On my MacOS Mojave 10.14.6 (18G103), after upgrading python to python 3.8, the ctrl-r on the python interpreter does not work.

Here is the working python 3.7 version:
```
$ python3.7 --version 
Python 3.7.3
$ python3.7     
Python 3.7.3 (default, Mar 27 2019, 09:23:15) 
[Clang 10.0.1 (clang-1001.0.46.3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 10
(reverse-i-search)`a': a = 10
``` 
Note that I pressed 'ctrl-r' on my keyboard to bring up the 'reverse-i-search'.

On python3.8, ctrl-r has no response from the interpreter:
```
$ python3.8 --version
Python 3.8.0
$ python3.8          
Python 3.8.0 (v3.8.0:fa919fdf25, Oct 14 2019, 10:23:27) 
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 10
>>> 
```

Interestingly, the ~/.python_history files seems to be updated. Also, when I enter the 'UP' key, the older command comes up. Just that ctrl-r doesn't work.

Here is the output showing that python_history files is being written to:
```
$ rm  ~/.python_history  
$ python3.8               
Python 3.8.0 (v3.8.0:fa919fdf25, Oct 14 2019, 10:23:27) 
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> a = 33
>>> ^D
$ cat  ~/.python_history 
_HiStOrY_V2_
a\040=\04033
```