<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def fingerprint(self):
 """Returns a fingerprint for the identity of the task. A task fingerprint is composed of the options the task is currently running under. Useful for invalidating unchanging targets being executed beneath changing task options that affect outputted artifacts. A task's fingerprint is only valid after the task has been fully initialized. """

    hasher = sha1()
    hasher.update(self.stable_name().encode('utf-8'))
    hasher.update(self._options_fingerprint(self.options_scope).encode('utf-8'))
    hasher.update(self.implementation_version_str().encode('utf-8'))
    for dep in self.subsystem_closure_iter():
      hasher.update(self._options_fingerprint(dep.options_scope).encode('utf-8'))
    return hasher.hexdigest() if PY3 else hasher.hexdigest().decode('utf-8')