Source code for webtraversallibrary.processtools

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# to you under the Apache License, Version 2.0 (the
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# with the License.  You may obtain a copy of the License at

#   http://www.apache.org/licenses/LICENSE-2.0

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# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
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"""
Module collecting helper functions for common processing tasks, such as muting stdout within a context.
"""

import logging
import signal

logger = logging.getLogger("wtl")


class cached_property:
    """
    Decorator that caches a property return value and will return it on later calls.
    Adapted from The Python Cookbok, 2nd edition.

    .. note::
        If you want to map different arguments to values, use `functools.lru_cache`!
    """

    def __init__(self, method):
        self.method = method
        self.name = method.__name__
        self.__doc__ = method.__doc__

    def __get__(self, inst, cls):
        if inst is None:
            return self
        result = self.method(inst)
        object.__setattr__(inst, self.name, result)
        return result


class TimeoutContext:
    """
    Uses :mod:`signal` to raise TimeoutError within the block, if execution went over a specified timeout.
    """

    def __init__(self, n_seconds, error_class=TimeoutError):
        self.n_seconds = n_seconds
        self.error_cls = error_class

    def __enter__(self):
        if self.n_seconds > 0:
            signal.signal(signal.SIGALRM, self.raise_error)
            signal.alarm(self.n_seconds)
            logger.debug(f"TimeoutContext: Operation timeout is set to {self.n_seconds} sec.")

    def __exit__(self, *args, **kwargs):
        # Cancel the alarm
        if self.n_seconds > 0:
            signal.signal(signal.SIGALRM, signal.SIG_DFL)
            time_left = signal.alarm(0)
            if time_left > 0:
                logger.debug(f"TimeoutContext: Operation finished without triggering the alarm ({time_left} sec. left)")
            else:
                logger.debug("TimeoutContext: Operation was interrupted by the timeout")

    def raise_error(self, signal_num, _):
        assert signal_num == signal.SIGALRM
        raise self.error_cls(f"Operation timed out after {self.n_seconds} sec.")