`Topology`

class openff.toolkit.topology.Topology(other=None)[source]

A Topology is a chemical representation of a system containing one or more molecules appearing in a specified order.

Warning

This API is experimental and subject to change.

Examples

Import some utilities

>>> from openmm import app
>>> from openff.toolkit.tests.utils import get_data_file_path, get_packmol_pdb_file_path
>>> pdb_filepath = get_packmol_pdb_file_path('cyclohexane_ethanol_0.4_0.6')
>>> monomer_names = ('cyclohexane', 'ethanol')

Create a Topology object from a PDB file and sdf files defining the molecular contents

>>> from openff.toolkit import Molecule, Topology
>>> pdbfile = app.PDBFile(pdb_filepath)
>>> sdf_filepaths = [get_data_file_path(f'systems/monomers/{name}.sdf') for name in monomer_names]
>>> unique_molecules = [Molecule.from_file(sdf_filepath) for sdf_filepath in sdf_filepaths]
>>> topology = Topology.from_openmm(pdbfile.topology, unique_molecules=unique_molecules)

Create a Topology object from a PDB file and IUPAC names of the molecular contents

>>> pdbfile = app.PDBFile(pdb_filepath)
>>> unique_molecules = [Molecule.from_iupac(name) for name in monomer_names]
>>> topology = Topology.from_openmm(pdbfile.topology, unique_molecules=unique_molecules)

Create an empty Topology object and add a few copies of a single benzene molecule

>>> topology = Topology()
>>> molecule = Molecule.from_iupac('benzene')
>>> molecule_topology_indices = [topology.add_molecule(molecule) for index in range(10)]

__init__(other=None)[source]

Create a new Topology.

Parameters: other (optional, default=None) – If specified, attempt to construct a copy of the Topology from the specified object. This might be a Topology object, or a file that can be used to construct a Topology object or serialized Topology object.

Methods

`__init__`([other])	Create a new Topology.
`add_constraint`(iatom, jatom[, distance])	Mark a pair of atoms as constrained.
`add_molecule`(molecule)	Add a copy of the molecule to the topology
`assert_bonded`(atom1, atom2)	Raise an exception if the specified atoms are not bonded in the topology.
`atom`(atom_topology_index)	Get the TopologyAtom at a given Topology atom index.
`atom_index`(atom)	Returns the index of a given atom in this topology
`bond`(bond_topology_index)	Get the TopologyBond at a given Topology bond index.
`chemical_environment_matches`(query[, ...])	Retrieve all matches for a given chemical environment query.
`copy_initializer`(other)
`from_bson`(serialized)	Instantiate an object from a BSON serialized representation.
`from_dict`(topology_dict)	Create a new Topology from a dictionary representation
`from_json`(serialized)	Instantiate an object from a JSON serialized representation.
`from_mdtraj`(mdtraj_topology[, unique_molecules])	Construct an OpenFF Topology object from an MDTraj Topology object.
`from_messagepack`(serialized)	Instantiate an object from a MessagePack serialized representation.
`from_molecules`(molecules)	Create a new Topology object containing one copy of each of the specified molecule(s).
`from_openmm`(openmm_topology[, unique_molecules])	Construct an OpenFF Topology object from an OpenMM Topology object.
`from_pickle`(serialized)	Instantiate an object from a pickle serialized representation.
`from_toml`(serialized)	Instantiate an object from a TOML serialized representation.
`from_xml`(serialized)	Instantiate an object from an XML serialized representation.
`from_yaml`(serialized)	Instantiate from a YAML serialized representation.
`get_bond_between`(i, j)	Returns the bond between two atoms
`get_positions`()	Copy the positions of the topology into a new array.
`hierarchy_iterator`(iter_name)	Iterate over all molecules with the given hierarchy scheme.
`is_bonded`(i, j)	Returns True if the two atoms are bonded
`is_constrained`(iatom, jatom)	Check if a pair of atoms are marked as constrained.
`molecule`(index)	Returns the molecule with a given index in this Topology.
`molecule_atom_start_index`(molecule)	Returns the index of a molecule's first atom in this topology
`molecule_index`(molecule)	Returns the index of a given molecule in this topology
`nth_degree_neighbors`(n_degrees)	Return canonicalized pairs of atoms whose shortest separation is exactly n bonds.
`particle_index`(particle)	Deprecated since version 0.11.0.
`set_positions`(array)	Set the positions in a topology by copying from a single n×3 array.
`to_bson`()	Return a BSON serialized representation.
`to_dict`()
`to_file`(file[, positions, file_format, ...])	Save coordinates and topology to a PDB file.
`to_json`([indent])	Return a JSON serialized representation.
`to_messagepack`()	Return a MessagePack representation.
`to_openmm`([ensure_unique_atom_names])	Create an OpenMM Topology object.
`to_pickle`()	Return a pickle serialized representation.
`to_toml`()	Return a TOML serialized representation.
`to_xml`([indent])	Return an XML representation.
`to_yaml`()	Return a YAML serialized representation.

