Well, in the mmap case, this is trivially fixed by writing:
```
with open("my_data.pkl", "r+b") as f_in:
    mm = mmap.mmap(f_in.fileno(), 0)

print(pickle.loads(memoryview(mm)))
```

It will also be faster this way, since the pickle will be read directly from memory instead of going through read() calls.

This makes me think that perhaps this issue isn't as bad: it forces people to abandon bad idioms :-)