102 lines
4.5 KiB
Python
102 lines
4.5 KiB
Python
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from keyword import iskeyword as _iskeyword
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from operator import itemgetter as _itemgetter
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import sys as _sys
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def namedtuple(typename, field_names):
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"""Returns a new subclass of tuple with named fields.
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>>> Point = namedtuple('Point', 'x y')
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>>> Point.__doc__ # docstring for the new class
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'Point(x, y)'
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>>> p = Point(11, y=22) # instantiate with positional args or keywords
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>>> p[0] + p[1] # indexable like a plain tuple
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33
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>>> x, y = p # unpack like a regular tuple
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>>> x, y
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(11, 22)
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>>> p.x + p.y # fields also accessable by name
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33
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>>> d = p._asdict() # convert to a dictionary
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>>> d['x']
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11
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>>> Point(**d) # convert from a dictionary
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Point(x=11, y=22)
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>>> p._replace(x=100) # _replace() is like str.replace() but targets named fields
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Point(x=100, y=22)
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"""
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# Parse and validate the field names. Validation serves two purposes,
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# generating informative error messages and preventing template injection attacks.
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if isinstance(field_names, basestring):
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field_names = field_names.replace(',', ' ').split() # names separated by whitespace and/or commas
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field_names = tuple(map(str, field_names))
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for name in (typename,) + field_names:
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if not all(c.isalnum() or c=='_' for c in name):
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raise ValueError('Type names and field names can only contain alphanumeric characters and underscores: %r' % name)
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if _iskeyword(name):
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raise ValueError('Type names and field names cannot be a keyword: %r' % name)
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if name[0].isdigit():
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raise ValueError('Type names and field names cannot start with a number: %r' % name)
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seen_names = set()
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for name in field_names:
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if name.startswith('_'):
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raise ValueError('Field names cannot start with an underscore: %r' % name)
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if name in seen_names:
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raise ValueError('Encountered duplicate field name: %r' % name)
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seen_names.add(name)
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# Create and fill-in the class template
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numfields = len(field_names)
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argtxt = repr(field_names).replace("'", "")[1:-1] # tuple repr without parens or quotes
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reprtxt = ', '.join('%s=%%r' % name for name in field_names)
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dicttxt = ', '.join('%r: t[%d]' % (name, pos) for pos, name in enumerate(field_names))
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template = '''class %(typename)s(tuple):
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'%(typename)s(%(argtxt)s)' \n
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__slots__ = () \n
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_fields = %(field_names)r \n
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def __new__(_cls, %(argtxt)s):
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return _tuple.__new__(_cls, (%(argtxt)s)) \n
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@classmethod
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def _make(cls, iterable, new=tuple.__new__, len=len):
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'Make a new %(typename)s object from a sequence or iterable'
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result = new(cls, iterable)
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if len(result) != %(numfields)d:
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raise TypeError('Expected %(numfields)d arguments, got %%d' %% len(result))
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return result \n
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def __repr__(self):
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return '%(typename)s(%(reprtxt)s)' %% self \n
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def _asdict(t):
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'Return a new dict which maps field names to their values'
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return {%(dicttxt)s} \n
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def _replace(_self, **kwds):
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'Return a new %(typename)s object replacing specified fields with new values'
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result = _self._make(map(kwds.pop, %(field_names)r, _self))
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if kwds:
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raise ValueError('Got unexpected field names: %%r' %% kwds.keys())
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return result \n
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def __getnewargs__(self):
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return tuple(self) \n\n''' % locals()
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for i, name in enumerate(field_names):
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template += ' %s = _property(_itemgetter(%d))\n' % (name, i)
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# Execute the template string in a temporary namespace and
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# support tracing utilities by setting a value for frame.f_globals['__name__']
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namespace = dict(_itemgetter=_itemgetter, __name__='namedtuple_%s' % typename,
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_property=property, _tuple=tuple)
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try:
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exec(template, namespace)
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except SyntaxError:
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e = _sys.exc_info()[1]
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raise SyntaxError(e.message + ':\n' + template)
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result = namespace[typename]
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# For pickling to work, the __module__ variable needs to be set to the frame
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# where the named tuple is created. Bypass this step in enviroments where
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# sys._getframe is not defined (Jython for example).
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if hasattr(_sys, '_getframe'):
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result.__module__ = _sys._getframe(1).f_globals.get('__name__', '__main__')
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return result
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