docs: python bindings howto

* Added new advanced section with an example of using the Python
  bindings with CPython code compiled back to C code using Cython.
* Though it may seem a bit counter-intuitive to use the bindings just
  to go back to C via a different route, this is not actually stupid.
* Added examples/howto/advanced/cython/ directory.
* Added keycount.pyx, setup.py and the keycount.c file which the first
  two generated with Cython.  Not including the .so and .o files from
  the build.
* Exported the .texi version of the howto for the main docs.

1 files changed, 16 insertions, 0 deletions

diff --git a/lang/python/examples/howto/advanced/cython/keycount.pyx b/lang/python/examples/howto/advanced/cython/keycount.pyx
new file mode 100755
index 00000000..f0097db2
--- /dev/null
+++ b/lang/python/examples/howto/advanced/cython/keycount.pyx
@@ -0,0 +1,16 @@
+import gpg
+
+c = gpg.Context()
+seckeys = c.keylist(pattern=None, secret=True)
+pubkeys = c.keylist(pattern=None, secret=False)
+
+seclist = list(seckeys)
+secnum = len(seclist)
+
+publist = list(pubkeys)
+pubnum = len(publist)
+
+print("""
+Number of secret keys:  {0}
+Number of public keys:  {1}
+""".format(secnum, pubnum))