Human: Python functions to determine existence. Assistant: 
Here is a Python function to determine existence

import os

def _pid_exists(pid):
  """Helper that returns if pid exists."""
  return os.path.exists(pid)

# Enter the pid
pid = '/tmp/test.pid'

# Calling the function
print((_pid_exists(pid)))

#Example Output
# False

#Remember to inspect code for bugs.