selectiontools

This module implements tools for defining subsets of Node and Element objects of large HydPy projects, called “selections”.

Module selectiontools implements the following members:

• Selections Collection class for Selection objects.

• Selection Handles and modifies combinations of Node and Element objects.

---

class hydpy.core.selectiontools.Selections(*selections: Selection)

Bases: object

Collection class for Selection objects.

You can pass an arbitrary number of Selection objects to the constructor of class Selections:

>>> sel1 = Selection("sel1", ["node1", "node2"], ["element1"])
>>> sel2 = Selection("sel2", ["node1", "node3"], ["element2"])
>>> selections = Selections(sel1, sel2)
>>> selections
Selections("sel1", "sel2")

Also, you can query, add, and remove Selection objects via attribute access:

>>> selections.sel3
Traceback (most recent call last):
...
AttributeError: The actual Selections object handles neither a normal attribute nor a Selection object called `sel3` that could be returned.
>>> sel3 = Selection("sel3", ["node1", "node4"], ["element3"])
>>> selections.sel3 = sel3
>>> selections.sel3
Selection("sel3",
          nodes=("node1", "node4"),
          elements="element3")
>>> "sel3" in dir(selections)
True
>>> del selections.sel3
>>> "sel3" in dir(selections)
False
>>> del selections.sel3
Traceback (most recent call last):
...
AttributeError: The actual Selections object handles neither a normal attribute nor a Selection object called `sel3` that could be deleted.

Attribute names must be consistent with the name attribute of the respective Selection object:

>>> selections.sel4 = sel3
Traceback (most recent call last):
...
ValueError: To avoid inconsistencies when handling Selection objects as attributes of a Selections object, attribute name and Selection name must be identical.  However,  for selection `sel3` the given attribute name is `sel4`.

You can use item access alternatively:

>>> selections["sel4"]
Traceback (most recent call last):
...
KeyError: 'The actual Selections object does not handle a Selection object called `sel4` that could be returned.'
>>> selections["sel4"] = Selection("sel4")
>>> selections["sel4"]
Selection("sel4",
          nodes=(),
          elements=())
>>> del selections["sel4"]
>>> del selections["sel4"]
Traceback (most recent call last):
...
KeyError: 'The actual Selections object does not handle a Selection object called `sel4` that could be deleted.'

You can ask for the existence of specific Selection objects within a Selections object both via its name and via the object itself:

>>> sel1 in selections
True
>>> "sel1" in selections
True
>>> sel3 in selections
False
>>> "sel3" in selections
False

Class Selections supports both the iter() and len() operators:

>>> for selection in selections:
...     print(selection.name)
sel1
sel2
>>> len(selections)
2

For convenience, use the “+”, “-”, “+=”, and “-=” operators to compare and modify Selections objects either based on single Selection objects or collections of Selection objects:

>>> larger = selections + sel3
>>> smaller = selections - sel2
>>> sorted(selections.names)
['sel1', 'sel2']
>>> sorted(larger.names)
['sel1', 'sel2', 'sel3']
>>> smaller.names
('sel1',)

>>> smaller += larger
>>> sorted(smaller.names)
['sel1', 'sel2', 'sel3']
>>> smaller -= sel1, sel2
>>> smaller.names
('sel3',)

Note that trying to remove non-existing Selection objects does not raise errors:

>>> smaller -= sel2
>>> smaller.names
('sel3',)
>>> smaller - (sel1, sel2, sel3)
Selections()

The binary operators do not support other types than the mentioned ones:

>>> smaller -= "sel3"
Traceback (most recent call last):
...
TypeError: Binary operations on Selections objects are defined for other Selections objects, single Selection objects, or iterables containing `Selection` objects, but the type of the given argument is `str`.
>>> smaller -= 1   
Traceback (most recent call last):
...
TypeError: ... is `int`.

Use the “==” operator to compare two Selections objects:

>>> larger == smaller
False
>>> larger == (smaller + selections)
True
>>> larger == (sel1, sel2, sel3)
False

property names: Tuple[str, ...]

