[英]Understanding lambda functions in python
I am new to python and I created a script to sort through "show ip accounting" information from a cisco router. 我是python的新手,我创建了一个脚本来对来自Cisco路由器的“显示ip记帐”信息进行排序。 The script reads a file and breaks up every line into a list, then it creates a list of every line. 该脚本读取文件并将每一行分解为一个列表,然后创建每行的列表。 So I end up with a list of lists: 所以我最终得到一个列表列表:
list a = [[192.168.0.1,172.16.0.1,3434,12222424],[192.168.2.1,172.12.0.1,33334,12667896722424]]
I want to be able to sort by the third column or 4th columns of the list within the list. 我希望能够按列表中列表的第三列或第四列进行排序。
I was able to do it using a lambda function, but my question is how to duplicate this using a standard function? 我可以使用lambda函数来做到这一点,但我的问题是如何使用标准函数复制它?
here is my code below: 这是我的代码如下:
from sys import argv
script, option, filename = argv
a=[]
b=[]
def openfile(filename):
file = open(filename)
for line in file:
if not line.startswith(" "):
a.append((line.split()))
return a
def sort(a,num):
b = sorted(a, reverse=True, key=lambda x: int(x[num]))
return b
def top5(b):
print "Source Destination Packets Bytes"
for i in b[:4]:
print i[0]+" "+i[1]+" "+i[2]+" "+i[3]
def main(option):
a = openfile(filename)
if option == "--bytes":
b = sort(a,3)
top5(b)
elif option == "--packets":
b = sort(a,2)
top5(b)
else:
print """
Not a valid switch,
--bytes to sort by bytes
--packets to sort by packets."""
main(option)
So my question is how can I duplicate the lambda function as a standard custom sort function? 所以我的问题是如何将lambda函数复制为标准的自定义排序函数? I am trying to figure out how this works. 我试图弄清楚它是如何工作的。
b = sorted(a, reverse=True, key=lambda x: int(x[num]) )
how can I duplicate the lambda function as a standard custom sort function? 如何将lambda函数复制为标准的自定义排序函数?
Do you mean this: 你的意思是:
def sort(a, num):
def key(x):
return int(x[num])
return sorted(a, reverse=True, key=key)
or perhaps this: 也许这样:
from functools import partial
def key(num, x):
return int(x[num])
def sort(a, num):
return sorted(a, reverse=True, key=partial(key, num))
? ?
Python provides operator.itemgetter for doing this kind of thing: Python提供了operator.itemgetter来做这种事情:
def sort(a, num):
return sorted(a, reverse=True, key=operator.itemgetter(num))
Edit 编辑
As @NPE pointed out, that doesn't convert the key to an int
for sorting. 正如@NPE指出的那样,这不会将键转换为用于排序的int
。 For that, you're best off to stick with a lambda. 为此,您最好坚持使用lambda。
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