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Add abstractmethods to backend classes #7460

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c43c91b
Add abstractmethods to backend classes
Illviljan Jan 19, 2023
1aa5ab0
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jan 19, 2023
d9692f8
See what happens if we remove the set_variable method
TomNicholas Jul 28, 2023
254c65d
Merge branch 'main' into backend_abstractmethods
Illviljan Jul 29, 2023
d82d0c7
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Jul 29, 2023
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37 changes: 20 additions & 17 deletions xarray/backends/common.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@
import os
import time
import traceback
from abc import ABC, abstractmethod
from collections.abc import Iterable
from glob import glob
from typing import TYPE_CHECKING, Any, ClassVar
Expand Down Expand Up @@ -170,17 +171,20 @@ def get_duck_array(self, dtype: np.typing.DTypeLike = None):
return self[key] # type: ignore [index]


class AbstractDataStore:
class AbstractDataStore(ABC):
__slots__ = ()

def get_dimensions(self): # pragma: no cover
raise NotImplementedError()
@abstractmethod
def get_dimensions(self):
...

def get_attrs(self): # pragma: no cover
raise NotImplementedError()
@abstractmethod
def get_attrs(self):
...

def get_variables(self): # pragma: no cover
raise NotImplementedError()
@abstractmethod
def get_variables(self):
...

def get_encoding(self):
return {}
Expand Down Expand Up @@ -300,14 +304,13 @@ def encode_attribute(self, a):
"""encode one attribute"""
return a

def set_dimension(self, dim, length): # pragma: no cover
raise NotImplementedError()
@abstractmethod
def set_dimension(self, dim, length):
...

def set_attribute(self, k, v): # pragma: no cover
raise NotImplementedError()

def set_variable(self, k, v): # pragma: no cover
raise NotImplementedError()
@abstractmethod
def set_attribute(self, k, v):
...

def store_dataset(self, dataset):
"""
Expand Down Expand Up @@ -444,7 +447,7 @@ def encode(self, variables, attributes):
return variables, attributes


class BackendEntrypoint:
class BackendEntrypoint(ABC):
"""
``BackendEntrypoint`` is a class container and it is the main interface
for the backend plugins, see :ref:`RST backend_entrypoint`.
Expand Down Expand Up @@ -485,6 +488,7 @@ def __repr__(self) -> str:
txt += f"\n Learn more at {self.url}"
return txt

@abstractmethod
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@jhamman jhamman Jan 31, 2023

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Per #7437 (comment), we may not want to require all of these methods. We may end up in a situation where BackendEntrypoints must define one or more of open_dataarray, open_dataset, and open_datatree.

cc @jthielen, @keewis

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@TomNicholas TomNicholas Jul 28, 2023

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This seems pretty doable, e.g.

class MyBaseClass:
    def __init__(self):
        super().__init__()

        # Check that at least one of the methods has been overridden
        if all(getattr(self.__class__, m) is getattr(MyBaseClass, m) for m in ['method1', 'method2', 'method3']):
            raise TypeError("You must implement at least one of 'method1', 'method2', 'method3'")

    def method1(self):
        pass

    def method2(self):
        pass

    def method3(self):
        pass

class MyDerivedClass(MyBaseClass):
    def method1(self):
        print("Method1 implemented")

# This will not raise an error
d = MyDerivedClass()

class MyInvalidDerivedClass(MyBaseClass):
    pass

# This will raise a TypeError
i = MyInvalidDerivedClass()
TypeError: You must implement at least one of 'method1', 'method2', 'method3'

def open_dataset(
self,
filename_or_obj: str | os.PathLike[Any] | BufferedIOBase | AbstractDataStore,
Expand All @@ -495,8 +499,7 @@ def open_dataset(
"""
Backend open_dataset method used by Xarray in :py:func:`~xarray.open_dataset`.
"""

raise NotImplementedError
...

def guess_can_open(
self,
Expand Down