The names of the actual Selection objects.

>>> from hydpy import Selection, Selections
>>> selections = Selections(
...     Selection("sel1", ["node1", "node2"], ["element1"]),
...     Selection("sel2", ["node1", "node3"], ["element2"]))
>>> sorted(selections.names)
['sel1', 'sel2']

property nodes: Nodes

The Node objects of all handled Selection objects.

>>> from hydpy import Selection, Selections
>>> selections = Selections(
...     Selection("sel1", ["node1", "node2"], ["element1"]),
...     Selection("sel2", ["node1", "node3"], ["element2"]))
>>> selections.nodes
Nodes("node1", "node2", "node3")

property elements: Elements

The Element objects of all handled Selection objects.

>>> from hydpy import Selection, Selections
>>> selections = Selections(
...     Selection("sel1", ["node1"], ["element1"]),
...     Selection("sel2", ["node1"], ["element2", "element3"]))
>>> selections.elements
Elements("element1", "element2", "element3")

add_selections(*selections: Selection) → None

Add the given Selection object(s) to the current Selections object.

>>> from hydpy import Selection, Selections
>>> selections = Selections(Selection("sel1", ["node1"], ["element1"]))
>>> selections.add_selections(
...     Selection("sel2", ["node1"], ["element2", "element3"]),
...     Selection("sel3", ["node2"], []))
>>> selections
Selections("sel1", "sel2", "sel3")
>>> selections.nodes
Nodes("node1", "node2")
>>> selections.elements
Elements("element1", "element2", "element3")

remove_selections(*selections: Selection) → None

Remove the given Selection object(s) from the current Selections object.

>>> from hydpy import Selection, Selections
>>> selections = Selections(
...     Selection("sel1", ["node1"], ["element1"]),
...     Selection("sel2", ["node1"], ["element2", "element3"]))
>>> selections.remove_selections(
...     Selection("sel3", ["node2"], []), selections["sel1"])
>>> selections
Selections("sel2")
>>> selections.nodes
Nodes("node1")
>>> selections.elements
Elements("element2", "element3")

find(device: TypeDevice) → Selections

Return all Selection objects containing the given Node or Element object.

>>> from hydpy import Elements, Nodes, Selection, Selections
>>> nodes = Nodes("n1", "n2", "n3")
>>> elements = Elements("e1", "e2")
>>> selections = Selections(
...     Selection("s1", ["n1", "n2"], ["e1"]),
...     Selection("s2", ["n1"]))
>>> selections.find(nodes.n1)
Selections("s1", "s2")
>>> selections.find(nodes.n2)
Selections("s1")
>>> selections.find(nodes.n3)
Selections()
>>> selections.find(elements.e1)
Selections("s1")
>>> selections.find(elements.e2)
Selections()

query_intersections(selection2element: bool = True) → Dict[Selection, Dict[Selection, Elements]] | Dict[Element, Selections]

A dictionary covering all cases where one Element object is a member of multiple Selection objects.

The dictionary’s structure depends on the value of the optional argument selection2element. See method print_intersections() for an example.

print_intersections(selection2element: bool = True) → None

Print the result of method query_intersections().

We use method print_intersections() to check if any combination of the following selections handles the same elements.

>>> from hydpy import Selection, Selections
>>> selections = Selections(
...     Selection("s1", nodes="n1",elements=("e1", "e2", "e3")),
...     Selection("s2", nodes="n1", elements=("e2", "e3", "e4")),
...     Selection("s3", nodes="n1", elements="e3"),
...     Selection("s4", nodes="n1", elements=("e5", "e6")),
... )

If we call method print_intersections() with argument selection2element True, we find out which selection intersects with which other and which elements are affected:

