Anaconda needs to link _gdbm

[iabraham]

The shelve module will try to use one of three underlying database implementations: gdbm, ndbm or dumbdbm (see here). When neither gdbm or ndbm is found it falls back to dumbdbm. With dumbdbm implementation, it seems that opening in with the r flag (for read only) seems to have no effect on preventing writes. See this for example. The fix is to use gdbm or ndbm. On MacOS cursory testing shows that ndbm gets used by default (even with Anaconda) whereas on Linux:

• You need to do: sudo apt-get install python3-gdbm to install the module and then
• Manually link the library. See this answer for details.