Attributes

`amber_impropers`	Iterate over improper torsions in the molecule, but only those with trivalent centers, reporting the central atom first in each improper.
`angles`	iterator over the angles in this Topology.
`aromaticity_model`	Get the aromaticity model applied to all molecules in the topology.
`atoms`	Returns an iterator over the atoms in this Topology.
`bonds`	Returns an iterator over the bonds in this Topology
`box_vectors`	Return the box vectors of the topology, if specified
`constrained_atom_pairs`	Returns the constrained atom pairs of the Topology
`identical_molecule_groups`	Returns groups of chemically identical molecules, identified by index and atom map.
`impropers`	iterator over the possible improper torsions in this Topology.
`is_periodic`	Return whether or not this Topology is intended to be described with periodic boundary conditions.
`molecules`	Returns an iterator over all the Molecules in this Topology
`n_angles`	number of angles in this Topology.
`n_atoms`	Returns the number of atoms in in this Topology.
`n_bonds`	Returns the number of Bonds in in this Topology.
`n_impropers`	number of possible improper torsions in this Topology.
`n_molecules`	Returns the number of molecules in this Topology
`n_particles`	Deprecated since version 0.11.0.
`n_propers`	number of proper torsions in this Topology.
`n_reference_molecules`	Deprecated since version 0.11.0.
`n_topology_atoms`	Deprecated since version 0.11.0.
`n_topology_bonds`	Deprecated since version 0.11.0.
`n_topology_molecules`	Deprecated since version 0.11.0.
`n_topology_particles`	Deprecated since version 0.11.0.
`n_unique_molecules`	Returns the number of unique molecules in this Topology
`particles`	Deprecated since version 0.11.0.
`propers`	iterator over the proper torsions in this Topology.
`reference_molecules`	Deprecated since version 0.11.0.
`smirnoff_impropers`	Iterate over improper torsions in the molecule, but only those with trivalent centers, reporting the central atom second in each improper.
`topology_atoms`	Deprecated since version 0.11.0.
`topology_bonds`	Deprecated since version 0.11.0.
`topology_molecules`	Deprecated since version 0.11.0.
`topology_particles`	Deprecated since version 0.11.0.
`unique_molecules`	Get a list of chemically unique molecules in this Topology.

property unique_molecules: Iterator[Molecule]

Get a list of chemically unique molecules in this Topology.

Molecules are considered unique if they fail an isomorphism check with default values (see Molecule.is_isomorphic_with()). The order of molecules returned by this property is arbitrary.

property n_unique_molecules: int: Returns the number of unique molecules in this Topology

classmethod from_molecules(molecules: Union[Molecule, List[Molecule]])[source]

Create a new Topology object containing one copy of each of the specified molecule(s).

Parameters: molecules (Molecule or iterable of Molecules) – One or more molecules to be added to the Topology
Returns: topology (Topology) – The Topology created from the specified molecule(s)

assert_bonded(atom1, atom2)[source]

Raise an exception if the specified atoms are not bonded in the topology.

