The for loop uses the iteration protocol to step through items in the iterable object across which it is iterating. It first fetches an iterator from the iterable by passing the object to iter, and then calls this iterator object’s __next__ method in 3.X on each iteration and catches the StopIteration exception to determine when to stop looping. The method is named next in 2.X, and is run by the next built-in function in both 3.x and 2.X. Any object that supports this model works in a for loop and in all other iteration contexts. For some objects that are their own iterator, the initial iter call is extraneous but harmless.
Both are iteration tools and contexts. List comprehensions are a concise and often efficient way to perform a common for loop task: collecting the results of applying an expression to all items in an iterable object. It’s always possible to translate a list comprehension to a for loop, and part of the list comprehension expression looks like the header of a for loop syntactically.
Iteration contexts in Python include the for loop; list comprehensions; the map built-in function; the in membership test expression; and the built-in functions sorted, sum, any, and all. This category also includes the list and tuple built-ins, string join methods, and sequence assignments, all of which use the iteration protocol (see answer #1) to step across iterable objects one item at a time.
The best way to read lines from a text file today is to not read it explicitly at all: instead, open the file within an iteration context tool such as a for loop or list comprehension, and let the iteration tool automatically scan one line at a time by running the file’s next handler method on each iteration. This approach is generally best in terms of coding simplicity, memory space, and possibly execution speed requirements.
I’ll accept any of the following as correct answers: fear, intimidation, nice red uniforms, a comfy chair, and soft pillows.