>>> selections.print_intersections()
selection s1 intersects with...
   ...selection s2 due to the following elements: e2 and e3
   ...selection s3 due to the following elements: e3
selection s2 intersects with...
   ...selection s1 due to the following elements: e2 and e3
   ...selection s3 due to the following elements: e3
selection s3 intersects with...
   ...selection s1 due to the following elements: e3
   ...selection s2 due to the following elements: e3

If we call method print_intersections() with argument selection2element False, we find out which element occurs multiple times in which selections:

>>> selections.print_intersections(selection2element=False)
element e2 is a member of multiple selections: s1 and s2
element e3 is a member of multiple selections: s1, s2, and s3

assignrepr(prefix: str = '') → str

Return a repr() string with a prefixed assignment.

class hydpy.core.selectiontools.Selection(name: str, nodes: devicetools.NodesConstrArg = None, elements: devicetools.ElementsConstrArg = None)

Bases: object

Handles and modifies combinations of Node and Element objects.

In HydPy, Node, and Element objects are the fundamental means to structure projects. However, keeping the overview of huge projects involving thousands of nodes and elements requires additional strategies.

One such strategy is to define different instances of class Selection for different aspects of a project. Often, a selection contains all nodes and elements of a certain subcatchment or all elements handling certain model types. Selections can be overlapping, meaning, for example, that an element can be part of a subcatchment selection and of model-type selection at the same time.

Selections can be written to and read from individual network files, as explained in the documentation on class NetworkManager. Read selections are available via the pub module. In most application scripts (e.g. for parameter calibration), one performs different operations on the nodes and elements of the different selections (e.g. change parameter “a” and “b” for models of selection “x” and “y”, respectively). However, class Selection also provides features for creating combinations of Node and Element objects suitable for different tasks, as explained in the documentation of the respective methods. Here we only show its basic usage with the help of the LahnH example project prepared by function prepare_full_example_2():

>>> from hydpy.examples import prepare_full_example_2
>>> _, pub, _ = prepare_full_example_2()

For example, LahnH defines a headwaters selection:

>>> pub.selections.headwaters
Selection("headwaters",
          nodes=("dill", "lahn_1"),
          elements=("land_dill", "land_lahn_1"))

You can compare this selection with other new or already available selections, with “headwaters < complete” returning True meaning that all nodes and elements of the headwater catchments are also part of the entire catchment:

>>> from hydpy import Selection
>>> test = Selection("test",
...                  elements=("land_dill", "land_lahn_1"),
...                  nodes=("dill", "lahn_1"))
>>> pub.selections.headwaters < test
False
>>> pub.selections.headwaters <= test
True
>>> pub.selections.headwaters == test
True
>>> pub.selections.headwaters != test
False
>>> pub.selections.headwaters >= test
True
>>> pub.selections.headwaters > test
False
>>> pub.selections.headwaters < pub.selections.complete
True
>>> pub.selections.headwaters <= pub.selections.complete
True
>>> pub.selections.headwaters == pub.selections.complete
False
>>> pub.selections.headwaters != pub.selections.complete
True
>>> pub.selections.headwaters >= pub.selections.complete
False
>>> pub.selections.headwaters > pub.selections.complete
False

The len() operator returns the total number of handled node and element objects:

>>> len(test)
4

Use the “+=” and “-=” operators to add or remove nodes and elements:

>>> test += pub.selections.complete
>>> len(test)
11
>>> test -= pub.selections.complete
>>> len(test)
0

Passing a wrong argument to the binary operators results in errors like the following:

>>> test += 1
Traceback (most recent call last):
...
AttributeError: While trying to add selection `test` with object `1` of type `int`, the following error occurred: 'int' object has no attribute 'nodes'
>>> test -= pub.selections.complete.nodes.dill
Traceback (most recent call last):
...
AttributeError: While trying to subtract selection `test` with object `dill` of type `Node`, the following error occurred: 'Node' object has no attribute 'nodes'
>>> test < "wrong"
Traceback (most recent call last):
...
AttributeError: While trying to compare selection `test` with object `wrong` of type `str`, the following error occurred: 'str' object has no attribute 'nodes'