Parameters

atom1 (Atom or int) – The atoms or atom topology indices to check to ensure they are bonded
atom2 (Atom or int) – The atoms or atom topology indices to check to ensure they are bonded

property aromaticity_model

Get the aromaticity model applied to all molecules in the topology.

Returns: aromaticity_model (str) – Aromaticity model in use.

property box_vectors

Return the box vectors of the topology, if specified

Returns: box_vectors (unit-wrapped numpy array of shape (3, 3)) – The unit-wrapped box vectors of this topology

property is_periodic: Return whether or not this Topology is intended to be described with periodic boundary conditions.

property constrained_atom_pairs: Dict[Tuple[int], Union[Quantity, bool]]

Returns the constrained atom pairs of the Topology

Returns: constrained_atom_pairs (dict of Tuple[int]: Union[unit.Quantity, bool]) – dictionary of the form {(atom1_topology_index, atom2_topology_index): distance}

property n_molecules: int: Returns the number of molecules in this Topology

property molecules: Generator[Union[Molecule, openff.toolkit.topology._mm_molecule._SimpleMolecule], None, None]

Returns an iterator over all the Molecules in this Topology

Returns: molecules (Iterable of Molecule)

molecule(index)[source]

Returns the molecule with a given index in this Topology.

Returns: molecule (openff.toolkit.topology.Molecule)

property n_atoms: int

Returns the number of atoms in in this Topology.

Returns: n_atoms (int)

property atoms: Generator[Atom, None, None]

Returns an iterator over the atoms in this Topology. These will be in ascending order of topology index.

Returns: atoms (Generator of TopologyAtom)

atom_index(atom)[source]

Returns the index of a given atom in this topology

Parameters: atom (Atom) –
Returns: index (int) – The index of the given atom in this topology
Raises: AtomNotInTopologyError – If the given atom is not in this topology

molecule_index(molecule)[source]

Returns the index of a given molecule in this topology

Parameters: molecule (FrozenMolecule) –
Returns: index (int) – The index of the given molecule in this topology
Raises: MoleculeNotInTopologyError – If the given atom is not in this topology

molecule_atom_start_index(molecule)[source]

Returns the index of a molecule’s first atom in this topology

Parameters: molecule (FrozenMolecule) –
Returns: index (int)

property n_bonds

Returns the number of Bonds in in this Topology.

Returns: n_bonds (int)

property bonds

Returns an iterator over the bonds in this Topology

Returns: bonds (Iterable of Bond)

property n_angles

number of angles in this Topology.

Type: int

property angles

iterator over the angles in this Topology.

Type: Iterable of Tuple[Atom]

property n_propers

number of proper torsions in this Topology.

Type: int

property propers

iterator over the proper torsions in this Topology.

Type: Iterable of Tuple[TopologyAtom]

property n_impropers

number of possible improper torsions in this Topology.

Type: int

property impropers

iterator over the possible improper torsions in this Topology.

Type: Iterable of Tuple[TopologyAtom]

property smirnoff_impropers

Iterate over improper torsions in the molecule, but only those with trivalent centers, reporting the central atom second in each improper.

Note that it’s possible that a trivalent center will not have an improper assigned. This will depend on the force field that is used.

Also note that this will return 6 possible atom orderings around each improper center. In current SMIRNOFF parameterization, three of these six orderings will be used for the actual assignment of the improper term and measurement of the angles. These three orderings capture the three unique angles that could be calculated around the improper center, therefore the sum of these three terms will always return a consistent energy.

For more details on the use of three-fold (‘trefoil’) impropers, see https://openforcefield.github.io/standards/standards/smirnoff/#impropertorsions

Returns: impropers (set of tuple) – An iterator of tuples, each containing the indices of atoms making up a possible improper torsion. The central atom is listed second in each tuple.

