# openforcefield.typing.engines.smirnoff.parameters.BondHandler.BondType

class `openforcefield.typing.engines.smirnoff.parameters.BondHandler.``BondType`(smirks, allow_cosmetic_attributes=False, **kwargs)

  A SMIRNOFF bond type

  Warning

  This API is experimental and subject to change.

  Attributes
    id

      A descriptor for `ParameterType` attributes.

      The descriptors allows associating to the parameter a default value, which makes the attribute optional, a unit, and a custom converter.

      Because we may want to have `None` as a default value, required attributes have the `default` set to the special type `UNDEFINED`.

      Converters can be both static or instance functions/methods with respective signatures

      converter(value): -> converted_value converter(instance, parameter_attribute, value): -> converted_value

      A decorator syntax is available (see example below).

      defaultobject, optional

        When specified, the descriptor makes this attribute optional by attaching a default value to it.

      unitsimtk.unit.Quantity, optional

        When specified, only quantities with compatible units are allowed to be set, and string expressions are automatically parsed into a `Quantity`.

      convertercallable, optional

        An optional function that can be used to convert values before setting the attribute.

      IndexedParameterAttribute

        A parameter attribute with multiple terms.

      Create a parameter type with an optional and a required attribute.

          >>> class MyParameter:
          ...     attr_required = ParameterAttribute()
          ...     attr_optional = ParameterAttribute(default=2)
          ...
          >>> my_par = MyParameter()

      Even without explicit assignment, the default value is returned.

          >>> my_par.attr_optional
          2

      If you try to access an attribute without setting it first, an exception is raised.

          >>> my_par.attr_required
          Traceback (most recent call last):
          ...
          AttributeError: 'MyParameter' object has no attribute '_attr_required'

      The attribute allow automatic conversion and validation of units.

          >>> from simtk import unit
          >>> class MyParameter:
          ...     attr_quantity = ParameterAttribute(unit=unit.angstrom)
          ...
          >>> my_par = MyParameter()
          >>> my_par.attr_quantity = '1.0 * nanometer'
          >>> my_par.attr_quantity
          Quantity(value=1.0, unit=nanometer)
          >>> my_par.attr_quantity = 3.0
          Traceback (most recent call last):
          ...
          openforcefield.utils.utils.IncompatibleUnitError: attr_quantity=3.0 dimensionless should have units of angstrom

      You can attach a custom converter to an attribute.

          >>> class MyParameter:
          ...     # Both strings and integers convert nicely to floats with float().
          ...     attr_all_to_float = ParameterAttribute(converter=float)
          ...     attr_int_to_float = ParameterAttribute()
          ...     @attr_int_to_float.converter
          ...     def attr_int_to_float(self, attr, value):
          ...         # This converter converts only integers to float
          ...         # and raise an exception for the other types.
          ...         if isinstance(value, int):
          ...             return float(value)
          ...         elif not isinstance(value, float):
          ...             raise TypeError(f"Cannot convert '{value}' to float")
          ...         return value
          ...
          >>> my_par = MyParameter()

      attr_all_to_float accepts and convert to float both strings and integers

          >>> my_par.attr_all_to_float = 1
          >>> my_par.attr_all_to_float
          1.0
          >>> my_par.attr_all_to_float = '2.0'
          >>> my_par.attr_all_to_float
          2.0

      The custom converter associated to attr_int_to_float converts only integers instead. >>> my_par.attr_int_to_float = 3 >>> my_par.attr_int_to_float 3.0 >>> my_par.attr_int_to_float = ‘4.0’ Traceback (most recent call last): … TypeError: Cannot convert ‘4.0’ to float

    k

      A descriptor for `ParameterType` attributes.

      The descriptors allows associating to the parameter a default value, which makes the attribute optional, a unit, and a custom converter.

      Because we may want to have `None` as a default value, required attributes have the `default` set to the special type `UNDEFINED`.

