`ParameterType`

class openff.toolkit.typing.engines.smirnoff.parameters.ParameterType(smirks, allow_cosmetic_attributes=False, **kwargs)[source]

Base class for SMIRNOFF parameter types.

This base class provides utilities to create new parameter types. See the below for examples of how to do this.

Warning

This API is experimental and subject to change.

Attributes:

smirks – The SMIRKS pattern that this parameter matches.
id – An optional identifier for the parameter.
parent_id – Optionally, the identifier of the parameter of which this parameter is a specialization.

Examples

This class allows to define new parameter types by just listing its attributes. In the example below, _ELEMENT_NAME is used to describe the SMIRNOFF parameter being defined, and is used during automatic serialization/deserialization into a dict.

>>> class MyBondParameter(ParameterType):
...     _ELEMENT_NAME = 'Bond'
...     length = ParameterAttribute(unit=unit.angstrom)
...     k = ParameterAttribute(unit=unit.kilocalorie / unit.mole / unit.angstrom**2)
...

The parameter automatically inherits the required smirks attribute from ParameterType. Associating a unit to a ParameterAttribute cause the attribute to accept only values in compatible units and to parse string expressions.

>>> my_par = MyBondParameter(
...     smirks='[*:1]-[*:2]',
...     length='1.01 * angstrom',
...     k=5 * unit.kilocalorie / unit.mole / unit.angstrom**2
... )
>>> my_par.length
<Quantity(1.01, 'angstrom')>
>>> my_par.k = 3.0 * unit.gram
Traceback (most recent call last):
...
openff.toolkit.utils.exceptions.IncompatibleUnitError:
k=3.0 gram should have units of kilocalorie / angstrom ** 2 / mole

Each attribute can be made optional by specifying a default value, and you can attach a converter function by passing a callable as an argument or through the decorator syntax.

>>> class MyParameterType(ParameterType):
...     _ELEMENT_NAME = 'Atom'
...
...     attr_optional = ParameterAttribute(default=2)
...     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 floats
...         # 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 = MyParameterType(smirks='[*:1]', attr_all_to_float='3.0', attr_int_to_float=1)
>>> my_par.attr_optional
2
>>> my_par.attr_all_to_float
3.0
>>> my_par.attr_int_to_float
1.0

The float() function can convert strings to integers, but our custom converter forbids it

>>> my_par.attr_all_to_float = '2.0'
>>> my_par.attr_int_to_float = '4.0'
Traceback (most recent call last):
...
TypeError: Cannot convert '4.0' to float

Parameter attributes that can be indexed can be handled with the IndexedParameterAttribute. These support unit validation and converters exactly as ParameterAttributes, but the validation/conversion is performed for each indexed attribute.

>>> class MyTorsionType(ParameterType):
...     _ELEMENT_NAME = 'Proper'
...     periodicity = IndexedParameterAttribute(converter=int)
...     k = IndexedParameterAttribute(unit=unit.kilocalorie / unit.mole)
...
>>> my_par = MyTorsionType(
...     smirks='[*:1]-[*:2]-[*:3]-[*:4]',
...     periodicity1=2,
...     k1=5 * unit.kilocalorie / unit.mole,
...     periodicity2='3',
...     k2=6 * unit.kilocalorie / unit.mole,
... )
>>> my_par.periodicity
[2, 3]

Indexed attributes, can be accessed both as a list or as their indexed parameter name.

>>> my_par.periodicity2 = 6
>>> my_par.periodicity[0] = 1
>>> my_par.periodicity
[1, 6]

__init__(smirks, allow_cosmetic_attributes=False, **kwargs)[source]

Create a ParameterType.

Parameters:

smirks – The SMIRKS match for the provided parameter type.
allow_cosmetic_attributes – 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__`(smirks[, allow_cosmetic_attributes])	Create a ParameterType.
`add_cosmetic_attribute`(attr_name, attr_value)	Add a cosmetic attribute to this object.
`attribute_is_cosmetic`(attr_name)	Determine whether an attribute of this object is cosmetic.
`delete_cosmetic_attribute`(attr_name)	Delete a cosmetic attribute from this object.
`to_dict`([discard_cosmetic_attributes, ...])	Convert this object to dict format.

Attributes

`id`
`parent_id`
`smirks`

add_cosmetic_attribute(attr_name, attr_value)

Add a cosmetic attribute to this object.

This attribute will not have a functional effect on the object in the OpenFF 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 – Name of the attribute to define for this object.
attr_value – The value of the attribute to define for this object.

attribute_is_cosmetic(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 – The attribute name to check
Returns:: is_cosmetic – Returns True if the attribute is defined and is cosmetic. Returns False otherwise.

delete_cosmetic_attribute(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 – Name of the cosmetic attribute to delete.

to_dict(discard_cosmetic_attributes: bool = False, duplicate_attributes: list[str] | None = None) → dict

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 – Whether to discard non-spec attributes of this object
duplicate_attributes – A list of names of attributes that redundantly decsribe data and should be discarded during serializaiton

Returns:

smirnoff_dict – The SMIRNOFF-compliant dict representation of this object.