tijko tijko - 6 months ago 10
Python Question

Sort a list based on dictionary values in python?

Say I have a dictionary and then I have a list that contains the dictionary's keys. Is there a way to sort the list based off of the dictionaries values?

I have been trying this:

trial_dict = {'*':4, '-':2, '+':3, '/':5}
trial_list = ['-','-','+','/','+','-','*']


I went to use:

sorted(trial_list, key=trial_dict.values())


And got:

TypeError: 'list' object is not callable


Then I went to go create a function that could be called with
trial_dict.get()
:

def sort_help(x):
if isinstance(x, dict):
for i in x:
return x[i]

sorted(trial_list, key=trial_dict.get(sort_help(trial_dict)))


I don't think the
sort_help
function is having any affect on the sort though. I'm not sure if using
trial_dict.get()
is the correct way to go about this either.

Answer

Yes dict.get is the correct (or at least, the simplest) way:

sorted(trial_list, key=trial_dict.get)

As Mark Amery commented, the equivalent explicit lambda:

sorted(trial_list, key=lambda x: trial_dict[x])

might be better, for at least two reasons:

  1. the sort expression is visible and immediately editable
  2. it doesn't suppress errors (when the list contains something that is not in the dict).
Comments