      Converters can be both static or instance functions/methods with respective signatures

      converter(value): -> converted_value converter(instance, parameter_attribute, value): -> converted_value

      A decorator syntax is available (see example below).

      defaultobject, optional

        When specified, the descriptor makes this attribute optional by attaching a default value to it.

      unitsimtk.unit.Quantity, optional

        When specified, only quantities with compatible units are allowed to be set, and string expressions are automatically parsed into a `Quantity`.

      convertercallable, optional

        An optional function that can be used to convert values before setting the attribute.

      IndexedParameterAttribute

        A parameter attribute with multiple terms.

      Create a parameter type with an optional and a required attribute.

          >>> class MyParameter:
          ...     attr_required = ParameterAttribute()
          ...     attr_optional = ParameterAttribute(default=2)
          ...
          >>> my_par = MyParameter()

      Even without explicit assignment, the default value is returned.

          >>> my_par.attr_optional
          2

      If you try to access an attribute without setting it first, an exception is raised.

          >>> my_par.attr_required
          Traceback (most recent call last):
          ...
          AttributeError: 'MyParameter' object has no attribute '_attr_required'

      The attribute allow automatic conversion and validation of units.

          >>> from simtk import unit
          >>> class MyParameter:
          ...     attr_quantity = ParameterAttribute(unit=unit.angstrom)
          ...
          >>> my_par = MyParameter()
          >>> my_par.attr_quantity = '1.0 * nanometer'
          >>> my_par.attr_quantity
          Quantity(value=1.0, unit=nanometer)
          >>> my_par.attr_quantity = 3.0
          Traceback (most recent call last):
          ...
          openforcefield.utils.utils.IncompatibleUnitError: attr_quantity=3.0 dimensionless should have units of angstrom

      You can attach a custom converter to an attribute.

          >>> class MyParameter:
          ...     # Both strings and integers convert nicely to floats with float().
          ...     attr_all_to_float = ParameterAttribute(converter=float)
          ...     attr_int_to_float = ParameterAttribute()
          ...     @attr_int_to_float.converter
          ...     def attr_int_to_float(self, attr, value):
          ...         # This converter converts only integers to float
          ...         # and raise an exception for the other types.
          ...         if isinstance(value, int):
          ...             return float(value)
          ...         elif not isinstance(value, float):
          ...             raise TypeError(f"Cannot convert '{value}' to float")
          ...         return value
          ...
          >>> my_par = MyParameter()

      attr_all_to_float accepts and convert to float both strings and integers

          >>> my_par.attr_all_to_float = 1
          >>> my_par.attr_all_to_float
          1.0
          >>> my_par.attr_all_to_float = '2.0'
          >>> my_par.attr_all_to_float
          2.0

      The custom converter associated to attr_int_to_float converts only integers instead. >>> my_par.attr_int_to_float = 3 >>> my_par.attr_int_to_float 3.0 >>> my_par.attr_int_to_float = ‘4.0’ Traceback (most recent call last): … TypeError: Cannot convert ‘4.0’ to float

    length

      A descriptor for `ParameterType` attributes.

      The descriptors allows associating to the parameter a default value, which makes the attribute optional, a unit, and a custom converter.

      Because we may want to have `None` as a default value, required attributes have the `default` set to the special type `UNDEFINED`.

      Converters can be both static or instance functions/methods with respective signatures

      converter(value): -> converted_value converter(instance, parameter_attribute, value): -> converted_value

      A decorator syntax is available (see example below).

      defaultobject, optional

        When specified, the descriptor makes this attribute optional by attaching a default value to it.

      unitsimtk.unit.Quantity, optional

        When specified, only quantities with compatible units are allowed to be set, and string expressions are automatically parsed into a `Quantity`.

      convertercallable, optional

        An optional function that can be used to convert values before setting the attribute.

      IndexedParameterAttribute

        A parameter attribute with multiple terms.

      Create a parameter type with an optional and a required attribute.

          >>> class MyParameter:
          ...     attr_required = ParameterAttribute()
          ...     attr_optional = ParameterAttribute(default=2)
          ...
          >>> my_par = MyParameter()

      Even without explicit assignment, the default value is returned.

          >>> my_par.attr_optional
          2

      If you try to access an attribute without setting it first, an exception is raised.

          >>> my_par.attr_required
          Traceback (most recent call last):
          ...
          AttributeError: 'MyParameter' object has no attribute '_attr_required'

      The attribute allow automatic conversion and validation of units.

          >>> from simtk import unit
          >>> class MyParameter:
          ...     attr_quantity = ParameterAttribute(unit=unit.angstrom)
          ...
          >>> my_par = MyParameter()
          >>> my_par.attr_quantity = '1.0 * nanometer'
          >>> my_par.attr_quantity
          Quantity(value=1.0, unit=nanometer)
          >>> my_par.attr_quantity = 3.0
          Traceback (most recent call last):
          ...
          openforcefield.utils.utils.IncompatibleUnitError: attr_quantity=3.0 dimensionless should have units of angstrom

      You can attach a custom converter to an attribute.

          >>> class MyParameter:
          ...     # Both strings and integers convert nicely to floats with float().
          ...     attr_all_to_float = ParameterAttribute(converter=float)
          ...     attr_int_to_float = ParameterAttribute()
          ...     @attr_int_to_float.converter
          ...     def attr_int_to_float(self, attr, value):
          ...         # This converter converts only integers to float
          ...         # and raise an exception for the other types.
          ...         if isinstance(value, int):
          ...             return float(value)
          ...         elif not isinstance(value, float):
          ...             raise TypeError(f"Cannot convert '{value}' to float")
          ...         return value
          ...
          >>> my_par = MyParameter()

      attr_all_to_float accepts and convert to float both strings and integers

          >>> my_par.attr_all_to_float = 1
          >>> my_par.attr_all_to_float
          1.0
          >>> my_par.attr_all_to_float = '2.0'
          >>> my_par.attr_all_to_float
          2.0

      The custom converter associated to attr_int_to_float converts only integers instead. >>> my_par.attr_int_to_float = 3 >>> my_par.attr_int_to_float 3.0 >>> my_par.attr_int_to_float = ‘4.0’ Traceback (most recent call last): … TypeError: Cannot convert ‘4.0’ to float

    parent_id

      A descriptor for `ParameterType` attributes.

      The descriptors allows associating to the parameter a default value, which makes the attribute optional, a unit, and a custom converter.

      Because we may want to have `None` as a default value, required attributes have the `default` set to the special type `UNDEFINED`.

      Converters can be both static or instance functions/methods with respective signatures

      converter(value): -> converted_value converter(instance, parameter_attribute, value): -> converted_value

      A decorator syntax is available (see example below).

      defaultobject, optional

        When specified, the descriptor makes this attribute optional by attaching a default value to it.

      unitsimtk.unit.Quantity, optional

        When specified, only quantities with compatible units are allowed to be set, and string expressions are automatically parsed into a `Quantity`.

      convertercallable, optional

        An optional function that can be used to convert values before setting the attribute.

      IndexedParameterAttribute

        A parameter attribute with multiple terms.

      Create a parameter type with an optional and a required attribute.

          >>> class MyParameter:
          ...     attr_required = ParameterAttribute()
          ...     attr_optional = ParameterAttribute(default=2)
          ...
          >>> my_par = MyParameter()

      Even without explicit assignment, the default value is returned.

          >>> my_par.attr_optional
          2

      If you try to access an attribute without setting it first, an exception is raised.

          >>> my_par.attr_required
          Traceback (most recent call last):
          ...
          AttributeError: 'MyParameter' object has no attribute '_attr_required'

      The attribute allow automatic conversion and validation of units.

          >>> from simtk import unit
          >>> class MyParameter:
          ...     attr_quantity = ParameterAttribute(unit=unit.angstrom)
          ...
          >>> my_par = MyParameter()
          >>> my_par.attr_quantity = '1.0 * nanometer'
          >>> my_par.attr_quantity
          Quantity(value=1.0, unit=nanometer)
          >>> my_par.attr_quantity = 3.0
          Traceback (most recent call last):
          ...
          openforcefield.utils.utils.IncompatibleUnitError: attr_quantity=3.0 dimensionless should have units of angstrom

      You can attach a custom converter to an attribute.