See also

impropers, amber_impropers

property amber_impropers

Iterate over improper torsions in the molecule, but only those with trivalent centers, reporting the central atom first in each improper.

Note that it’s possible that a trivalent center will not have an improper assigned. This will depend on the force field that is used.

Also note that this will return 6 possible atom orderings around each improper center. In current AMBER parameterization, one of these six orderings will be used for the actual assignment of the improper term and measurement of the angle. This method does not encode the logic to determine which of the six orderings AMBER would use.

Returns: impropers (set of tuple) – An iterator of tuples, each containing the indices of atoms making up a possible improper torsion. The central atom is listed first in each tuple.

See also

impropers, smirnoff_impropers

nth_degree_neighbors(n_degrees: int)[source]

Return canonicalized pairs of atoms whose shortest separation is exactly n bonds. Only pairs with increasing atom indices are returned.

Parameters: n (int) – The number of bonds separating atoms in each pair
Returns: neighbors (iterator of tuple of Atom) – Tuples (len 2) of atom that are separated by n bonds.

Notes

The criteria used here relies on minimum distances; when there are multiple valid paths between atoms, such as atoms in rings, the shortest path is considered. For example, two atoms in “meta” positions with respect to each other in a benzene are separated by two paths, one length 2 bonds and the other length 4 bonds. This function would consider them to be 2 apart and would not include them if n=4 was passed.

chemical_environment_matches(query, aromaticity_model='MDL', unique=False, toolkit_registry=GLOBAL_TOOLKIT_REGISTRY)[source]

Retrieve all matches for a given chemical environment query.

TODO:

Do we want to generalize this to other kinds of queries too, like mdtraj DSL, pymol selections, atom index slices, etc? We could just call it topology.matches(query)

Parameters

query (str or ChemicalEnvironment) – SMARTS string (with one or more tagged atoms) or ChemicalEnvironment query Query will internally be resolved to SMARTS using query.as_smarts() if it has an .as_smarts method.
aromaticity_model (str) – Override the default aromaticity model for this topology and use the specified aromaticity model instead. Allowed values: [‘MDL’]

Returns

matches (list of Topology._ChemicalEnvironmentMatch) – A list of tuples, containing the topology indices of the matching atoms.

property identical_molecule_groups: Dict[int, List[Tuple[int, Dict[int, int]]]]

Returns groups of chemically identical molecules, identified by index and atom map.

Returns: identical_molecule_groups – A dict of the form {unique_mol_idx : [(topology_mol_idx, atom_map), ...]. Each key is the topology molecule index of the first instance of a unique chemical species. Iterating over the keys will yield all of the unique chemical species in the topology. Each value is a list of all instances of that chemical species in the topology. Each element of the list is a 2-tuple where the first element is the molecule index of the instance, and the second element maps the atom topology indices of the key molecule to the instance. The molecule instance corresponding to the key is included in the list, so the list is a complete list of all instances of that chemical species.

Examples

>>> from openff.toolkit import Molecule, Topology
>>> # Create a water ordered as OHH
>>> water1 = Molecule()
>>> water1.add_atom(8, 0, False)
>>> water1.add_atom(1, 0, False)
>>> water1.add_atom(1, 0, False)
>>> water1.add_bond(0, 1, 1, False)
>>> water1.add_bond(0, 2, 1, False)
...
>>> # Create a different water ordered as HOH
>>> water2 = Molecule()
>>> water2.add_atom(1, 0, False)
>>> water2.add_atom(8, 0, False)
>>> water2.add_atom(1, 0, False)
>>> water2.add_bond(0, 1, 1, False)
>>> water2.add_bond(1, 2, 1, False)
...
>>> top = Topology.from_molecules([water1, water2])
>>> top.identical_molecule_groups
{0: [(0, {0: 0, 1: 1, 2: 2}), (1, {0: 1, 1: 0, 2: 2})]}

classmethod from_dict(topology_dict)[source]

Create a new Topology from a dictionary representation

Parameters: topology_dict (OrderedDict) – A dictionary representation of the topology.
Returns: topology (Topology) – A Topology created from the dictionary representation

classmethod from_openmm(openmm_topology, unique_molecules=None)[source]

Construct an OpenFF Topology object from an OpenMM Topology object.

