Python: How to sort a list of dictionaries by several values?

Question

I want to sort a list at first by a value and then by a second value. Is there an easy way to do this? Here is a small example:

A = [{'name':'john','age':45},      {'name':'andi','age':23},      {'name':'john','age':22},      {'name':'paul','age':35},      {'name':'john','age':21}] 

This command is for sorting this list by 'name':

sorted(A, key = lambda user: user['name']) 

But how I can sort this list by a second value? Like 'age' in this example.

I want a sorting like this (first sort by 'name' and then sort by 'age'):

andi - 23 john - 21 john - 22 john - 45 paul - 35 

Thanks!

Answer 1

>>> A = [{'name':'john','age':45},      {'name':'andi','age':23},      {'name':'john','age':22},      {'name':'paul','age':35},      {'name':'john','age':21}] >>> sorted(A, key = lambda user: (user['name'], user['age'])) [{'age': 23, 'name': 'andi'}, {'age': 21, 'name': 'john'}, {'age': 22, 'name': 'john'}, {'age': 45, 'name': 'john'}, {'age': 35, 'name': 'paul'}] 

This sorts by a tuple of the two attributes, the following is equivalent and much faster/cleaner:

>>> from operator import itemgetter >>> sorted(A, key=itemgetter('name', 'age')) [{'age': 23, 'name': 'andi'}, {'age': 21, 'name': 'john'}, {'age': 22, 'name': 'john'}, {'age': 45, 'name': 'john'}, {'age': 35, 'name': 'paul'}] 

From the comments: @Bakuriu

I bet there is not a big difference between the two, but itemgetter avoids a bit of overhead because it extracts the keys and make the tuple during a single opcode(CALL_FUNCTION), while calling the lambda will have to call the function, load the various constants(which are other bytecodes) finally call the subscript (BINARY_SUBSCR), build the tuple and return it... that's a lot more work for the interpreter.

To summarize: itemgetter keeps the execution fully on the C level, so it's as fast as possible.

Answer 2

from operator import itemgetter  sorted(your_list, key=itemgetter('name', 'age'))