"""
This module contains a backport for collections.namedtuple obtained from
http://code.activestate.com/recipes/500261-named-tuples/
"""
import sys as _sys
from keyword import iskeyword as _iskeyword
from operator import itemgetter as _itemgetter
# pylint: disable=I0011,R0914,W0122,W0612,C0103,W0212,R0912
[docs]def namedtuple(typename, field_names, verbose=False, rename=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] # indexable like a plain tuple
33
>>> x, y = p # unpack like a regular tuple
>>> x, y
(11, 22)
>>> p.x + p.y # fields also accessible 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 named fields
Point(x=100, y=22)
http://code.activestate.com/recipes/500261-named-tuples/
:codeauthor: Raymond Hettinger
:license: PSF
Changes:
* autopep8 reformatting
"""
# Parse and validate the field names. Validation serves two purposes,
# generating informative error messages and preventing template injection
# attacks.
if isinstance(field_names, basestring):
field_names = field_names.replace(
',', ' ').split() # names separated by whitespace and/or commas
field_names = tuple(map(str, field_names))
if rename:
names = list(field_names)
seen = set()
for i, name in enumerate(names):
if (not min(c.isalnum() or c == '_' for c in name) or
_iskeyword(name) or
not name or
name[0].isdigit() or
name.startswith('_') or
name in seen):
names[i] = '_%d' % i
seen.add(name)
field_names = tuple(names)
for name in (typename,) + field_names:
if not min(c.isalnum() or c == '_' for c in name):
raise ValueError(
'Type names and field names can only contain alphanumeric '
'characters and underscores: %r' % name)
if _iskeyword(name):
raise ValueError(
'Type names and field names cannot be a keyword: %r' % name)
if name[0].isdigit():
raise ValueError(
'Type names and field names cannot start with a '
'number: %r' % name)
seen_names = set()
for name in field_names:
if name.startswith('_') and not rename:
raise ValueError(
'Field names cannot start with an underscore: %r' % name)
if name in seen_names:
raise ValueError('Encountered duplicate field name: %r' % name)
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)
template = '''class %(typename)s(tuple):
'%(typename)s(%(argtxt)s)' \n
__slots__ = () \n
_fields = %(field_names)r \n
def __new__(_cls, %(argtxt)s):
return _tuple.__new__(_cls, (%(argtxt)s)) \n
@classmethod
def _make(cls, iterable, new=tuple.__new__, len=len):
'Make a new %(typename)s object from a sequence or iterable'
result = 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(self):
'Return a new dict which maps field names to their values'
return dict(zip(self._fields, self)) \n
def _replace(_self, **kwds):
'Return a new %(typename)s object replacing specified fields with new values'
result = _self._make(map(kwds.pop, %(field_names)r, _self))
if kwds:
raise ValueError('Got unexpected field names: %%r' %% kwds.keys())
return result \n
def __getnewargs__(self):
return tuple(self) \n\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, __name__='namedtuple_%s' % typename,
_property=property, _tuple=tuple)
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 environments where
# sys._getframe is not defined (Jython for example) or sys._getframe is not
# defined for arguments greater than 0 (IronPython).
try:
result.__module__ = _sys._getframe(
1).f_globals.get('__name__', '__main__')
except (AttributeError, ValueError):
pass
return result