This method guarantees that the order of atoms in the input OpenMM Topology will be the same as the ordering of atoms in the output OpenFF Topology. However it does not guarantee the order of the bonds will be the same.

Hierarchy schemes are taken from the OpenMM topology, not from unique_molecules.

Parameters

openmm_topology (openmm.app.Topology) – An OpenMM Topology object
unique_molecules (iterable of objects that can be used to construct unique Molecule objects) – All unique molecules must be provided, in any order, though multiple copies of each molecule are allowed. The atomic elements and bond connectivity will be used to match the reference molecules to molecule graphs appearing in the OpenMM Topology. If bond orders are present in the OpenMM Topology, these will be used in matching as well.

Returns

topology (openff.toolkit.topology.Topology) – An OpenFF Topology object

to_openmm(ensure_unique_atom_names: Union[str, bool] = 'residues')[source]

Create an OpenMM Topology object.

The atom metadata fields residue_name, residue_number, insertion_code, and chain_id are used to group atoms into OpenMM residues and chains.

Contiguously-indexed atoms with the same residue_name, residue_number, insertion_code, and chain_id will be put into the same OpenMM residue.

Contiguously-indexed residues with with the same chain_id will be put into the same OpenMM chain.

This method will never make an OpenMM chain or residue larger than the OpenFF Molecule that it came from. In other words, no chain or residue will span two OpenFF Molecules.

This method will not populate the OpenMM Topology with virtual sites.

Parameters

ensure_unique_atom_names –

Whether to generate new atom names to ensure uniqueness within a molecule or hierarchy element.

If the name of a HierarchyScheme is given as a string, new atom names will be generated so that each element of that scheme has unique atom names. Molecules without the given hierarchy scheme will be given unique atom names within that molecule.
If True, new atom names will be generated so that atom names are unique within a molecule.
If False, the existing atom names will be used.

Returns

openmm_topology (openmm.app.Topology) – An OpenMM Topology object

to_file(file: Union[Path, str, TextIO], positions: Optional[Union[OMMQuantity, Quantity, ndarray[Any, dtype[ScalarType]]]] = None, file_format: Literal['PDB'] = 'PDB', keep_ids: bool = False, ensure_unique_atom_names: Union[str, bool] = 'residues')[source]

Save coordinates and topology to a PDB file.

Reference: https://github.com/openforcefield/openff-toolkit/issues/502

Notes:

Atom numbering may not remain same, for example if the atoms in water are numbered as 1001, 1002, 1003, they would change to 1, 2, 3. This doesn’t affect the topology or coordinates or atom-ordering in any way.
Same issue with the amino acid names in the pdb file, they are not returned.

Parameters

file – A file-like object to write to, or a path to save the file to.
positions (Array with shape (n_atoms, 3) and dimensions of length) –
May be a…
- openmm.unit.Quantity object which has atomic positions as a list of unit-tagged Vec3 objects
- openff.units.unit.Quantity object which wraps a numpy.ndarray with dimensions of length
- (unitless) 2D numpy.ndarray, in which it is assumed that the positions are in units of Angstroms.
- None (the default), in which case the first conformer of each molecule in the topology will be used.
file_format – Output file format. Case insensitive. Currently only supported value is "PDB".
keep_ids – If True, keep the residue and chain IDs specified in the Topology rather than generating new ones.
ensure_unique_atom_names –
Whether to generate new atom names to ensure uniqueness within a molecule or hierarchy element.
- If the name of a HierarchyScheme is given as a string, new atom names will be generated so that each element of that scheme has unique atom names. Molecules without the given hierarchy scheme will be given unique atom names within that molecule.
- If True, new atom names will be generated so that atom names are unique within a molecule.
- If False, the existing atom names will be used.
Note that this option cannot guarantee name uniqueness for formats like PDB that truncate long atom names.

get_positions() → Optional[Quantity][source]

Copy the positions of the topology into a new array.

