You can try something along these lines:
items = root.findall('.//item')
rows = []
for item in items:
row = []
row.extend([item.attrib['client'],item.attrib['is_known']])
for sale in item.findall('.//*'):
row.append(sale.attrib['id'])
rows.append(row)
pd.DataFrame(rows,columns=df_cols)
Output:
client is_known sales1_id sales2_id
0 client_A yes sales1_name sales2_name
1 client_B no sales1_name sales2_name
2 client_C yes sales2_name sales3_name
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…