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96 lines
3.8 KiB
Python
96 lines
3.8 KiB
Python
__all__ = ['deque', 'defaultdict', 'named_tuple']
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from _collections import deque, defaultdict
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from operator import itemgetter as _itemgetter
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import sys as _sys
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def named_tuple(typename, field_names, verbose=False):
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"""Returns a new subclass of tuple with named fields.
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>>> Point = named_tuple('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] # works just like the tuple (11, 22)
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33
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>>> x, y = p # unpacks just like a 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 a named field
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Point(x=100, y=22)
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"""
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# Parse and validate the field names
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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(field_names)
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if not ''.join((typename,) + field_names).replace('_', '').isalnum():
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raise ValueError('Type names and field names can only contain alphanumeric characters and underscores')
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if any(name.startswith('__') and name.endswith('__') for name in field_names):
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raise ValueError('Field names cannot start and end with double underscores')
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if any(name[:1].isdigit() for name in field_names):
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raise ValueError('Field names cannot start with a number')
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if len(field_names) != len(set(field_names)):
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raise ValueError('Encountered duplicate field name')
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# Create and fill-in the class template
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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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template = '''class %(typename)s(tuple):
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'%(typename)s(%(argtxt)s)'
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__slots__ = ()
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__fields__ = %(field_names)r
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def __new__(cls, %(argtxt)s):
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return tuple.__new__(cls, (%(argtxt)s))
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def __repr__(self):
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return '%(typename)s(%(reprtxt)s)' %% self
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def __asdict__(self, dict=dict, zip=zip):
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'Return a new dict mapping field names to their values'
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return dict(zip(%(field_names)r, self))
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def __replace__(self, field, value, dict=dict, zip=zip):
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'Return a new %(typename)s object replacing one field with a new value'
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return %(typename)s(**dict(zip(%(field_names)r, self) + [(field, value)])) \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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if verbose:
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print template
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# Execute the template string in a temporary namespace
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namespace = dict(itemgetter=_itemgetter)
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try:
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exec template in namespace
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except SyntaxError, e:
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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['__name__']
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return result
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if __name__ == '__main__':
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# verify that instances can be pickled
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from cPickle import loads, dumps
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Point = named_tuple('Point', 'x, y', True)
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p = Point(x=10, y=20)
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assert p == loads(dumps(p))
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import doctest
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TestResults = named_tuple('TestResults', 'failed attempted')
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print TestResults(*doctest.testmod())
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