4.3. namedtupledefs.__init__

4.3.1. Module

The package ‘namedtupledefs’ provides a patched version of collections.namedtuple with field defaults for namedtuple.

This package provides the syntax release Python3.

4.3.2. Functions

4.3.2.1. namedtuple

namedtupledefs.__init__.namedtuple(typename, field_names, *, verbose=False, rename=False, module=None, **kargs)[source]

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)

Provides optional default values with similar behaviour to function parameters.

>>> Point = namedtuple('Point', ['x', 'y', 'z'], fielddefaults=(22, 33))

>>> Point.__doc__                   # docstring for the new class with defaults

‘Point(x, y, z) with optional default values fielddefaults=(22, 33)’

>>> Point(11)                       # instantiate with partial positional args or keywords
Point(x=11, y=22, z=33)
>>> Point(11, y=22)                 # instantiate with partial positional args or keywords
Point(x=11, y=22, z=33)
>>> p = Point(11, y=22)             # instantiate with positional args or keywords
>>> p[0] + p[1] + p[2]              # indexable like a plain tuple
66
>>> x, y, z = p                     # unpack like a regular tuple
>>> x, y, z
(11, 22, 33)
>>> p.x + p.y + p.z                 # fields also accessible by name
66
>>> d = p._asdict()                 # convert to a dictionary
>>> d['z']
33
>>> Point(**d)                      # convert from a dictionary
Point(x=11, y=22, z=33)
>>> p._replace(x=100)               # _replace() is like str.replace() but targets named fields
Point(x=100, y=22, z=33)
>>> p._replace(z=100)               # _replace() works for fields with default values as well
Point(x=11, y=22, z=100)

Args:

typename:

Name of returned class of type namedtuple. The actual registered top-level base class is namedtupledefsABC - underneath object of course.

See also usage of parameters, and [namedtuple].

field_names:

Symbolic names of fields with identical semantics as the standard library collections.namedtuple. When used in combination with the parameter fielddefaults the semantics changes to the behaviour of function parameters with default values, see [PYFUNC].

field_names := (
     <field-name>
   | <fieldnames>
)

fieldnames := '(' <field-name> [, <fieldnames>] ')'
field-name := <valid-character-one>[<field-name-tail>]
field-name-tail := <valid-character>[<field-name-tail>]
valid-character-one := [a-zA-Z]
valid-character := [a-zA-Z_0-9]

See also usage of parameters, and [namedtuple].

module

Sets ‘__module__’ of the created class definition. Available beginning with Python-3.6.

See also usage of parameters, and [namedtuple].

rename

If True replaces silently invalid field names by ‘_<item-index>’. Available beginning with Python-2.7, in Python3 beginning with Python-3.1 - so not in Python-3.0.

See also usage of parameters, and [namedtuple].

verbose

Prints created class definition.

See also usage of parameters, and [namedtuple].

kargs:

fielddefaults

Optional support for default values of fieldnames. A list of values. Same semantics as the function call interfaces [PYFUNC],

fielddefaults := '(' <item-default> [, <fielddefaults>] ')'
item-default := '(' <key>, <value> ')'
key := (<item-index> | <item-name>)
value := <default-value>
Returns:

A named tuple class.

Raises:

TypeError

ValueError

SyntaxError

4.3.3. Classes

Dynamic Created namedtuple

The factory function creates a dynamic class by the compilation of the following string. This is performed for each created namedtuple.

4.3.3.1. Class Template Python2

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from builtins import property as _property, tuple as _tuple
from operator import itemgetter as _itemgetter
from collections import OrderedDict

import namedtupledefs

class {typename}(tuple):
    '''{typename}({arg_list})
    with optional default values fielddefaults={field_defaults} => {typename}({new_args})'''

    __slots__ = ()

    _fields = {field_names!r}
    _fielddefaults = {field_defaults}

    def __new__(_cls, {new_args}):
        'Create new instance of {typename}({new_args})'
        return _tuple.__new__(_cls, ({arg_list}))

    @classmethod
    def _make(cls, iterable, new=tuple.__new__, len=len):
        'Make a new {typename} object from a sequence or iterable'
        result = new(cls, iterable)
        if len(result) != {num_fields:d}:
            raise TypeError('Expected {num_fields:d} arguments, got %d' % len(result))
        return result

    def _replace(_self, **kwds):
        'Return a new {typename} 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' % list(kwds))
        return result

    def __repr__(self):
        'Return a nicely formatted representation string'
        return self.__class__.__name__ + '({repr_fmt})' % self

    def _asdict(self):
        'Return a new OrderedDict which maps field names to their values.'
        return OrderedDict(zip(self._fields, self))

    def __getnewargs__(self):
        'Return self as a plain tuple.  Used by copy and pickle.'
        return tuple(self)

