
 
     def tovalue(self, context, mapping):
         return [stringify(context, mapping, x) for x in self._gen(context)]
 
 def hybriddict(data, key='key', value='value', fmt=None, gen=None):
     """Wrap data to support both dict-like and string-like operations"""
     prefmt = pycompat.identity
     if fmt is None:
         fmt = '%s=%s'
         prefmt = pycompat.bytestr
     return hybrid(gen, data, lambda k: {key: k, value: data[k]},
                   lambda k: fmt % (prefmt(k), prefmt(data[k])))
 
 def hybridlist(data, name, fmt=None, gen=None):
     """Wrap data to support both list-like and string-like operations"""
     prefmt = pycompat.identity
     if fmt is None:
         fmt = '%s'
         prefmt = pycompat.bytestr
     return hybrid(gen, data, lambda x: {name: x}, lambda x: fmt % prefmt(x))
 
 def compatdict(context, mapping, name, data, key='key', value='value',
                fmt=None, plural=None, separator=' '):
     """Wrap data like hybriddict(), but also supports old-style list template
 
     This exists for backward compatibility with the old-style template. Use
     hybriddict() for new template keywords.
     """
     c = [{key: k, value: v} for k, v in data.iteritems()]
     f = _showcompatlist(context, mapping, name, c, plural, separator)
     return hybriddict(data, key=key, value=value, fmt=fmt, gen=f)
 
 def compatlist(context, mapping, name, data, element=None, fmt=None,
                plural=None, separator=' '):
     """Wrap data like hybridlist(), but also supports old-style list template
 
     This exists for backward compatibility with the old-style template. Use
     hybridlist() for new template keywords.
     """
     f = _showcompatlist(context, mapping, name, data, plural, separator)
     return hybridlist(data, name=element or name, fmt=fmt, gen=f)
 
 def _showcompatlist(context, mapping, name, values, plural=None, separator=' '):
     """Return a generator that renders old-style list template
 
     name is name of key in template map.
     values is list of strings or dicts.
     plural is plural of name, if not simply name + 's'.
     separator is used to join values as a string
 
     expansion works like this, given name 'foo'.
 
     if values is empty, expand 'no_foos'.
 
     if 'foo' not in template map, return values as a string,
     joined by 'separator'.
 
     expand 'start_foos'.
 
     for each value, expand 'foo'. if 'last_foo' in template
     map, expand it instead of 'foo' for last key.
 
     expand 'end_foos'.
     """
     if not plural:
         plural = name + 's'
     if not values:
         noname = 'no_' + plural
         if context.preload(noname):
             yield context.process(noname, mapping)
         return
     if not context.preload(name):
         if isinstance(values[0], bytes):
             yield separator.join(values)
         else:
             for v in values:
                 r = dict(v)
                 r.update(mapping)
                 yield r
         return
     startname = 'start_' + plural
     if context.preload(startname):
         yield context.process(startname, mapping)
     def one(v, tag=name):
         vmapping = {}
         try:
             vmapping.update(v)
         # Python 2 raises ValueError if the type of v is wrong. Python
         # 3 raises TypeError.
         except (AttributeError, TypeError, ValueError):
             try:
                 # Python 2 raises ValueError trying to destructure an e.g.
                 # bytes. Python 3 raises TypeError.
                 for a, b in v:
                     vmapping[a] = b
             except (TypeError, ValueError):
                 vmapping[name] = v
         vmapping = context.overlaymap(mapping, vmapping)
         return context.process(tag, vmapping)
     lastname = 'last_' + name
     if context.preload(lastname):
         last = values.pop()
     else:
         last = None
     for v in values:
         yield one(v)
     if last is not None:
         yield one(last, tag=lastname)
     endname = 'end_' + plural
     if context.preload(endname):
         yield context.process(endname, mapping)
 
 def flatten(context, mapping, thing):
     """Yield a single stream from a possibly nested set of iterators"""
     if isinstance(thing, wrapped):
         thing = thing.show(context, mapping)
     if isinstance(thing, bytes):
         yield thing
     elif isinstance(thing, str):
         # We can only hit this on Python 3, and it's here to guard
         # against infinite recursion.
         raise error.ProgrammingError('Mercurial IO including templates is done'
                                      ' with bytes, not strings, got %r' % thing)
     elif thing is None:
         pass
     elif not util.safehasattr(thing, '__iter__'):
         yield pycompat.bytestr(thing)
     else:
         for i in thing:
             if isinstance(i, wrapped):
                 i = i.show(context, mapping)
             if isinstance(i, bytes):
                 yield i
             elif i is None:
                 pass
             elif not util.safehasattr(i, '__iter__'):
                 yield pycompat.bytestr(i)
             else:
                 for j in flatten(context, mapping, i):
                     yield j
 