But as usual, checking for equality or inequality returns False and True for uncomparable objects:

>>> test == "wrong"
False
>>> test != "wrong"
True

Applying the str function only returns the selection name:

>>> str(test)
'test'

name: str

The selection’s name.

nodes: Nodes

The explicitly handled Node objects (m).

nodes does not necessarily contain all nodes to which the elements in elements are linked.

elements: Elements

The explicitly handled Element objects.

elements does not necessarily contain all nodes to which the elements in nodes are linked.

search_upstream(device: TypeDevice, name: str = 'upstream', inclusive: bool = True) → Selection

Return the network upstream of the given starting point, including the starting point itself.

>>> from hydpy.examples import prepare_full_example_2
>>> hp, pub, _ = prepare_full_example_2()

You can pass both Node and Element objects and, optionally, the name of the newly created Selection object:

>>> test = pub.selections.complete.copy("test")
>>> test.search_upstream(hp.nodes.lahn_2)
Selection("upstream",
          nodes=("dill", "lahn_1", "lahn_2"),
          elements=("land_dill", "land_lahn_1", "land_lahn_2",
                    "stream_dill_lahn_2", "stream_lahn_1_lahn_2"))
>>> test.search_upstream(hp.elements.stream_lahn_1_lahn_2, "UPSTREAM")
Selection("UPSTREAM",
          nodes=("lahn_1", "lahn_2"),
          elements=("land_lahn_1", "stream_lahn_1_lahn_2"))

Method search_upstream() generally selects all Node objects directly connected to any upstream Element object. Set the inclusive argument to False to circumvent this:

>>> test.search_upstream(hp.elements.stream_lahn_1_lahn_2, "UPSTREAM", False)
Selection("UPSTREAM",
          nodes="lahn_1",
          elements=("land_lahn_1", "stream_lahn_1_lahn_2"))

Wrong device specifications result in errors like the following:

>>> test.search_upstream(1)
Traceback (most recent call last):
...
TypeError: While trying to determine an upstream network of selection `test`, the following error occurred: Either a `Node` or an `Element` object is required as the "outlet device", but the given `device` value is of type `int`.

>>> pub.selections.headwaters.search_upstream(hp.nodes.lahn_3)
Traceback (most recent call last):
...
KeyError: "While trying to determine an upstream network of selection `headwaters`, the following error occurred: 'No device named `lahn_3` available.'"

Method select_upstream() restricts the current selection to the one determined with the method search_upstream():

>>> test.select_upstream(hp.nodes.lahn_2)
Selection("test",
          nodes=("dill", "lahn_1", "lahn_2"),
          elements=("land_dill", "land_lahn_1", "land_lahn_2",
                    "stream_dill_lahn_2", "stream_lahn_1_lahn_2"))

On the contrary, the method deselect_upstream() restricts the current selection to all devices not determined by method search_upstream():

>>> complete = pub.selections.complete.deselect_upstream(hp.nodes.lahn_2)
>>> complete
Selection("complete",
          nodes="lahn_3",
          elements=("land_lahn_3", "stream_lahn_2_lahn_3"))

If necessary, include the “outlet device” manually afterwards:

>>> complete.nodes.add_device(hp.nodes.lahn_2)
>>> complete
Selection("complete",
          nodes=("lahn_2", "lahn_3"),
          elements=("land_lahn_3", "stream_lahn_2_lahn_3"))

Method search_downstream() generally selects all Node objects directly connected to any upstream Element object. Set the inclusive argument to False to circumvent this:

