examples: python bindings

* 2 more scripts for planned expansion of the HOWTO.
* export-key.py - is very similar to both the import-key.py script and
  an earlier example.
* export-secret-key.py - the holiest of holies, a script to be very
  careful with (though on posix systems it is saved in a chmodded 600
  file).

lang/python/examples/howto/export-key.py

@@ -0,0 +1,71 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+from __future__ import absolute_import, division, unicode_literals
+
+# Copyright (C) 2018 Ben McGinnes <ben@gnupg.org>
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 2 of the License, or (at your option) any later
+# version.
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the Free
+# Software Foundation; either version 2.1 of the License, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU General Public License and the GNU
+# Lesser General Public Licensefor more details.
+#
+# You should have received a copy of the GNU General Public License and the GNU
+# Lesser General Public along with this program; if not, see
+# <http://www.gnu.org/licenses/>.
+
+import gpg
+import os
+import os.path
+import sys
+
+c = gpg.Context(armor=True)
+k = gpg.Data()
+
+print("""
+This script exports a secret key to a file.
+""")
+
+if len(sys.argv) > 3:
+    filepth = sys.argv[1]
+    homedir = sys.argv[2]
+    keytext = sys.argv[3]
+elif len(sys.argv) == 3:
+    filepth = sys.argv[1]
+    homedir = sys.argv[2]
+    keytext = input("Enter the user or key ID for export: ")
+elif len(sys.argv) == 2:
+    filepth = sys.argv[1]
+    homedir = input("Enter the GPG configuration directory path (optional): ")
+    keytext = input("Enter the user or key ID for export: ")
+else:
+    filepth = input("Enter the filename and path of the key file: ")
+    homedir = input("Enter the GPG configuration directory path (optional): ")
+    keytext = input("Enter the user or key ID for export: ")
+
+if homedir.startswith("~"):
+    if os.path.exists(os.path.expanduser(homedir)) is True:
+        c.home_dir = os.path.expanduser(homedir)
+    else:
+        pass
+elif os.path.exists(homedir) is True:
+    c.home_dir = homedir
+else:
+    pass
+
+c.op_export(keytext, 0, k)
+k.seek(0, os.SEEK_SET)
+expkey = k.read()
+
+with open(filepth, "wb") as f:
+    f.write(expkey)

lang/python/examples/howto/export-secret-key.py

@@ -0,0 +1,75 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+from __future__ import absolute_import, division, unicode_literals
+
+# Copyright (C) 2018 Ben McGinnes <ben@gnupg.org>
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 2 of the License, or (at your option) any later
+# version.
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU Lesser General Public License as published by the Free
+# Software Foundation; either version 2.1 of the License, or (at your option)
+# any later version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU General Public License and the GNU
+# Lesser General Public Licensefor more details.
+#
+# You should have received a copy of the GNU General Public License and the GNU
+# Lesser General Public along with this program; if not, see
+# <http://www.gnu.org/licenses/>.
+
+import gpg
+import os
+import os.path
+import sys
+
+c = gpg.Context(armor=True)
+k = gpg.Data()
+
+print("""
+This script exports a secret key to a file.
+
+Will prompt for passphrase using gpg-agent and pinentry.
+""")
+
+if len(sys.argv) > 3:
+    filepth = sys.argv[1]
+    homedir = sys.argv[2]
+    keytext = sys.argv[3]
+elif len(sys.argv) == 3:
+    filepth = sys.argv[1]
+    homedir = sys.argv[2]
+    keytext = input("Enter the user or key ID for export: ")
+elif len(sys.argv) == 2:
+    filepth = sys.argv[1]
+    homedir = input("Enter the GPG configuration directory path (optional): ")
+    keytext = input("Enter the user or key ID for export: ")
+else:
+    filepth = input("Enter the filename and path of the key file: ")
+    homedir = input("Enter the GPG configuration directory path (optional): ")
+    keytext = input("Enter the user or key ID for export: ")
+
+if homedir.startswith("~"):
+    if os.path.exists(os.path.expanduser(homedir)) is True:
+        c.home_dir = os.path.expanduser(homedir)
+    else:
+        pass
+elif os.path.exists(homedir) is True:
+    c.home_dir = homedir
+else:
+    pass
+
+c.op_export(keytext, gpg.core.gpgme.GPGME_EXPORT_MODE_SECRET, k)
+k.seek(0, os.SEEK_SET)
+seckey = k.read()
+
+with open(filepth, "wb") as f:
+    f.write(seckey)
+
+os.chmod(filepth, 0o600)