<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def validate_signature(self, filename):
 """Returns True if a valid signature is present for filename"""


        if not GPG_PRESENT:
            return False

        sigfilename = filename + '.sig'

        try:
            with open(sigfilename):
                pass

        except IOError:
            # Signature file does not exist
            return False

        # Check if the sig is valid for the sigfile
        # TODO: Check for whitespace in filepaths
        return verify(sigfilename, filename)