>>> from hydpy import Element, Nodes, Selection
>>> nodes = Nodes(
...     "inlet", "outlet1", "outlet2", "input_", "output", "receiver", "sender")
>>> upper = Element("upper",
...                 inlets=nodes.inlet, outlets=(nodes.outlet1, nodes.outlet2),
...                 inputs=nodes.input_, outputs=nodes.output,
...                 receivers=nodes.receiver, senders=nodes.sender)
>>> test = Selection("test", nodes=nodes, elements=upper)
>>> test.search_upstream(nodes.outlet1, inclusive=True)
Selection("upstream",
          nodes=("inlet", "input_", "outlet1", "outlet2", "output",
                 "receiver", "sender"),
          elements="upper")
>>> test.search_upstream(nodes.outlet1, inclusive=False)
Selection("upstream",
          nodes=("inlet", "input_", "outlet1"),
          elements="upper")

select_upstream(device: TypeDevice, inclusive: bool = True) → Selection

Restrict the current selection to the network upstream of the given starting point, including the starting point itself.

See the documentation on method search_upstream() for additional information.

deselect_upstream(device: TypeDevice, inclusive: bool = True) → Selection

Remove the network upstream of the given starting point from the current selection, including the starting point itself.

See the documentation on method search_upstream() for additional information.

search_downstream(device: TypeDevice, name: str = 'downstream', inclusive: bool = True) → Selection

Return the network downstream of the given starting point, including the starting point itself.

>>> from hydpy.examples import prepare_full_example_2
>>> hp, pub, _ = prepare_full_example_2()

You can pass both Node and Element objects and, optionally, the name of the newly created Selection object:

>>> test = pub.selections.complete.copy("test")
>>> test.search_downstream(hp.nodes.lahn_1)
Selection("downstream",
          nodes=("lahn_1", "lahn_2", "lahn_3"),
          elements=("stream_lahn_1_lahn_2", "stream_lahn_2_lahn_3"))
>>> test.search_downstream(hp.elements.land_lahn_1, "DOWNSTREAM")
Selection("DOWNSTREAM",
          nodes=("lahn_1", "lahn_2", "lahn_3"),
          elements=("land_lahn_1", "stream_lahn_1_lahn_2",
                    "stream_lahn_2_lahn_3"))

Wrong device specifications result in errors like the following:

>>> test.search_downstream(1)
Traceback (most recent call last):
...
TypeError: While trying to determine a downstream network of selection `test`, the following error occurred: Either a `Node` or an `Element` object is required as the "inlet device", but the given `device` value is of type `int`.

>>> pub.selections.headwaters.search_downstream(hp.nodes.lahn_3)
Traceback (most recent call last):
...
KeyError: "While trying to determine a downstream network of selection `headwaters`, the following error occurred: 'No device named `lahn_3` available.'"

Method select_downstream() restricts the current selection to the one determined with the method search_upstream():

>>> test.select_downstream(hp.nodes.lahn_1)
Selection("test",
          nodes=("lahn_1", "lahn_2", "lahn_3"),
          elements=("stream_lahn_1_lahn_2", "stream_lahn_2_lahn_3"))

On the contrary, the method deselect_downstream() restricts the current selection to all devices not determined by method search_downstream():

>>> complete = pub.selections.complete.deselect_downstream(
...     hp.nodes.lahn_1)
>>> complete
Selection("complete",
          nodes="dill",
          elements=("land_dill", "land_lahn_1", "land_lahn_2",
                    "land_lahn_3", "stream_dill_lahn_2"))

If necessary, include the “inlet device” manually afterwards:

>>> complete.nodes.add_device(hp.nodes.lahn_1)
>>> complete
Selection("complete",
          nodes=("dill", "lahn_1"),
          elements=("land_dill", "land_lahn_1", "land_lahn_2",
                    "land_lahn_3", "stream_dill_lahn_2"))

Method search_downstream() generally selects all Node objects directly connected to any upstream Element object. Set the inclusive argument to False to circumvent this:

