python递归小疑惑

代码如下：

def crawlAndGet(keyword, n):
    if n>0:
        jsondata = os.system('scrapy crawl beijing -a store_dir="./webserver/img" -a keyword="'+keyword+'"')
        if jsondata is not None and jsondata != 0:
            return jsondata
        else:
            return crawlAndGet(keyword,n-1)
    if n<=0:
        return [{'data':'null'}]

def checkCompany(keyword = None):
    conn = MySQLdb.connect(host="localhost", user="root", passwd="", db='qixin', port=3306, charset="utf8")
    cursor = conn.cursor()
    sql="select identify_id,name,ctype,owner,capital,date_found,address,date_from,date_to,scope,reg_auth,date_check,reg_status from qx_company where name = '"+keyword+"'"
    cursor.execute(sql)
    row = cursor.fetchone()
    if row is None:
        return crawlAndGet(keyword, 10)
    else:
        obj = [{'identify_id': row[0].encode("utf-8")},{'name': row[1].encode("utf-8")}, {'ctype': row[2].encode("utf-8")}, {'owner': row[3].encode("utf-8")}, 
{'capital': row[4].encode("utf-8")}, {'date_found': row[5].encode("utf-8")}, {'address': row[6].encode("utf-8")}, 
{'date_from': row[7].encode("utf-8")}, {'date_to': row[8].encode("utf-8")}, {'scope': row[9].encode("utf-8")}, {'reg_auth': row[10].encode("utf-8")}, 
{'date_check': row[11].encode("utf-8")}, {'reg_status': row[12].encode("utf-8")}]
        return json.dumps(obj)
    cursor.close()

if __name__ == '__main__':
    print checkCompany('北京正元商贸有限公司')

在执行checkCompany里的递归函数crawlAndGet是，本以为jsondata有值的时候就会return，发现其实他并没有return直到n<=0时。原因其实时，return jsondata只是代表crawlAndGet(keyword, n-i)执行完了，还要继续往下走。

为了测试这个原理，修改成如下代码：

def crawlAndGet(keyword):
    jsondata = os.system('scrapy crawl beijing -a store_dir="./webserver/img" -a keyword="'+keyword+'"')
    if jsondata is not None and jsondata != 0:
        return jsondata
    else :
        return None

def checkCompany(keyword = None):
    conn = MySQLdb.connect(host="localhost", user="root", passwd="", db='qixin', port=3306, charset="utf8")
    cursor = conn.cursor()
    sql="select identify_id,name,ctype,owner,capital,date_found,address,date_from,date_to,scope,reg_auth,date_check,reg_status from qx_company where name = '"+keyword+"'"
    cursor.execute(sql)
    row = cursor.fetchone()
    if row is None:
        data = crawlAndGet(keyword)
        if data is None:
            data1 = crawlAndGet(keyword)
        else:
            return data
        if data1 is None:
            data2 = crawlAndGet(keyword)
        else:
            return data1
        if data2 is None:
            data3 = crawlAndGet(keyword)
        else:
            return data3
        if data3 is None:
            data4 = crawlAndGet(keyword)
        else:
            return data4
    else:
        obj = [{'identify_id': row[0].encode("utf-8")},{'name': row[1].encode("utf-8")}]
        return json.dumps(obj)
    cursor.close()

if __name__ == '__main__':
    print checkCompany('北京正元商贸有限公司')

发现即使data1，data2有return数据了，他还是会直接执行到return data4之后才返回，奇怪。