import re


def parse_risk(comments: str):
    """Parses tests for key terms indicating high risk. Returns "high risk" if terms are
    found, else returns None. Key terms must not have alphanumeric character before or
    after term"""
    parsed = None
    pattern = "(?<!\w)((risky)|(daytrade)|(small\sposition)|(light\sposition))(?!\w)"
    match = re.search(pattern, comments, flags=re.IGNORECASE)
    if match:
        parsed = "high risk"
    return parsed