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Improve namedtuple's _cast() method with a docstring, new name, and error-checking.

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Raymond Hettinger 2008-01-05 01:35:43 +00:00
parent ced4eb06e4
commit 02740f73ff
3 changed files with 32 additions and 22 deletions
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11
Lib/collections.py
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@ -54,6 +54,7 @@ def namedtuple(typename, field_names, verbose=False):
seen_names.add(name)
# Create and fill-in the class template
numfields = len(field_names)
argtxt = repr(field_names).replace("'", "")[1:-1] # tuple repr without parens or quotes
reprtxt = ', '.join('%s=%%r' % name for name in field_names)
dicttxt = ', '.join('%r: t[%d]' % (name, pos) for pos, name in enumerate(field_names))
@ -63,7 +64,13 @@ def namedtuple(typename, field_names, verbose=False):
_fields = %(field_names)r \n
def __new__(cls, %(argtxt)s):
return tuple.__new__(cls, (%(argtxt)s)) \n
_cast = classmethod(tuple.__new__) \n
@classmethod
def _make(cls, iterable):
'Make a new %(typename)s object from a sequence or iterable'
result = tuple.__new__(cls, iterable)
if len(result) != %(numfields)d:
raise TypeError('Expected %(numfields)d arguments, got %%d' %% len(result))
return result \n
def __repr__(self):
return '%(typename)s(%(reprtxt)s)' %% self \n
def _asdict(t):
@ -71,7 +78,7 @@ def namedtuple(typename, field_names, verbose=False):
return {%(dicttxt)s} \n
def _replace(self, **kwds):
'Return a new %(typename)s object replacing specified fields with new values'
return self.__class__._cast(map(kwds.get, %(field_names)r, self)) \n\n''' % locals()
return self.__class__._make(map(kwds.get, %(field_names)r, self)) \n\n''' % locals()
for i, name in enumerate(field_names):
template += ' %s = property(itemgetter(%d))\n' % (name, i)
if verbose: