I’m working in Django. In Django, when you’re rendering a template you send it a context dictionary to get replaced. Because I’m lazy/DRY, i often use locals() as a shortcut instead of sending a dictionary that looks like {‘my_var’: my_var, ‘var2’: var2}.
This usually works beautifully, and saves a lot of mind-numbing repetition.
I’m using django-notifications to send emails when certain events happen – say you receive a private message. Django-notifications comes with a built-in queuing feature that I am integrating now.
However, the problem is that django-notifications pickles the context dictionary at queue time. This is where the locals() trick fails — the dictionary from locals has a LOT of crap in it beyond the local variables (e.g. it has import and int()). The dictionary created by locals doesn’t pickle.
I see three options: 1) rewrite the queueing method of django-notifications to render the template before it is stored (straightforward but a bit tedious and breaks upgradability) 2) stop using the locals trick and start repeating myself 3) Try to find a lighter-weight version of locals (or a way to pickle locals).
I’m here hoping someone has leads in the direction of #3.
In case it might be relevant, here is the error I get when I try to pickle using the locals() shortcut:
TypeError: can't pickle ellipsis objects
Further, the dictionary output of locals():
{
'__builtins__':
{
'bytearray': <type 'bytearray'>,
'IndexError': <type 'exceptions.IndexError'>,
'all': <built-in function all>,
'help': Type help() for interactive help,
or help(object) for help about object.,
'vars': <built-in function vars>,
'SyntaxError': <type 'exceptions.SyntaxError'>,
'unicode': <type 'unicode'>,
'UnicodeDecodeError': <type 'exceptions.UnicodeDecodeError'>,
'isinstance': <built-in function isinstance>,
'copyright': Copyright (c) 2001-2010 Python Software Foundation.
All Rights Reserved.
Copyright (c) 2000 BeOpen.com.
All Rights Reserved.
Copyright (c) 1995-2001 Corporation for National Research Initiatives.
All Rights Reserved.
Copyright (c) 1991-1995 Stichting Mathematisch Centrum,
Amsterdam.
All Rights Reserved.,
'NameError': <type 'exceptions.NameError'>,
'BytesWarning': <type 'exceptions.BytesWarning'>,
'dict': <type 'dict'>,
'input': <built-in function input>,
'oct': <built-in function oct>,
'bin': <built-in function bin>,
'SystemExit': <type 'exceptions.SystemExit'>,
'StandardError': <type 'exceptions.StandardError'>,
'format': <built-in function format>,
'repr': <built-in function repr>,
'sorted': <built-in function sorted>,
'False': False,
'RuntimeWarning': <type 'exceptions.RuntimeWarning'>,
'list': <type 'list'>,
'iter': <built-in function iter>,
'reload': <built-in function reload>,
'Warning': <type 'exceptions.Warning'>,
'__package__': None,
'round': <built-in function round>,
'dir': <built-in function dir>,
'cmp': <built-in function cmp>,
'set': <type 'set'>,
'bytes': <type 'str'>,
'reduce': <built-in function reduce>,
'intern': <built-in function intern>,
'issubclass': <built-in function issubclass>,
'Ellipsis': Ellipsis,
'EOFError': <type 'exceptions.EOFError'>,
'locals': <built-in function locals>,
'BufferError': <type 'exceptions.BufferError'>,
'slice': <type 'slice'>,
'FloatingPointError': <type 'exceptions.FloatingPointError'>,
'sum': <built-in function sum>,
'getattr': <built-in function getattr>,
'abs': <built-in function abs>,
'exit': Use exit() or Ctrl-D (i.e. EOF) to exit,
'print': <built-in function print>,
'True': True,
'FutureWarning': <type 'exceptions.FutureWarning'>,
'ImportWarning': <type 'exceptions.ImportWarning'>,
'None': None,
'hash': <built-in function hash>,
'ReferenceError': <type 'exceptions.ReferenceError'>,
'len': <built-in function len>,
'credits': Thanks to CWI,
CNRI,
BeOpen.com,
Zope Corporation and a cast of thousands
for supporting Python development. See www.python.org for more information.,
'frozenset': <type 'frozenset'>,
'__name__': '__builtin__',
'ord': <built-in function ord>,
