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 gdbmthen 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 changeset4fb0b8bc25c52aae8dcb4353e69c1c88999a9a53 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