          >>> class MyParameter:
          ...     # Both strings and integers convert nicely to floats with float().
          ...     attr_all_to_float = ParameterAttribute(converter=float)
          ...     attr_int_to_float = ParameterAttribute()
          ...     @attr_int_to_float.converter
          ...     def attr_int_to_float(self, attr, value):
          ...         # This converter converts only integers to float
          ...         # and raise an exception for the other types.
          ...         if isinstance(value, int):
          ...             return float(value)
          ...         elif not isinstance(value, float):
          ...             raise TypeError(f"Cannot convert '{value}' to float")
          ...         return value
          ...
          >>> my_par = MyParameter()

      attr_all_to_float accepts and convert to float both strings and integers

          >>> my_par.attr_all_to_float = 1
          >>> my_par.attr_all_to_float
          1.0
          >>> my_par.attr_all_to_float = '2.0'
          >>> my_par.attr_all_to_float
          2.0

      The custom converter associated to attr_int_to_float converts only integers instead. >>> my_par.attr_int_to_float = 3 >>> my_par.attr_int_to_float 3.0 >>> my_par.attr_int_to_float = ‘4.0’ Traceback (most recent call last): … TypeError: Cannot convert ‘4.0’ to float

    smirks

      A descriptor for `ParameterType` attributes.

      The descriptors allows associating to the parameter a default value, which makes the attribute optional, a unit, and a custom converter.

      Because we may want to have `None` as a default value, required attributes have the `default` set to the special type `UNDEFINED`.

      Converters can be both static or instance functions/methods with respective signatures

      converter(value): -> converted_value converter(instance, parameter_attribute, value): -> converted_value

      A decorator syntax is available (see example below).

      defaultobject, optional

        When specified, the descriptor makes this attribute optional by attaching a default value to it.

      unitsimtk.unit.Quantity, optional

        When specified, only quantities with compatible units are allowed to be set, and string expressions are automatically parsed into a `Quantity`.

      convertercallable, optional

        An optional function that can be used to convert values before setting the attribute.

      IndexedParameterAttribute

        A parameter attribute with multiple terms.

      Create a parameter type with an optional and a required attribute.

          >>> class MyParameter:
          ...     attr_required = ParameterAttribute()
          ...     attr_optional = ParameterAttribute(default=2)
          ...
          >>> my_par = MyParameter()

      Even without explicit assignment, the default value is returned.

          >>> my_par.attr_optional
          2

      If you try to access an attribute without setting it first, an exception is raised.

          >>> my_par.attr_required
          Traceback (most recent call last):
          ...
          AttributeError: 'MyParameter' object has no attribute '_attr_required'

      The attribute allow automatic conversion and validation of units.

          >>> from simtk import unit
          >>> class MyParameter:
          ...     attr_quantity = ParameterAttribute(unit=unit.angstrom)
          ...
          >>> my_par = MyParameter()
          >>> my_par.attr_quantity = '1.0 * nanometer'
          >>> my_par.attr_quantity
          Quantity(value=1.0, unit=nanometer)
          >>> my_par.attr_quantity = 3.0
          Traceback (most recent call last):
          ...
          openforcefield.utils.utils.IncompatibleUnitError: attr_quantity=3.0 dimensionless should have units of angstrom

      You can attach a custom converter to an attribute.

