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__all__ = ['deque', 'defaultdict', 'NamedTuple']
from _collections import deque, defaultdict
from operator import itemgetter as _itemgetter
import sys as _sys
def NamedTuple(typename, field_names, verbose=False):
"""Returns a new subclass of tuple with named fields.
>>> Point = NamedTuple('Point', 'x y')
>>> Point.__doc__ # docstring for the new class
'Point(x, y)'
>>> p = Point(11, y=22) # instantiate with positional args or keywords
>>> p[0] + p[1] # works just like the tuple (11, 22)
33
>>> x, y = p # unpacks just like a tuple
>>> x, y
(11, 22)
>>> p.x + p.y # fields also accessable by name
33
>>> d = p.__asdict__() # convert to a dictionary
>>> d['x']
11
>>> Point(**d) # convert from a dictionary
Point(x=11, y=22)
>>> p.__replace__('x', 100) # __replace__() is like str.replace() but targets a named field
Point(x=100, y=22)
"""
# Parse and validate the field names
if isinstance(field_names, basestring):
field_names = field_names.replace(',', ' ').split() # names separated by whitespace and/or commas
field_names = tuple(field_names)
if not ''.join((typename,) + field_names).replace('_', '').isalnum():
raise ValueError('Type names and field names can only contain alphanumeric characters and underscores')
if any(name.startswith('__') and name.endswith('__') for name in field_names):
raise ValueError('Field names cannot start and end with double underscores')
# Create and fill-in the class template
argtxt = repr(field_names).replace("'", "")[1:-1] # tuple repr without parens or quotes
reprtxt = ', '.join('%s=%%r' % name for name in field_names)
template = '''class %(typename)s(tuple):
'%(typename)s(%(argtxt)s)'
__slots__ = ()
__fields__ = %(field_names)r
def __new__(cls, %(argtxt)s):
return tuple.__new__(cls, (%(argtxt)s))
def __repr__(self):
return '%(typename)s(%(reprtxt)s)' %% self
def __asdict__(self, dict=dict, zip=zip):
'Return a new dict mapping field names to their values'
return dict(zip(%(field_names)r, self))
def __replace__(self, field, value, dict=dict, zip=zip):
'Return a new %(typename)s object replacing one field with a new value'
return %(typename)s(**dict(zip(%(field_names)r, self) + [(field, value)])) \n''' % locals()
for i, name in enumerate(field_names):
template += ' %s = property(itemgetter(%d))\n' % (name, i)
if verbose:
print template
# Execute the template string in a temporary namespace
namespace = dict(itemgetter=_itemgetter)
try:
exec template in namespace
except SyntaxError, e:
raise SyntaxError(e.message + ':\n' + template)
result = namespace[typename]
# For pickling to work, the __module__ variable needs to be set to the frame
# where the named tuple is created. Bypass this step in enviroments where
# sys._getframe is not defined (Jython for example).
if hasattr(_sys, '_getframe'):
result.__module__ = _sys._getframe(1).f_globals['__name__']
return result
if __name__ == '__main__':
# verify that instances can be pickled
from cPickle import loads, dumps
Point = NamedTuple('Point', 'x, y', True)
p = Point(x=10, y=20)
assert p == loads(dumps(p))
import doctest
TestResults = NamedTuple('TestResults', 'failed attempted')
print TestResults(*doctest.testmod())
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