def null_count(df): 
    """
    Check a dataframe for nulls and return the number of missing values
    """

    # Example Input (df = pd.DataFrame):
    # > | column 0    | column 1    | column 2    |
    # > | ----------- | ----------- | ----------- |
    # > | NaN         | 9           | 10          |
    # > | 4           | NaN         | 2           |
    # > | 3           | NaN         | 2           |

    # Function:
    # > `null_count(df)`

    # Expected Output (int):
    # > `3`

    # x = [df[col].isna().sum() for col in df.columns]
    # y = 0
    # for num in x:
    #   y += num
    #   return y

    return df.isna().sum().sum()