          >>> class MyParameter:
          ...     # Both strings and integers convert nicely to floats with float().
          ...     attr_all_to_float = ParameterAttribute(converter=float)
          ...     attr_int_to_float = ParameterAttribute()
          ...     @attr_int_to_float.converter
          ...     def attr_int_to_float(self, attr, value):
          ...         # This converter converts only integers to float
          ...         # and raise an exception for the other types.
          ...         if isinstance(value, int):
          ...             return float(value)
          ...         elif not isinstance(value, float):
          ...             raise TypeError(f"Cannot convert '{value}' to float")
          ...         return value
          ...
          >>> my_par = MyParameter()

      attr_all_to_float accepts and convert to float both strings and integers

          >>> my_par.attr_all_to_float = 1
          >>> my_par.attr_all_to_float
          1.0
          >>> my_par.attr_all_to_float = '2.0'
          >>> my_par.attr_all_to_float
          2.0

      The custom converter associated to attr_int_to_float converts only integers instead. >>> my_par.attr_int_to_float = 3 >>> my_par.attr_int_to_float 3.0 >>> my_par.attr_int_to_float = ‘4.0’ Traceback (most recent call last): … TypeError: Cannot convert ‘4.0’ to float

  Methods

  `add_cosmetic_attribute`(self, attr_name, …) | Add a cosmetic attribute to this object.
  `attribute_is_cosmetic`(self, attr_name) | Determine whether an attribute of this object is cosmetic.
  `delete_cosmetic_attribute`(self, attr_name) | Delete a cosmetic attribute from this object.
  `to_dict`(self[, discard_cosmetic_attributes]) | Convert this object to dict format.

  `__init__`(self, smirks, allow_cosmetic_attributes=False, **kwargs)

    Create a ParameterType.

    Parameters
      smirks str

        The SMIRKS match for the provided parameter type.

      allow_cosmetic_attributes bool optional. Default = False

        Whether to permit non-spec kwargs (“cosmetic attributes”). If True, non-spec kwargs will be stored as an attribute of this parameter which can be accessed and written out. Otherwise an exception will be raised.

  Methods

  `__init__`(self, smirks[, …]) | Create a ParameterType.
  `add_cosmetic_attribute`(self, attr_name, …) | Add a cosmetic attribute to this object.
  `attribute_is_cosmetic`(self, attr_name) | Determine whether an attribute of this object is cosmetic.
  `delete_cosmetic_attribute`(self, attr_name) | Delete a cosmetic attribute from this object.
  `to_dict`(self[, discard_cosmetic_attributes]) | Convert this object to dict format.

  Attributes

  `id` | A descriptor for `ParameterType` attributes.
  `k` | A descriptor for `ParameterType` attributes.
  `length` | A descriptor for `ParameterType` attributes.
  `parent_id` | A descriptor for `ParameterType` attributes.
  `smirks` | A descriptor for `ParameterType` attributes.

  `add_cosmetic_attribute`(self, attr_name, attr_value)

    Add a cosmetic attribute to this object.

    This attribute will not have a functional effect on the object in the Open Force Field toolkit, but can be written out during output.

    Warning

    The API for modifying cosmetic attributes is experimental and may change in the future (see issue #338).

    Parameters
      attr_name str

        Name of the attribute to define for this object.

      attr_value str

        The value of the attribute to define for this object.

  `attribute_is_cosmetic`(self, attr_name)

    Determine whether an attribute of this object is cosmetic.

    Warning

    The API for modifying cosmetic attributes is experimental and may change in the future (see issue #338).

    Parameters
      attr_name str

        The attribute name to check

    Returns
      is_cosmetic bool

        Returns True if the attribute is defined and is cosmetic. Returns False otherwise.

  `delete_cosmetic_attribute`(self, attr_name)

    Delete a cosmetic attribute from this object.

    Warning

    The API for modifying cosmetic attributes is experimental and may change in the future (see issue #338).

    Parameters
      attr_name str

        Name of the cosmetic attribute to delete.

  `to_dict`(self, discard_cosmetic_attributes=False)

    Convert this object to dict format.

    The returning dictionary contains all the `ParameterAttribute` and `IndexedParameterAttribute` as well as cosmetic attributes if `discard_cosmetic_attributes` is `False`.

    Parameters
      discard_cosmetic_attributes bool, optional. Default = False

        Whether to discard non-spec attributes of this object

    Returns
      smirnoff_dict dict

        The SMIRNOFF-compliant dict representation of this object.