Topology positions are stored as the first conformer of each molecule. If any molecule has no conformers, this method returns None. Note that modifying the returned array will not update the positions in the topology. To change the positions, use Topology.set_positions().

See also

set_positions

set_positions(array: Quantity)[source]

Set the positions in a topology by copying from a single n×3 array.

Note that modifying the original array will not update the positions in the topology; it must be passed again to set_positions().

Parameters: array – Positions for the topology. Should be a unit-wrapped array-like object with shape (n_atoms, 3) and dimensions of length.

See also

get_positions

classmethod from_mdtraj(mdtraj_topology, unique_molecules=None)[source]

Construct an OpenFF Topology object from an MDTraj Topology object.

Parameters

mdtraj_topology (Topology) – An MDTraj Topology object
unique_molecules (iterable of objects that can be used to construct unique Molecule objects) – All unique molecules must be provided, in any order, though multiple copies of each molecule are allowed. The atomic elements and bond connectivity will be used to match the reference molecules to molecule graphs appearing in the MDTraj Topology. If bond orders are present in the MDTraj Topology, these will be used in matching as well.

Returns

topology (openff.toolkit.topology.Topology) – An OpenFF Topology object

get_bond_between(i, j)[source]

Returns the bond between two atoms

Parameters

i (int or TopologyAtom) – Atoms or atom indices to check
j (int or TopologyAtom) – Atoms or atom indices to check

Returns

bond (TopologyBond) – The bond between i and j.

is_bonded(i, j)[source]

Returns True if the two atoms are bonded

Parameters

i (int or TopologyAtom) – Atoms or atom indices to check
j (int or TopologyAtom) – Atoms or atom indices to check

Returns

is_bonded (bool) – True if atoms are bonded, False otherwise.

atom(atom_topology_index)[source]

Get the TopologyAtom at a given Topology atom index.

Parameters: atom_topology_index (int) – The index of the TopologyAtom in this Topology
Returns: An openff.toolkit.topology.TopologyAtom

bond(bond_topology_index)[source]

Get the TopologyBond at a given Topology bond index.

Parameters: bond_topology_index (int) – The index of the TopologyBond in this Topology
Returns: An openff.toolkit.topology.TopologyBond

add_molecule(molecule: Union[Molecule, _SimpleMolecule]) → int[source]: Add a copy of the molecule to the topology

add_constraint(iatom, jatom, distance=True)[source]

Mark a pair of atoms as constrained.

Constraints between atoms that are not bonded (e.g., rigid waters) are permissible.

Parameters

iatom (Atom) – Atoms to mark as constrained These atoms may be bonded or not in the Topology
jatom (Atom) – Atoms to mark as constrained These atoms may be bonded or not in the Topology
distance (unit-wrapped float, optional, default=True) – Constraint distance True if distance has yet to be determined False if constraint is to be removed

is_constrained(iatom, jatom)[source]

Check if a pair of atoms are marked as constrained.

Parameters

iatom (int) – Indices of atoms to mark as constrained.
jatom (int) – Indices of atoms to mark as constrained.

Returns

distance (unit-wrapped float or bool) – True if constrained but constraints have not yet been applied Distance if constraint has already been added to Topology

hierarchy_iterator(iter_name: str) → Iterator[HierarchyElement][source]

Iterate over all molecules with the given hierarchy scheme.

Get an iterator over hierarchy elements from all of the molecules in this topology that provide the appropriately named iterator. This iterator will yield hierarchy elements sorted first by the order that molecules are listed in the Topology, and second by the specific sorting of hierarchy elements defined in each molecule. Molecules without the named iterator are not included.

