deleting a key from a read-only gdbm should be gdbm.error, not KeyError: >>> import gdbm >>> db = gdbm.open("foo","n") # create new >>> db["a"] = "b" >>> db.close() >>> db = gdbm.open("foo","r") # read only >>> db["x"] = "1" Traceback (most recent call last): File "<stdin>", line 1, in <module> gdbm.error: Reader can't store # correct >>> db["a"] 'b' >>> del db["a"] Traceback (most recent call last): File "<stdin>", line 1, in <module> KeyError: 'a' # WRONG! should be the same as above

Same problem with 3.6.4, start with >>> from dbm import gnu as gdbm then the same incorrect behavior

I like this idea. But this is a behavior change so I think it could only be applied to master branch. But there is a problem, except dbm.gnu and dbm.ndbm, we also get dbm.dumb. It already raises a ValueError when deleting a key in readonly mode. Does it need to be changed to raise dbm.dumb.error to achieve consistency?

I think consistency would be nice -- so, yes, `dbm.dumb.error` instead of `ValueError` (or at least a subtype of `dbm.dumb.error`). Thanks!

 New changeset 4fb0b8bc25c52aae8dcb4353e69c1c88999a9a53 by Xiang Zhang in branch 'master': bpo-33106: change dbm key deletion error for readonly file from KeyError to dbm.error (#6295) https://github.com/python/cpython/commit/4fb0b8bc25c52aae8dcb4353e69c1c88999a9a53