how to sort lists within list in user defined order?

Question

I want to sort lists of mathematical operators (stored as strings) in order of precedence (*,/,+,-) within a list. There are thousands of lists within my list.

E.g.

my_lists = [['*','+','-'],['-','*','*'],['+','/','-']]

should become:

new_list = [['*','+','-'],['*','*','-'],['/','+','-']]

Is there a way to sort the lists within my list in a user defined order?

Answer 1

You can define the priority with a dictionary, like this

>>> priority = {'*': 0, '/': 1, '+': 2, '-': 3}

and then sort the individual lists, with the value from the priority, like this

>>> [sorted(item, key=priority.get) for item in my_lists]
[['*', '+', '-'], ['*', '*', '-'], ['/', '+', '-']]