Examples / exercises encourage anti-patterns in 12-for-loops.md

[augeas]

There are two examples/exercises whose solutions encourage anti-patterns, miss basic Python features introduced previously, and use the language non-idiomatically. We shouldn't add the confusing cognitive load of "Here's an example, but don't do it this way.".

1. Intro to the accumulator pattern:

To be worthwhile, the accumulated values should be somewhat non-trivial, students should not leave the session thinking that a for loop is required to merely sum over an iterable:

sum_to_10 = sum(range(1, 11))

This is a missed opportunity to introduce "sum" in the previous built-in functions section.
Solving the problem of range(10) going from 0-9 would be better solved by explaining that one wanted range(1,11) rather than a superfluous extra addition.
If a cheap-and-cheerful Monte-Carlo simulation to estimate Pi is too much, maybe just count the number of heads in some coin-tosses?

2. Reversing a String:

This is not a good use for a for loop. Slice operators have already been introduced previously, and students should leave thinking that this is how you reverse a string.
reversed_string = 'This is not a palindrome![::-1]

Easy. Yes, this demonstrates that iteratively appending items from a collection will cause them to be in reverse order, but why would anyone do that?

[alee]

Thanks for the feedback! Minor pedantic note that the simplest way to sum to 10 doesn't need the first parameter, sum(range(11)) suffices.

The string reverse slice operator requires a clear explanation to remove it from the realm of magic but I think it would be a great addition to cement the conceptual model of how slicing works in Python.

There are a fair number of things missing from this lesson in its original incarnation that I believe were deliberate design decisions and that I've attempted to honor during my time as a maintainer with the awareness that this scope / vision should evolve over time alongside the instructors and learners using the course...

1. list / dict / set comprehensions
2. lambdas / functions as first class values, example-ridden explanation of call-by-object-reference semantics without the jargon
3. ???

[martinosorb]

There is also a discussion on whether to move conditionals up before for loops. For-loop exercises with conditionals should make much more sense and be more intuitive, imho.