Both of the examples you give are far less readable than an equivalent for loop with an if statement. Programmers use comprehensions because there is an understanding that they are more efficient and the compiler/interpreter can better optimize them.
I use comprehensions because they're self-contained. Instead of a loop with a few statements that introduces new variables into the scope, there's a single expression with fewer loose ends. I think using (non-generator) comprehensions for efficiency is usually the wrong reason.
I find the split comprehension more readable than the equivalent for loop. That's mostly because I'm used to that style, of course, but it's also because it's more constrained. Comprehensions have a very limited grammar, but there are multiple ways to write a for loop that builds a list.
They seem less readable to you because this is not what you're used to. While I agree that complex, one-line comprehensions, possibly with more comprehensions nested inside, can be quite unreadable even for experienced developers, I find that the given examples, with clearly separated expression-loop-condition structure, tend to be quite easy to read and understand, even for junior developers.
I’m quite comfortable with list comprehensions, I’ve been writing them for decades. I like them because they are concise, efficient, more clearly tell the compiler/interpreter their intent.
That said, they are almost always harder to understand than an equivalent for loop with an if statement. A list comprehension by its very nature groups a number of actions into a single expression, it’s harder to break up the parts.
Even an experienced developer who sees them all the time and can understand one in a second, would probably take a half second to understand the equivalent for/if statements.
It all depends on how you approach them. If you see comprehensions as a different form of a for loop, I would tend to agree; but if instead you see them as a different form of a map+filter combination, they suddenly become much more clear.
I agree. If you see comprehensions as map+filter, they make more sense, but it's also exactly that reason that makes them more complex.
List comprehensions are basically a watered down gateway drug to functional programming. Everyone who has ever taken a functional programming course loves it (rightly so), and often tries to find places to use it. Comprehensions do quite a bit in a single expression, it's easy to see that inch towards functional programming.
However, junior developers haven't taken a functional programming courses. They learn to program instructions or statements line-by-line. They are told (not entirely accurate) that every clock tick, the processor moves forward one unit at a time. Your mind starts to imagine the processor in that way, executing a line and going on to the next. Do this, then move forward, then do that. This is procedural programming.
A list comprehension doesn't quite fit that model, because it does quite a bit in a single line (generally map + filter, sometimes reduce).
They teach you that units of complexity can generally be broken down line-by-line.
Of course list comprehensions can be formatted to multiple lines, but it is intrinsically something quite different. A list comprehension is not a statement (e.g., var foo = b + 5), it's an expression (['b' if x < 1 for x in y]) and a pretty complex expression at that.
Junior software developers are taught about statements, going line-by-line. They aren't taught about functional programming or complex expressions. I love python comprehensions, but I wish they were presented in a way that was as easy to understand as a for loop with an if statement.
Senior developers wouldn't care, but it would open up a giant world to junior devs.
What's the difference between a for-loop with an if-statement in it and the comprehension above? Even syntactically, they are almost perfectly matched on tokens. Except with a comprehension, you immediately know that not only it consumes a sequence, but it also produces one (whereas a loop could really do anything).
See my other answer to a similar question above, but basically for-loops and comprehensions are different due to their "learn-ability" and "read-ability". For-loops are easy for novice programmers to understand and functionality is broken up line-by-line as the processor consumes instructions. Comprehensions are an expression, and do several things in a single line. Novice programmers don't understand them, and I do believe that even for expert developers, they are harder to read than an equivalent for-if loop.
