Generators are a memory-efficient way of creating iterators in Python. They produce one value at a time and hold the previous state, allowing you to iterate over large datasets without storing them in memory.

The code defines a function read_file that reads a file line by line and uses a generator to yield each line as it's read. The function opens the file using a with statement to ensure it's properly closed when done. When the function is called with a filename as an argument, it returns a generator object. The for loop then iterates over each line returned by the generator and prints it to the console.