[python-package] drop Python 3.6 support, use dataclasses

python-package/lightgbm/callback.py

@@ -1,10 +1,15 @@
 # coding: utf-8
 """Callbacks library."""
 import collections
+from dataclasses import dataclass
 from functools import partial
-from typing import Any, Callable, Dict, List, Tuple, Union
+from typing import TYPE_CHECKING, Any, Callable, Dict, List, Optional, Tuple, Union
+
+from .basic import Booster, _ConfigAliases, _LGBM_BoosterEvalMethodResultType, _log_info, _log_warning
+
+if TYPE_CHECKING:
+    from .engine import CVBooster
 
-from .basic import _ConfigAliases, _LGBM_BoosterEvalMethodResultType, _log_info, _log_warning
 
 __all__ = [
     'early_stopping',
@@ -39,14 +44,14 @@ def __init__(self, best_iteration: int, best_score: _EvalResultTuple) -> None:
 
 
 # Callback environment used by callbacks
-CallbackEnv = collections.namedtuple(
-    "CallbackEnv",
-    ["model",
-     "params",
-     "iteration",
-     "begin_iteration",
-     "end_iteration",
-     "evaluation_result_list"])
+@dataclass
+class CallbackEnv:
+    model: Union[Booster, "CVBooster"]
+    params: Dict[str, Any]
+    iteration: int
+    begin_iteration: int
+    end_iteration: int
+    evaluation_result_list: Optional[List[_LGBM_BoosterEvalMethodResultType]]
 
 
 def _format_eval_result(value: _EvalResultTuple, show_stdv: bool) -> str:

python-package/lightgbm/dask.py

@@ -7,8 +7,9 @@
 It is based on dask-lightgbm, which was based on dask-xgboost.
 """
 import socket
-from collections import defaultdict, namedtuple
+from collections import defaultdict
 from copy import deepcopy
+from dataclasses import dataclass
 from enum import Enum, auto
 from functools import partial
 from typing import Any, Dict, Iterable, List, Optional, Tuple, Type, Union
@@ -37,7 +38,11 @@
 _DaskPart = Union[np.ndarray, pd_DataFrame, pd_Series, ss.spmatrix]
 _PredictionDtype = Union[Type[np.float32], Type[np.float64], Type[np.int32], Type[np.int64]]
 
-_HostWorkers = namedtuple('_HostWorkers', ['default', 'all'])
+
+@dataclass
+class _HostWorkers:
+    default: str
+    all_workers: List[str]
 
 
 class _DatasetNames(Enum):
@@ -105,9 +110,9 @@ def _group_workers_by_host(worker_addresses: Iterable[str]) -> Dict[str, _HostWo
         if not hostname:
             raise ValueError(f"Could not parse host name from worker address '{address}'")
         if hostname not in host_to_workers:
-            host_to_workers[hostname] = _HostWorkers(default=address, all=[address])
+            host_to_workers[hostname] = _HostWorkers(default=address, all_workers=[address])
         else:
-            host_to_workers[hostname].all.append(address)
+            host_to_workers[hostname].all_workers.append(address)
     return host_to_workers
 
 
@@ -124,7 +129,7 @@ def _assign_open_ports_to_workers(
     """
     host_ports_futures = {}
     for hostname, workers in host_to_workers.items():
-        n_workers_in_host = len(workers.all)
+        n_workers_in_host = len(workers.all_workers)
         host_ports_futures[hostname] = client.submit(
             _find_n_open_ports,
             n=n_workers_in_host,
@@ -135,7 +140,7 @@ def _assign_open_ports_to_workers(
     found_ports = client.gather(host_ports_futures)
     worker_to_port = {}
     for hostname, workers in host_to_workers.items():
-        for worker, port in zip(workers.all, found_ports[hostname]):
+        for worker, port in zip(workers.all_workers, found_ports[hostname]):
             worker_to_port[worker] = port
     return worker_to_port
 

python-package/setup.py

@@ -349,7 +349,7 @@ def run(self) -> None:
           description='LightGBM Python Package',
           long_description=readme,
           long_description_content_type='text/x-rst',
-          python_requires='>=3.6',
+          python_requires='>=3.7',
           install_requires=[
               'wheel',
               'numpy',