How to check if a file exists in a directory by sha1?

Question

Python

Hello, tell me how best to implement the script.
It is required that the script writes the sha1 hashes of the files in the directory to txt. At the same time, it checked whether a similar hash was contained (in this case, deleted the file).
Similar methods of checking whether files were present in a directory are welcome to avoid duplicates. Thank you.
Script to write hash of one file to txt:

BUF_SIZE = 65536  # lets read stuff in 64kb chunks!

sha1 = hashlib.sha1()

with open(filename, 'rb') as f:
    while True:
        data = f.read(BUF_SIZE)
        if not data:
            break
        sha1.update(data)

my_file = open("output.txt", "a")
my_file.write('\n' + sha1.hexdigest())
my_file.close()