関連ワード:  python check if a string is null    python check if a string is empty    python check if a string is not null    python check if a string is empty or none    python check if string is null or whitespace    python check if a string is null or empty    python determine if a string is empty    python check if a string is not empty    python check if string is null empty or whitespace    python check if string is empty or whitespace