Understand lambda usage in given python code

Question

On reading through some code, I came across the below snippet which I am not able to understand. Would anyone be able to guide/provide hints/link or a basic explanation of line 3 below

def do_store(*args, **kwargs):
    try:
        key = (args, tuple(sorted(kwargs.items(), key=lambda i:i[0])))
        results = f._results

mainly, what is the following doing?

key=lambda i:i[0]

Answer 1

With the lambda keyword, you create "anonymous functions". They don't have (and don't need to have) a name, because they are immediately assigned (usually) to a callback function.

lambda i:i[0]

is just the body of the function

def f(i):
  return i[0]

The key parameter of the sorted function has to be a function that computes sorting key for a given item. You could also pass the function (name) f as defined above, or use a lambda function for better readability.

As stated in tobias_k's answer, in this piece of code, the whole key parameter is useless.