    __dict__ = _property(_asdict)

    def __getstate__(self):
        'Exclude the OrderedDict from pickling'
        pass

    def _merge(self, typename, *others):
        'Add multiple "namedtuple" resulting in a new "namedtuple" of class "typename".'
        _fn = copy(self._fields)
        _fd = copy(self._fielddefaults)  # spare None-check
        _t = ()
        for o in others:
            if not hasattr(o, '_fields') or not hasattr(o, '_fielddefaults'):
                raise ValueError(
                    "supports only classes from: namedtupledefs.namedtuple " + str(o))
            # check for non-scattered function style default values
            if _fd and (not o._fielddefaults or len(o._fielddefaults) != len(o._fields)):
                raise ValueError(
                    "default values are right bound and must not be scattered: %s / %s"
                    %(str(o._fields), str(o._fielddefaults))
                    )
            _fn += o._fields
            _fd += o._fielddefaults
            _t  += o  # want the tuple values without fiddling
        # resulting names have to be valid - the tuple will check finally
        tp = namedtupledefs.namedtuple(typename, _fn, fielddefaults=_fd)
        return tp(*tuple.__add__(self, _t))

{field_defs}

4.3.3.2. Class Template Python3

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from builtins import property as _property, tuple as _tuple
from operator import itemgetter as _itemgetter
from collections import OrderedDict

import namedtupledefs

class {typename}(tuple):
    '''{typename}({arg_list})
    with optional default values fielddefaults={field_defaults} => {typename}({new_args})'''

    __slots__ = ()

    _fields = {field_names!r}
    _fielddefaults = {field_defaults}

    def __new__(_cls, {new_args}):
        'Create new instance of {typename}({new_args})'
        return _tuple.__new__(_cls, ({arg_list}))

    @classmethod
    def _make(cls, iterable, new=tuple.__new__, len=len):
        'Make a new {typename} object from a sequence or iterable'
        result = new(cls, iterable)
        if len(result) != {num_fields:d}:
            raise TypeError('Expected {num_fields:d} arguments, got %d' % len(result))
        return result

    def _replace(_self, **kwds):
        'Return a new {typename} 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' % list(kwds))
        return result

    def __repr__(self):
        'Return a nicely formatted representation string'
        return self.__class__.__name__ + '({repr_fmt})' % self

    def _asdict(self):
        'Return a new OrderedDict which maps field names to their values.'
        return OrderedDict(zip(self._fields, self))

    def __getnewargs__(self):
        'Return self as a plain tuple.  Used by copy and pickle. Does not need the fielddefaults.'
        return tuple(self)

    __dict__ = _property(_asdict)

    def __getstate__(self):
        'Exclude the OrderedDict from pickling'
        pass

    def _merge(self, typename, *others):
        'Add multiple "namedtuple" resulting in a new "namedtuple" of class "typename".'
        _fn = copy(self._fields)
        _fd = copy(self._fielddefaults)  # spare None-check
        _t = ()
        for o in others:
            if not hasattr(o, '_fields') or not hasattr(o, '_fielddefaults'):
                raise ValueError(
                    "supports only classes from: namedtupledefs.namedtuple " + str(o))
            # check for non-scattered function style default values
            if _fd and (not o._fielddefaults or len(o._fielddefaults) != len(o._fields)):
                raise ValueError(
                    "default values are right bound and must not be scattered: %s / %s"
                    %(str(o._fields), str(o._fielddefaults))
                    )
            _fn += o._fields
            _fd += o._fielddefaults
            _t  += o  # want the tuple values without fiddling
        # resulting names have to be valid - the tuple will check finally
        tp = namedtupledefs.namedtuple(typename, _fn, fielddefaults=_fd)
        return tp(*tuple.__add__(self, _t))

{field_defs}

4.3.3.3. Changed Interfaces

The following interfaces were changed from the sources of collections.namedtuple.

__new__

The parameterlist is changed from {arg_list} to {new_args}, which is generated with default values.

4.3.3.4. New Interfaces

_merge

The method merge is introduced. The method provides the addition of multiple namedtuple into a new namedtuple with a provided class name. This includes the concatenation of the fieldnames as well as the appropriate handling of the fielddefaults.

Args:
typename:

The name of the merged class.

others:

The list of instances to be merged.

Returns:

A created new namedtuple object with merged data, _fields, and fielddefaults.

Raises:

ValueError

Example:

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A = namedtuple('TestClass', ('a', 'b', 'c'), fielddefaults=(22, 33))
B = namedtuple('TestClass1', ('d', ), fielddefaults=(44,))
C = namedtuple('TestClass2', ('e', 'f',), fielddefaults=(55, 66,))

t0 = A(11,)
self.assertEqual(t0, (11, 22, 33))

t1 = B()
self.assertEqual(t1, (44,))

t2 = C()
self.assertEqual(t2, (55, 66,))

tx = t0._merge('TestClassSum', t1, t2)
self.assertEqual(tx, (11, 22, 33, 44, 55, 66,))

4.3.3.5. Remarks

_make

The _make class method creates a new object from the current class. This includes the _fielddefaults. The call could be applied by using default values.

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A = namedtuple('TestClass', ('a', 'b', 'c'), fielddefaults=(333, 444,))

t = A(1,)
a = A._make(t)
print(a)

self.assertEqual(a, (1, 333, 444))

4.3.4. Exceptions

Uses standard exceptions:

  • SyntaxError

  • TypeError

  • ValueError