Repository: Lightning-AI/pytorch-lightning
File: pytorch_lightning/trainer/connectors/optimizer_connector.py (Python)

Code before:
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from typing import Any, Dict, List, Optional

from pytorch_lightning.utilities import rank_zero_warn
from pytorch_lightning.utilities.exceptions import MisconfigurationException


class OptimizerConnector:
    def __init__(self, trainer):
        self.trainer = trainer

    def on_trainer_init(self, enable_pl_optimizer):
        self.trainer._enable_pl_optimizer = enable_pl_optimizer
        self.trainer.lr_schedulers = []
        self.trainer.optimizers = []
        self.trainer.optimizer_frequencies = []

    def update_learning_rates(
        self, interval: str, monitor_metrics: Optional[Dict[str, Any]] = None, opt_indices: List[int] = []
    ):
        """Update learning rates.

        Args:
            interval: either 'epoch' or 'step'.
            monitor_metrics: dict of possible values to monitor
        """
        if not self.trainer.lr_schedulers:
            return

        for scheduler_idx, lr_scheduler in enumerate(self.trainer.lr_schedulers):
            if isinstance(lr_scheduler['opt_idx'], int) and lr_scheduler['opt_idx'] not in opt_indices:
                continue

            current_idx = self.trainer.batch_idx if interval == 'step' else self.trainer.current_epoch
            current_idx += 1  # account for both batch and epoch starts from 0
            # Take step if call to update_learning_rates matches the interval key and
            # the current step modulo the schedulers frequency is zero
            if lr_scheduler['interval'] == interval and current_idx % lr_scheduler['frequency'] == 0:
                # If instance of ReduceLROnPlateau, we need a monitor
                monitor_key, monitor_val = None, None
                if lr_scheduler['reduce_on_plateau']:
                    monitor_key = lr_scheduler['monitor']
                    monitor_val = (
                        monitor_metrics.get(monitor_key)

Review comment (suggestion):
Using a mutable object as the default value is very discouraged: https://docs.python-guide.org/writing/gotchas/#mutable-default-arguments

Use `None` as the default and initialize it to a list at the beginning of the function


Code after:
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
from typing import Any, Dict, List, Optional

from pytorch_lightning.utilities import rank_zero_warn
from pytorch_lightning.utilities.exceptions import MisconfigurationException


class OptimizerConnector:

    def __init__(self, trainer):
        self.trainer = trainer

    def on_trainer_init(self):
        self.trainer.lr_schedulers = []
        self.trainer.optimizers = []
        self.trainer.optimizer_frequencies = []

    def update_learning_rates(
        self, interval: str, monitor_metrics: Optional[Dict[str, Any]] = None, opt_indices: Optional[List[int]] = None
    ):
        """Update learning rates.

        Args:
            interval: either 'epoch' or 'step'.
            monitor_metrics: dict of possible values to monitor
        """
        if not self.trainer.lr_schedulers or not self.trainer.lightning_module.automatic_optimization:
            return

        if opt_indices is None:
            opt_indices = []

        for scheduler_idx, lr_scheduler in enumerate(self.trainer.lr_schedulers):
            if isinstance(lr_scheduler['opt_idx'], int) and lr_scheduler['opt_idx'] not in opt_indices:
                continue

            current_idx = self.trainer.batch_idx if interval == 'step' else self.trainer.current_epoch
            current_idx += 1  # account for both batch and epoch starts from 0
            # Take step if call to update_learning_rates matches the interval key and
            # the current step modulo the schedulers frequency is zero
            if lr_scheduler['interval'] == interval and current_idx % lr_scheduler['frequency'] == 0:
                # If instance of ReduceLROnPlateau, we need a monitor
                monitor_key, monitor_val = None, None
                if lr_scheduler['reduce_on_plateau']: