python - 这句是什么错误？

Question

  File "log1.py", line 140
    for ref, occurnum in nsmallest(10, d.iteritems(), key=lambda (k,v): (-v,k)):
                                                                 ^
SyntaxError: invalid syntax

代码如下

def TopOccurr(num, request, total):
        args = parse_args()
        d = {}
        for i in get_obj[num]:
                if i in d:
                        d[i] = d[i]+1
                else:
                        d[i] = 1
        x = PrettyTable([request, total])
        x.align["Requests"] = "l"
        x.padding_width = 1
        for ref, occurnum in nsmallest(10, d.iteritems(), key=lambda (k,v): (-v,k)):
                x.add_row([ref[:120], occurnum])
        return x.get_string(start=0, end=10, sortby=total, reversesort=True)

py3.5.2

Answer 1

lambda定义的时候，如果有多个参数，那么这些参数是不需要加括号的
e.g.

l=lambda x,y:(y,x) # 正确

l=lambda (x,y):(y,x) # 报错

官方文档中的lambda：

贴上修改后完整代码：

def TopOccurr(num, request, total):
    args = parse_args()
    d = {}
    for i in get_obj[num]:
        if i in d:
            d[i] = d[i]+1
        else:
            d[i] = 1
    x = PrettyTable([request, total])
    x.align["Requests"] = "l"
    x.padding_width = 1
    for ref, occurnum in nsmallest(10, d.iteritems(), key=lambda k,v:(-v,k)):
        x.add_row([ref[:120], occurnum])
    return x.get_string(start=0, end=10, sortby=total, reversesort=True)

实测没有报错（Python 3.6.0，IPython 5.3.0）

Answer 2

python3中lambda不支持用括号的方式解压数据

Answer 3

把参数的括号去掉就行了。