>>> from hydpy import Element, Nodes, Selection
>>> nodes = Nodes(
...     "inlet1", "inlet2", "outlet", "input_", "output", "receiver", "sender")
>>> lower = Element("lower",
...                 inlets=(nodes.inlet1, nodes.inlet2), outlets=nodes.outlet,
...                 inputs=nodes.input_, outputs=nodes.output,
...                 receivers=nodes.receiver, senders=nodes.sender)
>>> test = Selection("test", nodes=nodes, elements=lower)
>>> test.search_downstream(nodes.inlet1, inclusive=True)
Selection("downstream",
          nodes=("inlet1", "inlet2", "input_", "outlet", "output",
                 "receiver", "sender"),
          elements="lower")
>>> test.search_downstream(nodes.inlet1, inclusive=False)
Selection("downstream",
          nodes=("inlet1", "outlet", "output"),
          elements="lower")

select_downstream(device: TypeDevice, inclusive: bool = True) → Selection

Restrict the current selection to the network downstream of the given starting point, including the starting point itself.

See the documentation on method search_downstream() for additional information.

deselect_downstream(device: TypeDevice, inclusive: bool = True) → Selection

Remove the network downstream of the given starting point from the current selection, including the starting point itself.

See the documentation on method search_downstream() for additional information.

search_modeltypes(*models: Model | module | str, name: str = 'modeltypes') → Selection

Return a Selection object containing only the elements currently handling models of the given types.

>>> from hydpy.examples import prepare_full_example_2
>>> hp, pub, _ = prepare_full_example_2()

You can pass both Model objects and names and, as a keyword argument, the name of the newly created Selection object:

>>> test = pub.selections.complete.copy("test")
>>> from hydpy import prepare_model
>>> hland_v1 = prepare_model("hland_v1")

>>> test.search_modeltypes(hland_v1)
Selection("modeltypes",
          nodes=(),
          elements=("land_dill", "land_lahn_1", "land_lahn_2",
                    "land_lahn_3"))
>>> test.search_modeltypes(
...     hland_v1, "musk_classic", "lland_v1", name="MODELTYPES")
Selection("MODELTYPES",
          nodes=(),
          elements=("land_dill", "land_lahn_1", "land_lahn_2",
                    "land_lahn_3", "stream_dill_lahn_2",
                    "stream_lahn_1_lahn_2", "stream_lahn_2_lahn_3"))

Wrong model specifications result in errors like the following:

>>> test.search_modeltypes("wrong")
Traceback (most recent call last):
...
ModuleNotFoundError: While trying to determine the elements of selection `test` handling the model defined by the argument(s) `wrong` of type(s) `str`, the following error occurred: No module named 'hydpy.models.wrong'

Method select_modeltypes() restricts the current selection to the one determined with the method the search_modeltypes():

>>> test.select_modeltypes(hland_v1)
Selection("test",
          nodes=(),
          elements=("land_dill", "land_lahn_1", "land_lahn_2",
                    "land_lahn_3"))

On the contrary, the method deselect_upstream() restricts the current selection to all devices not determined by method the search_upstream():

>>> pub.selections.complete.deselect_modeltypes(hland_v1)
Selection("complete",
          nodes=(),
          elements=("stream_dill_lahn_2", "stream_lahn_1_lahn_2",
                    "stream_lahn_2_lahn_3"))

select_modeltypes(*models: Model | module | str) → Selection

Restrict the current Selection object to all elements containing the given model types (removes all nodes).

See the documentation on method search_modeltypes() for additional information.

deselect_modeltypes(*models: Model | module | str) → Selection

Restrict the current selection to all elements not containing the given model types (removes all nodes).

See the documentation on method search_modeltypes() for additional information.

search_nodenames(*substrings: str, name: str = 'nodenames') → Selection

Return a new selection containing all nodes of the current selection with a name containing at least one of the given substrings.