'super': <type 'super'>,
'_': None,
'TypeError': <type 'exceptions.TypeError'>,
'license': Type license() to see the full license text,
'KeyboardInterrupt': <type 'exceptions.KeyboardInterrupt'>,
'UserWarning': <type 'exceptions.UserWarning'>,
'filter': <built-in function filter>,
'range': <built-in function range>,
'staticmethod': <type 'staticmethod'>,
'SystemError': <type 'exceptions.SystemError'>,
'BaseException': <type 'exceptions.BaseException'>,
'pow': <built-in function pow>,
'RuntimeError': <type 'exceptions.RuntimeError'>,
'float': <type 'float'>,
'MemoryError': <type 'exceptions.MemoryError'>,
'StopIteration': <type 'exceptions.StopIteration'>,
'globals': <built-in function globals>,
'divmod': <built-in function divmod>,
'enumerate': <type 'enumerate'>,
'apply': <built-in function apply>,
'LookupError': <type 'exceptions.LookupError'>,
'open': <built-in function open>,
'quit': Use quit() or Ctrl-D (i.e. EOF) to exit,
'basestring': <type 'basestring'>,
'UnicodeError': <type 'exceptions.UnicodeError'>,
'zip': <built-in function zip>,
'hex': <built-in function hex>,
'long': <type 'long'>,
'next': <built-in function next>,
'ImportError': <type 'exceptions.ImportError'>,
'chr': <built-in function chr>,
'xrange': <type 'xrange'>,
'type': <type 'type'>,
'__doc__': "Built-in functions,
exceptions,
and other objects.\n\nNoteworthy: None is the `nil' object; Ellipsis represents `...' in slices.",
'Exception': <type 'exceptions.Exception'>,
'tuple': <type 'tuple'>,
'UnicodeTranslateError': <type 'exceptions.UnicodeTranslateError'>,
'reversed': <type 'reversed'>,
'UnicodeEncodeError': <type 'exceptions.UnicodeEncodeError'>,
'IOError': <type 'exceptions.IOError'>,
'hasattr': <built-in function hasattr>,
'delattr': <built-in function delattr>,
'setattr': <built-in function setattr>,
'raw_input': <built-in function raw_input>,
'SyntaxWarning': <type 'exceptions.SyntaxWarning'>,
'compile': <built-in function compile>,
'ArithmeticError': <type 'exceptions.ArithmeticError'>,
'str': <type 'str'>,
'property': <type 'property'>,
'GeneratorExit': <type 'exceptions.GeneratorExit'>,
'int': <type 'int'>,
'__import__': <built-in function __import__>,
'KeyError': <type 'exceptions.KeyError'>,
'coerce': <built-in function coerce>,
'PendingDeprecationWarning': <type 'exceptions.PendingDeprecationWarning'>,
'file': <type 'file'>,
'EnvironmentError': <type 'exceptions.EnvironmentError'>,
'unichr': <built-in function unichr>,
'id': <built-in function id>,
'OSError': <type 'exceptions.OSError'>,
'DeprecationWarning': <type 'exceptions.DeprecationWarning'>,
'min': <built-in function min>,
'UnicodeWarning': <type 'exceptions.UnicodeWarning'>,
'execfile': <built-in function execfile>,
'any': <built-in function any>,
'complex': <type 'complex'>,
'bool': <type 'bool'>,
'ValueError': <type 'exceptions.ValueError'>,
'NotImplemented': NotImplemented,
'map': <built-in function map>,
'buffer': <type 'buffer'>,
'max': <built-in function max>,
'object': <type 'object'>,
'TabError': <type 'exceptions.TabError'>,
'callable': <built-in function callable>,
'ZeroDivisionError': <type 'exceptions.ZeroDivisionError'>,
'eval': <built-in function eval>,
'__debug__': True,
'IndentationError': <type 'exceptions.IndentationError'>,
'AssertionError': <type 'exceptions.AssertionError'>,
'classmethod': <type 'classmethod'>,
'UnboundLocalError': <type 'exceptions.UnboundLocalError'>,
'NotImplementedError': <type 'exceptions.NotImplementedError'>,
'AttributeError': <type 'exceptions.AttributeError'>,
'OverflowError': <type 'exceptions.OverflowError'>
},
'notification': <module 'notification.models' from '/home/b/webapps/myapp/notification/models.pyc'>,
'u': <User: abcd>,
'User': <class 'django.contrib.auth.models.User'>
}
No. Its worth repeating yourself if you are going to pickle. Lots of objects, some of them unintuitive, are unable to be pickled (i.e. form input).
The locals() shortcut should only be used when you are certain that the template will be rendered immediately.