我有一个包含字母和数字列表的txt文件，我需要根据数字对它进行排序，我该怎么做？

Question

What I have so far is a program that reads a text file, and puts it into a list. The txt file looks like:

asdf:15.3 eazzz:31.12 qw:1.65 ...

I am kind of new to Python so I'm still trying to figure out how to do this properly. I know this will separate the numbers from the letters, but I don't know where to go from here.

def get_num(str):
    items = str.split(':')
    return float(items[1])

The desired output will have the numbers sorted out in descending order with their respective letters. I know this can probably be done with "sort" but if possible I'd also like to see it done with for-loops.

Answer 1

Don't use str as the input name. To sort a list containing tuples (name, value) just do the following:

sorted(list_name, key = lambda x : x[1], reverse = True)

key = lambda x : x[1] indicates that you want to sort the list by value while reverse = True indicates that you want the sort to be in descending order.

Answer 2

data  = '''asdf:15.3
eazzz:31.12
qw:1.65
adasf:7.3'''

# convert string to list
lst = data.split('\n')

#sort list of data by two things. first the string part second number part
print '\n'.join(sorted(lst, key=lambda item:(item.split(':')[0],float(item.split(':')[1])), reverse = True))

output:

qw:1.65
eazzz:31.12
asdf:15.3
adasf:7.3