>>> from hydpy.examples import prepare_full_example_2
>>> hp, pub, _ = prepare_full_example_2()

Pass the (sub)strings as positional arguments and, optionally, the name of the newly created Selection object as a keyword argument:

>>> test = pub.selections.complete.copy("test")
>>> from hydpy import prepare_model
>>> test.search_nodenames("dill", "lahn_1")
Selection("nodenames",
          nodes=("dill", "lahn_1"),
          elements=())

Wrong string specifications result in errors like the following:

>>> test.search_nodenames(["dill", "lahn_1"])
Traceback (most recent call last):
...
TypeError: While trying to determine the nodes of selection `test` with names containing at least one of the given substrings `['dill', 'lahn_1']`, the following error occurred: 'in <string>' requires string as left operand, not list

Method select_nodenames() restricts the current selection to the one determined with the the method search_nodenames():

>>> test.select_nodenames("dill", "lahn_1")
Selection("test",
          nodes=("dill", "lahn_1"),
          elements=("land_dill", "land_lahn_1", "land_lahn_2",
                    "land_lahn_3", "stream_dill_lahn_2",
                    "stream_lahn_1_lahn_2", "stream_lahn_2_lahn_3"))

On the contrary, the method deselect_nodenames() restricts the current selection to all devices not determined by the method search_nodenames():

>>> pub.selections.complete.deselect_nodenames("dill", "lahn_1")
Selection("complete",
          nodes=("lahn_2", "lahn_3"),
          elements=("land_dill", "land_lahn_1", "land_lahn_2",
                    "land_lahn_3", "stream_dill_lahn_2",
                    "stream_lahn_1_lahn_2", "stream_lahn_2_lahn_3"))

select_nodenames(*substrings: str) → Selection

Restrict the current selection to all nodes with a name containing at least one of the given substrings (does not affect any elements).

See the documentation on method search_nodenames() for additional information.

deselect_nodenames(*substrings: str) → Selection

Restrict the current selection to all nodes with a name not containing at least one of the given substrings (does not affect any elements).

See the documentation on method search_nodenames() for additional information.

search_elementnames(*substrings: str, name: str = 'elementnames') → Selection

Return a new selection containing all elements of the current selection with a name containing at least one of the given substrings.

>>> from hydpy.examples import prepare_full_example_2
>>> hp, pub, _ = prepare_full_example_2()

Pass the (sub)strings as positional arguments and, optionally, the name of the newly created Selection object as a keyword argument:

>>> test = pub.selections.complete.copy("test")
>>> from hydpy import prepare_model
>>> test.search_elementnames("dill", "lahn_1")
Selection("elementnames",
          nodes=(),
          elements=("land_dill", "land_lahn_1", "stream_dill_lahn_2",
                    "stream_lahn_1_lahn_2"))

Wrong string specifications result in errors like the following:

>>> test.search_elementnames(["dill", "lahn_1"])
Traceback (most recent call last):
...
TypeError: While trying to determine the elements of selection `test` with names containing at least one of the given substrings `['dill', 'lahn_1']`, the following error occurred: 'in <string>' requires string as left operand, not list

Method select_elementnames() restricts the current selection to the one determined with the method search_elementnames():

>>> test.select_elementnames("dill", "lahn_1")
Selection("test",
          nodes=("dill", "lahn_1", "lahn_2", "lahn_3"),
          elements=("land_dill", "land_lahn_1", "stream_dill_lahn_2",
                    "stream_lahn_1_lahn_2"))

On the contrary, the method deselect_elementnames() restricts the current selection to all devices not determined by the method search_elementnames():

>>> pub.selections.complete.deselect_elementnames("dill", "lahn_1")
Selection("complete",
          nodes=("dill", "lahn_1", "lahn_2", "lahn_3"),
          elements=("land_lahn_2", "land_lahn_3",
                    "stream_lahn_2_lahn_3"))

select_elementnames(*substrings: str) → Selection

Restrict the current selection to all elements with a name containing at least one of the given substrings (does not affect any nodes).

See the documentation on method search_elementnames() for additional information.

deselect_elementnames(*substrings: str) → Selection

Restrict the current selection to all elements with a name not containing at least one of the given substrings. (does not affect any nodes).

See the documentation on method search_elementnames() for additional information.

copy(name: str) → Selection

Return a new Selection object with the given name and copies of the handled Nodes and Elements objects based on method copy().

add_remotes() → None

Add all remote nodes linked to at least one of the currently handled elements.

