def verify_signature(self, signature_filename, data_filename,<EOL>keystore=None):
if not self.gpg:<EOL><INDENT>raise DistlibException('<STR_LIT>'<EOL>'<STR_LIT>')<EOL><DEDENT>cmd = self.get_verify_command(signature_filename, data_filename,<EOL>keystore)<EOL>rc, stdout, stderr = self.run_command(cmd)<EOL>if rc not in (<NUM_LIT:0>, <NUM_LIT:1>):<EOL><INDENT>raise DistlibException('<STR_LIT>'<EOL>'<STR_LIT>' % rc)<EOL><DEDENT>return rc == <NUM_LIT:0><EOL>
Verify a signature for a file.

:param signature_filename: The pathname to the file containing the
                           signature.
:param data_filename: The pathname to the file containing the
                      signed data.
:param keystore: The path to a directory which contains the keys
                 used in verification. If not specified, the
                 instance's ``gpg_home`` attribute is used instead.
:return: True if the signature was verified, else False.