nice radix conversion from int to string

counting matches of '1' is simple, and could easily scale to higher radixes such as octal
could easily be extended to match multiple digits, such as .count('137')

range traversal is clear

accumulator function sum() over a list is also a nice aggregate function

My friend, we write solutions not tests. The TESTS round answers, not solutions. What are you talking about?

For example, if your string contains both 1 and 0, and you replace 1 with I, that might create a situation where another part of the string (e.g., something containing 10) is now altered in an unexpected way when 0 is replaced with O.

What does unstable mean in this context?

very good

It works perfectly for everyone. Not sure where you're getting an error.

Getting all of them can be very expensive for large arrays with small n.

THIS METHORD IS WRONG!
ERROR

condition not met. "Tests round answers to 6 decimal places"

You can return the function atoi's output directly without defining an integer. Nice work. Keep it up

Which means I'm NOT lazy! I knew it this whole time!

Because most people are lazy ;-)

too much code golf and less BP