Besides showcasing dictionaries, this use case serves to introduce the Python for loop. The for loop is a simple and efficient way to step through all the items in a sequence
and run a block of code for each item in turn. A user-defined loop variable (key, here) is used to reference the current item each time through. The net effect in our example is to print the unordered dictionary’s keys and values, in sorted-key order. The for loop, and its more general cousin the while loop, are the main ways we code repetitive tasks as statements in our scripts. Really, though, the for loop (like its relative the list comprehension, which we met earlier) is a sequence operation. It works on any object that is a sequence and, like the list comprehension, even on some things that are not. Here, for example, it is stepping across the characters in a string, printing the uppercase version of each as it goes: