Get greatest key in dictionary but lower than a variable

Question

Given a dictionary and a variable like this:

dic = {0 : 'some', 10 : 'values', 20 : 'whatever'}
var = 14

I want to get the value from the dictionary where the key is the greatest but lower or equal to the variable. I don't know if that's clear but in this case I am looking for 10.

I've come up with this function but I wanted to know if there is an easier way to do it as I am pretty new to python.

def get_greatest_key(dic, var):
    # if the key exists no need to search
    if var in dic:
        return dic[var]
    else:
        # create a list with all the keys sorted in reverse 
        l = sorted(dic, key=dic.get)
        i = 0
        while i < len(l):
            # parse the list
            if l[i] <= var:
                return dic[l[i]]
            i += 1
        # by default we return the last element in the dictionary
        return dic[l[len(l) - 1]]

Answer 1

If you want the maximum key which is less than or equal to var, then you can pass a generator expression to the max function:

>>> dic = {0 : 'some', 10 : 'values', 20 : 'whatever'}
>>> var = 14
>>> max(k for k in dic if k <= var)
10

with corresponding value

>>> dic[max(k for k in dic if k <= var)]
'values'

You can decide what to do with the ValueError thrown if the argument to max is empty as you see fit.