drop_useless.py

def useless_columns(df):
    """Returns list of columns with less than 30 not null values"""
    columns = []
    for col in df.columns:
        # isnull returns a list-like object with True is an element in the column is NaN and False if element has value
        null_list = pd.isnull(df[col])
        real_values = len([i for i in null_list if i != True])   
        if real_values < 30:
            columns.append(col)
    return columns

super_df.drop(useless_columns(super_df), axis=1, inplace=True)