 def stringify(context, mapping, thing):
     """Turn values into bytes by converting into text and concatenating them"""
     if isinstance(thing, bytes):
         return thing  # retain localstr to be round-tripped
     return b''.join(flatten(context, mapping, thing))
 
 def findsymbolicname(arg):
     """Find symbolic name for the given compiled expression; returns None
     if nothing found reliably"""
     while True:
         func, data = arg
         if func is runsymbol:
             return data
         elif func is runfilter:
             arg = data[0]
         else:
             return None
 
 def _unthunk(context, mapping, thing):
     """Evaluate a lazy byte string into value"""
     if not isinstance(thing, types.GeneratorType):
         return thing
     return stringify(context, mapping, thing)
 
 def evalrawexp(context, mapping, arg):
     """Evaluate given argument as a bare template object which may require
     further processing (such as folding generator of strings)"""
     func, data = arg
     return func(context, mapping, data)
 
 def evalwrapped(context, mapping, arg):
     """Evaluate given argument to wrapped object"""
     thing = evalrawexp(context, mapping, arg)
     return makewrapped(context, mapping, thing)
 
 def makewrapped(context, mapping, thing):
     """Lift object to a wrapped type"""
     if isinstance(thing, wrapped):
         return thing
     thing = _unthunk(context, mapping, thing)
     if isinstance(thing, bytes):
         return wrappedbytes(thing)
     return wrappedvalue(thing)
 
 def evalfuncarg(context, mapping, arg):
     """Evaluate given argument as value type"""
     return unwrapvalue(context, mapping, evalrawexp(context, mapping, arg))
 
 def unwrapvalue(context, mapping, thing):
     """Move the inner value object out of the wrapper"""
     if isinstance(thing, wrapped):
         return thing.tovalue(context, mapping)
     # evalrawexp() may return string, generator of strings or arbitrary object
     # such as date tuple, but filter does not want generator.
     return _unthunk(context, mapping, thing)
 
 def evalboolean(context, mapping, arg):
     """Evaluate given argument as boolean, but also takes boolean literals"""
     func, data = arg
     if func is runsymbol:
         thing = func(context, mapping, data, default=None)
         if thing is None:
             # not a template keyword, takes as a boolean literal
             thing = stringutil.parsebool(data)
     else:
         thing = func(context, mapping, data)
     if isinstance(thing, wrapped):
         thing = thing.tovalue(context, mapping)
     if isinstance(thing, bool):
         return thing
     # other objects are evaluated as strings, which means 0 is True, but
     # empty dict/list should be False as they are expected to be ''
     return bool(stringify(context, mapping, thing))
 
 def evaldate(context, mapping, arg, err=None):
     """Evaluate given argument as a date tuple or a date string; returns
     a (unixtime, offset) tuple"""
     thing = evalrawexp(context, mapping, arg)
     return unwrapdate(context, mapping, thing, err)
 
 def unwrapdate(context, mapping, thing, err=None):
     thing = unwrapvalue(context, mapping, thing)
     try:
         return dateutil.parsedate(thing)
     except AttributeError:
         raise error.ParseError(err or _('not a date tuple nor a string'))
     except error.ParseError:
         if not err:
             raise
         raise error.ParseError(err)
 
 def evalinteger(context, mapping, arg, err=None):
     thing = evalrawexp(context, mapping, arg)
     return unwrapinteger(context, mapping, thing, err)
 
 def unwrapinteger(context, mapping, thing, err=None):
     thing = unwrapvalue(context, mapping, thing)
     try:
         return int(thing)
     except (TypeError, ValueError):
         raise error.ParseError(err or _('not an integer'))
 
 def evalstring(context, mapping, arg):
     return stringify(context, mapping, evalrawexp(context, mapping, arg))
 
 def evalstringliteral(context, mapping, arg):
     """Evaluate given argument as string template, but returns symbol name
     if it is unknown"""
     func, data = arg
     if func is runsymbol:
         thing = func(context, mapping, data, default=data)
     else:
         thing = func(context, mapping, data)
     return stringify(context, mapping, thing)
 
