python: Try to be more helpful when given a string to encrypt().

* lang/python/helpers.c (_gpg_obj2gpgme_data_t): Extended error
message.
* lang/python/tests/t-encrypt.py: Test for "encode" in error message.
--
The motivation is to help the user when encrypting fails. I claim that
it is not obvious to not being able to encrypt a string directly.  To
nudge the user into encoding it to bytes, the error message is a bit
extended.

Signed-off-by: Tobias Mueller <[email protected]>

1 files changed, 15 insertions, 0 deletions

diff --git a/lang/python/tests/t-encrypt.py b/lang/python/tests/t-encrypt.py
index 0c0ca357..3cbe8f2f 100755
--- a/lang/python/tests/t-encrypt.py
+++ b/lang/python/tests/t-encrypt.py
@@ -62,3 +62,18 @@ with gpg.Context(armor=True) as c:
         assert support.sign_only.endswith(e.recipients[0].fpr)
     else:
         assert False, "Expected an InvalidRecipients error, got none"
+
+
+
+    try:
+        # People might be tempted to provide strings.
+        # We should raise something useful.
+        ciphertext, _, _ = c.encrypt("Hallo Leute\n",
+                                     recipients=keys,
+                                     sign=False,
+                                     always_trust=True)
+    except TypeError as e:
+        # This test is a bit fragile, because the message
+        # may very well change. So if the behaviour will change
+        # this test can easily be deleted.
+        assert "encode" in str(e)