import hashlib

def calculate_sha1(filepath):
    """
    Calculates the SHA1 hash of a given file.

    Args:
        filepath (str): The path to the file.

    Returns:
        str: The hexadecimal representation of the SHA1 hash, or None if the file is not found.
    """
    sha1_hash = hashlib.sha1()
    try:
        with open(filepath, "rb") as f:
            # Read the file in chunks to handle large files efficiently
            for chunk in iter(lambda: f.read(4096), b""):
                sha1_hash.update(chunk)
        return sha1_hash.hexdigest()
    except FileNotFoundError:
        print(f"Error: File not found at {filepath}")
        return None
    except Exception as e:
        print(f"An error occurred: {e}")
        return None


if __name__ == "__main__":
    # Example usage:
    file_path = "xls.xls"  # Replace with the actual path to your file
    sha1_result = calculate_sha1(file_path)

    if sha1_result:
        print(f"The SHA1 hash of '{file_path}' is: {sha1_result}")