[issue31993] pickle.dump allocates unnecessary temporary bytes / str

[Olivier Grisel]

Olivier Grisel <olivier.grisel at ensta.org> added the comment:

Note that the time difference is not significant. I rerun the last command I got:

```
(py37) ogrisel at ici:~/code/cpython$ python ~/tmp/large_pickle_dump.py --use-pypickle
Allocating source data...
=> peak memory usage: 2.014 GB
Dumping to disk...
done in 4.187s
=> peak memory usage: 2.014 GB
```

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue31993>
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