One often encounters the situation (for example, after calling method select_upstream()), when a selection does not explicitly include all relevant remote nodes, like in the following example:

>>> from hydpy import Element, Selection
>>> dam = Element("dam", inlets="inflow", outlets="outflow",
...               receivers="discharge_downstream", senders="water_level")
>>> sel = Selection("Dam", elements=dam, nodes=("inflow", "outflow"))
>>> sel
Selection("Dam",
          nodes=("inflow", "outflow"),
          elements="dam")

The method add_remotes() is a small auxiliary function that takes care of this:

>>> sel.add_remotes()
>>> sel
Selection("Dam",
          nodes=("discharge_downstream", "inflow", "outflow",
                 "water_level"),
          elements="dam")

save_networkfile(filepath: str | None = None, write_defaultnodes: bool = True) → None

Save the selection as a network file.

>>> from hydpy.examples import prepare_full_example_2
>>> _, pub, TestIO = prepare_full_example_2()

In most cases, one should conveniently write network files via method save_files() of class NetworkManager. However, using the method save_networkfile() allows for additional configuration via the arguments filepath and write_defaultnodes:

>>> with TestIO():
...     pub.selections.headwaters.save_networkfile()
...     with open("headwaters.py") as networkfile:
...         print(networkfile.read())
# -*- coding: utf-8 -*-

from hydpy import Element, Node


Node("dill", variable="Q",
     keywords="gauge")

Node("lahn_1", variable="Q",
     keywords="gauge")


Element("land_dill",
        outlets="dill",
        keywords="catchment")

Element("land_lahn_1",
        outlets="lahn_1",
        keywords="catchment")

>>> with TestIO():
...     pub.selections.headwaters.save_networkfile(
...         "test.py", write_defaultnodes=False)
...     with open("test.py") as networkfile:
...         print(networkfile.read())
# -*- coding: utf-8 -*-

from hydpy import Element, Node


Element("land_dill",
        outlets="dill",
        keywords="catchment")

Element("land_lahn_1",
        outlets="lahn_1",
        keywords="catchment")

The write_defaultnodes argument does only affect nodes handling the default variable Q:

>>> from hydpy import FusedVariable, Node
>>> from hydpy.inputs import hland_P, hland_T, lland_Nied
>>> from hydpy.outputs import hland_Perc, hland_Q0, hland_Q1
>>> Precip = FusedVariable("Precip", hland_P, lland_Nied)
>>> Runoff = FusedVariable("Runoff", hland_Q0, hland_Q1)
>>> nodes = pub.selections.headwaters.nodes
>>> nodes.add_device(Node("test1", variable="X"))
>>> nodes.add_device(Node("test2", variable=hland_T))
>>> nodes.add_device(Node("test3", variable=Precip))
>>> nodes.add_device(Node("test4", variable=hland_Perc))
>>> nodes.add_device(Node("test5", variable=Runoff))
>>> with TestIO():
...     pub.selections.headwaters.save_networkfile(
...         "test.py", write_defaultnodes=False)
...     with open("test.py") as networkfile:
...         print(networkfile.read())
# -*- coding: utf-8 -*-

from hydpy import Element, FusedVariable, Node
from hydpy.inputs import hland_P, hland_T, lland_Nied
from hydpy.outputs import hland_Perc, hland_Q0, hland_Q1

Precip = FusedVariable("Precip", hland_P, lland_Nied)
Runoff = FusedVariable("Runoff", hland_Q0, hland_Q1)


Node("test1", variable="X")

Node("test2", variable=hland_T)

Node("test3", variable=Precip)

Node("test4", variable=hland_Perc)

Node("test5", variable=Runoff)


Element("land_dill",
        outlets="dill",
        keywords="catchment")

Element("land_lahn_1",
        outlets="lahn_1",
        keywords="catchment")

assignrepr(prefix: str = '') → str

Return a repr() string with a prefixed assignment.