cloudpipe/cloudpickle

Unable to pickle functions that are decorated with `functools.lru_cache()`

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#178 创建于 2018年6月20日

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 (14 评论) (12 反应) (0 负责人)Python (1,407 star) (152 fork)batch import
bughelp wanted

描述

Observed behavior

The cloudpickle module is unable to pickle functions that are cached via the functools.lru_cache decorator function.

The following minimal example triggers the issue on Python 3.6.5 and cloudpickle version 0.5.3:

# minimal.py
from functools import lru_cache
import cloudpickle

@lru_cache()
def cached_func():
    pass

cloudpickle.dumps(cached_func)

Resulting in the following traceback:

$ python minimal.py
Traceback (most recent call last):
  File "minimal.py", line 8, in <module>
    cloudpickle.dumps(cached_func)
  File "/Users/csadorf/miniconda3/lib/python3.6/site-packages/cloudpickle/cloudpickle.py", line 895, in dumps
    cp.dump(obj)
  File "/Users/csadorf/miniconda3/lib/python3.6/site-packages/cloudpickle/cloudpickle.py", line 268, in dump
    return Pickler.dump(self, obj)
  File "/Users/csadorf/miniconda3/lib/python3.6/pickle.py", line 409, in dump
    self.save(obj)
  File "/Users/csadorf/miniconda3/lib/python3.6/pickle.py", line 507, in save
    self.save_global(obj, rv)
  File "/Users/csadorf/miniconda3/lib/python3.6/site-packages/cloudpickle/cloudpickle.py", line 642, in save_global
    return self.save_dynamic_class(obj)
  File "/Users/csadorf/miniconda3/lib/python3.6/site-packages/cloudpickle/cloudpickle.py", line 497, in save_dynamic_class
    self.save_reduce(tp, (obj.__name__, obj.__bases__, type_kwargs), obj=obj)
AttributeError: 'functools._lru_cache_wrapper' object has no attribute '__bases__'

Versions:

$ python -V
Python 3.6.5 :: Anaconda, Inc.
$ python -c "import cloudpickle; print(cloudpickle.__version__)"
0.5.3

Expected behavior

The cloudpickle module should handle cached functions by either pickling or ignoring the cache or at least should fail with a descriptive error message.

贡献者指南

技术栈
python
领域
data
议题类型
bug
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
1-2 days
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
fresh
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
Pythonpicklecloudpickle codebase
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
55
研究方向
Investigate the cloudpickle.py file, focusing on the save global and save dynamic class methods (lines around 642 and 497). Understand how other function wrappers are handled, such as partial or wraps. The lru cache wrapper should be treated similarly, possibly by extracting the original function or by using a custom reducer. Look at the Python docs for functools.lru cache to understand its wrapper behavior. Also review any existing comments or PRs related to this issue for prior attempts.