Human: check that can open file. Assistant: 
Here is a Python function to check that can open a file

import os

def check_open(filename):
    """
    Check if the file is open
    Returns True if file is open else False
    """
    if os.path.isfile(filename):
        return True
    else:
        return False

# Enter the filename
filename = 'test.txt'

# Calling the function
print((check_open(filename)))

#Example Output
# True

#Remember to inspect code for bugs.