 _unwrapfuncbytype = {
     None: unwrapvalue,
     bytes: stringify,
     date: unwrapdate,
     int: unwrapinteger,
 }
 
 def unwrapastype(context, mapping, thing, typ):
     """Move the inner value object out of the wrapper and coerce its type"""
     try:
         f = _unwrapfuncbytype[typ]
     except KeyError:
         raise error.ProgrammingError('invalid type specified: %r' % typ)
     return f(context, mapping, thing)
 
 def runinteger(context, mapping, data):
     return int(data)
 
 def runstring(context, mapping, data):
     return data
 
 def _recursivesymbolblocker(key):
     def showrecursion(**args):
         raise error.Abort(_("recursive reference '%s' in template") % key)
     return showrecursion
 
 def runsymbol(context, mapping, key, default=''):
     v = context.symbol(mapping, key)
     if v is None:
         # put poison to cut recursion. we can't move this to parsing phase
         # because "x = {x}" is allowed if "x" is a keyword. (issue4758)
         safemapping = mapping.copy()
         safemapping[key] = _recursivesymbolblocker(key)
         try:
             v = context.process(key, safemapping)
         except TemplateNotFound:
             v = default
     if callable(v) and getattr(v, '_requires', None) is None:
         # old templatekw: expand all keywords and resources
         # (TODO: deprecate this after porting web template keywords to new API)
         props = {k: context._resources.lookup(context, mapping, k)
                  for k in context._resources.knownkeys()}
         # pass context to _showcompatlist() through templatekw._showlist()
         props['templ'] = context
         props.update(mapping)
         return v(**pycompat.strkwargs(props))
     if callable(v):
         # new templatekw
         try:
             return v(context, mapping)
         except ResourceUnavailable:
             # unsupported keyword is mapped to empty just like unknown keyword
             return None
     return v
 
 def runtemplate(context, mapping, template):
     for arg in template:
         yield evalrawexp(context, mapping, arg)
 
 def runfilter(context, mapping, data):
     arg, filt = data
     thing = evalrawexp(context, mapping, arg)
     intype = getattr(filt, '_intype', None)
     try:
         thing = unwrapastype(context, mapping, thing, intype)
         return filt(thing)
     except error.ParseError as e:
         raise error.ParseError(bytes(e), hint=_formatfiltererror(arg, filt))
 
 def _formatfiltererror(arg, filt):
     fn = pycompat.sysbytes(filt.__name__)
     sym = findsymbolicname(arg)
     if not sym:
         return _("incompatible use of template filter '%s'") % fn
     return (_("template filter '%s' is not compatible with keyword '%s'")
             % (fn, sym))
 
 def _iteroverlaymaps(context, origmapping, newmappings):
     """Generate combined mappings from the original mapping and an iterable
     of partial mappings to override the original"""
     for i, nm in enumerate(newmappings):
         lm = context.overlaymap(origmapping, nm)
         lm['index'] = i
         yield lm
 
 def _applymap(context, mapping, d, darg, targ):
     try:
         diter = d.itermaps(context)
     except error.ParseError as err:
         sym = findsymbolicname(darg)
         if not sym:
             raise
         hint = _("keyword '%s' does not support map operation") % sym
         raise error.ParseError(bytes(err), hint=hint)
     for lm in _iteroverlaymaps(context, mapping, diter):
         yield evalrawexp(context, lm, targ)
 
 def runmap(context, mapping, data):
     darg, targ = data
     d = evalwrapped(context, mapping, darg)
     return mappedgenerator(_applymap, args=(mapping, d, darg, targ))
 
 def runmember(context, mapping, data):
     darg, memb = data
     d = evalwrapped(context, mapping, darg)
     if util.safehasattr(d, 'tomap'):
         lm = context.overlaymap(mapping, d.tomap())
         return runsymbol(context, lm, memb)
     try:
         return d.getmember(context, mapping, memb)
     except error.ParseError as err:
         sym = findsymbolicname(darg)
         if not sym:
             raise
         hint = _("keyword '%s' does not support member operation") % sym
         raise error.ParseError(bytes(err), hint=hint)
 
 def runnegate(context, mapping, data):
     data = evalinteger(context, mapping, data,
                        _('negation needs an integer argument'))
     return -data
 
 def runarithmetic(context, mapping, data):
     func, left, right = data
     left = evalinteger(context, mapping, left,
                        _('arithmetic only defined on integers'))
     right = evalinteger(context, mapping, right,
                         _('arithmetic only defined on integers'))
     try:
         return func(left, right)
     except ZeroDivisionError:
         raise error.Abort(_('division by zero is not defined'))
 
 def joinitems(itemiter, sep):
     """Join items with the separator; Returns generator of bytes"""
     first = True
     for x in itemiter:
         if first:
             first = False
         elif sep:
             yield sep
         yield x