Issue with gpg-agent and a python software

[chaica]

Hi,

I'm trying to implement gpg-agent support in a Python software but I've
trouble when my gpg key is not yet stored by the gpg-agent.

I'm using the Python module "os" using os.system() function like this : 

os.system("gpg --use-agent ...")

The output is something like : 
...
[SNIP]
You need a passphrase to unlock the secret key for
user: Foo Lastfoo (Paris, France) <foo at lastfoo.com>"
1024-bit DSA key, ID XXXXXXX, created 2007-09-28

gpg: cancelled by user
gpg: skipped "foo at lastfoo.com": bad passphrase
gpg: [stdin]: clearsign failed: bad passphrase
[SNIP]
...

So signing my text fails. But if I store my passphrase before launching
my software (e.g by signing a file from the command line in the same
shell with gpg), next time I use my software everything works fine. So
it appears it only fails when the passphrase is not stored yet. I
thought my software was going to provide the pinentry window but it is
not the case. And I don't know why.

Bye,
Carl Chenet