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Sync-up named tuples with the latest version of the ASPN recipe.

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Allows optional commas in the field-name spec (help when named tuples are used in conjuction with sql queries).
Adds the __fields__ attribute for introspection and to support conversion to dictionary form.
Adds a  __replace__() method similar to str.replace() but using a named field as a target.
Clean-up spelling and presentation in doc-strings.
This commit is contained in:
Raymond Hettinger 2007-09-17 00:55:00 +00:00
parent bf10c47389
commit d36a60e1e3
3 changed files with 61 additions and 13 deletions
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29
Lib/collections.py
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@ -8,33 +8,42 @@ def NamedTuple(typename, s):
"""Returns a new subclass of tuple with named fields.
>>> Point = NamedTuple('Point', 'x y')
>>> Point.__doc__ # docstring for the new class
>>> 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)
>>> 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 = p # unpacks just like a tuple
>>> x, y
(11, 22)
>>> p.x + p.y # fields also accessable by name
>>> p.x + p.y # fields also accessable by name
33
>>> p # readable __repr__ with name=value style
>>> p # readable __repr__ with name=value style
Point(x=11, y=22)
>>> p.__replace__('x', 100) # __replace__() is like str.replace() but targets a named field
Point(x=100, y=22)
>>> d = dict(zip(p.__fields__, p)) # use __fields__ to make a dictionary
>>> d['x']
11
"""
field_names = s.split()
if not ''.join([typename] + field_names).replace('_', '').isalnum():
field_names = tuple(s.replace(',', ' ').split()) # names separated by spaces and/or commas
if not ''.join((typename,) + field_names).replace('_', '').isalnum():
raise ValueError('Type names and field names can only contain alphanumeric characters and underscores')
argtxt = ', '.join(field_names)
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 __replace__(self, field, value):
'Return a new %(typename)s object replacing one field with a new value'
return %(typename)s(**dict(zip(%(field_names)r, self) + [(field, value)]))
''' % locals()
for i, name in enumerate(field_names):
template += '\n %s = property(itemgetter(%d))\n' % (name, i)
@ -51,9 +60,9 @@ def NamedTuple(typename, s):
if __name__ == '__main__':
# verify that instances are pickable
# verify that instances can be pickled
from cPickle import loads, dumps
Point = NamedTuple('Point', 'x y')
Point = NamedTuple('Point', 'x, y')
p = Point(x=10, y=20)
assert p == loads(dumps(p))