Parameters: iter_name – The iterator name associated with the HierarchyScheme to retrieve (for example ‘residues’ or ‘chains’)
Returns: iterator of HierarchyElement

property n_topology_atoms: int: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.n_atoms() instead.

property topology_atoms: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.atoms() instead.

property n_topology_bonds: int: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.n_bonds() instead.

property topology_bonds: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.bonds() instead.

property n_topology_particles: int: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.n_particles() instead.

property topology_particles: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.particles() instead.

property reference_molecules: Iterator[Molecule]: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.unique_molecules() instead.

property n_reference_molecules: int: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.n_unique_molecules() instead.

property n_topology_molecules: int: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.n_molecules() instead.

property topology_molecules: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.molecules() instead.

classmethod from_bson(serialized)

Instantiate an object from a BSON serialized representation.

Specification: http://bsonspec.org/

Parameters: serialized (bytes) – A BSON serialized representation of the object
Returns: instance (cls) – An instantiated object

classmethod from_json(serialized: str)

Instantiate an object from a JSON serialized representation.

Specification: https://www.json.org/

Parameters: serialized (str) – A JSON serialized representation of the object
Returns: instance (cls) – An instantiated object

classmethod from_messagepack(serialized)

Instantiate an object from a MessagePack serialized representation.

Specification: https://msgpack.org/index.html

Parameters: serialized (bytes) – A MessagePack-encoded bytes serialized representation
Returns: instance (cls) – Instantiated object.

classmethod from_pickle(serialized)

Instantiate an object from a pickle serialized representation.

Warning

This is not recommended for safe, stable storage since the pickle specification may change between Python versions.

Parameters: serialized (str) – A pickled representation of the object
Returns: instance (cls) – An instantiated object

classmethod from_toml(serialized)

Instantiate an object from a TOML serialized representation.

Specification: https://github.com/toml-lang/toml

Parameters: serlialized (str) – A TOML serialized representation of the object
Returns: instance (cls) – An instantiated object

classmethod from_xml(serialized)

Instantiate an object from an XML serialized representation.

Specification: https://www.w3.org/XML/

Parameters: serialized (bytes) – An XML serialized representation
Returns: instance (cls) – Instantiated object.

classmethod from_yaml(serialized)

Instantiate from a YAML serialized representation.

Specification: http://yaml.org/

Parameters: serialized (str) – A YAML serialized representation of the object
Returns: instance (cls) – Instantiated object

property n_particles: int: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.n_atoms() instead.

to_bson()

Return a BSON serialized representation.

Specification: http://bsonspec.org/

Returns: serialized (bytes) – A BSON serialized representation of the objecft

to_json(indent=None) → str

Return a JSON serialized representation.

Specification: https://www.json.org/

Parameters: indent (int, optional, default=None) – If not None, will pretty-print with specified number of spaces for indentation
Returns: serialized (str) – A JSON serialized representation of the object

to_messagepack()

Return a MessagePack representation.

Specification: https://msgpack.org/index.html

Returns: serialized (bytes) – A MessagePack-encoded bytes serialized representation of the object

to_pickle()

Return a pickle serialized representation.

Warning

This is not recommended for safe, stable storage since the pickle specification may change between Python versions.

Returns: serialized (str) – A pickled representation of the object

to_toml()

Return a TOML serialized representation.

Specification: https://github.com/toml-lang/toml

Returns: serialized (str) – A TOML serialized representation of the object

to_xml(indent=2)

Return an XML representation.

Specification: https://www.w3.org/XML/

Parameters: indent (int, optional, default=2) – If not None, will pretty-print with specified number of spaces for indentation
Returns: serialized (bytes) – A MessagePack-encoded bytes serialized representation.

to_yaml()

Return a YAML serialized representation.

Specification: http://yaml.org/

Returns: serialized (str) – A YAML serialized representation of the object

property particles: Deprecated since version 0.11.0: This property has been deprecated and will soon be removed. Use Topology.atoms() instead.

particle_index(particle) → int[source]: Deprecated since version 0.11.0: This method has been deprecated and will soon be removed. Use Topology.atom_index() instead.