No-Op

This function performs a useless computation, since it doesn't return anything or perform a side effect. It's a no-op.

def square(x: int) -> None:
    x * x

This function lacks a return statement but performs a side effect: it changes the value of the y variable that is outside of its scope. It's impure.

y: int = 5

def add_to_y(x: int) -> None:
    global y
    y += x

add_to_y(3)
# y = 8

Even the print function (technically) has a side effect! It doesn't return anything, but it does print text to the console, which is a form of I/O.

Fix the remove_emphasis function by making it pure. remove_emphasis takes a document with any number of lines and removes any number of * characters that are at the start or end of a word. (In case you need it, here's a primer on emphasis in Markdown.)

For example, this:

I *love* Markdown.
I **really love** Markdown.
I ***really really love*** Markdown.

Should become:

I love Markdown.
I really love Markdown.
I really really love Markdown.

1. The problem is that remove_emphasis currently modifies a global variable called doc. It should instead accept a document as an argument and return a new document with emphasis removed.
2. Once you've purified remove_emphasis, you can also delete the global doc variable.

The functions in this assignment use some Python built-ins that are definitely worth knowing:

• str.split – splits a string into a list of substrings based on a separator (by default, whitespace)
• str.strip – removes leading and trailing characters (by default, whitespace) from a string
• map – applies a function to every item of an iterable (like a list) and returns an iterator of the results
• join – combines an iterable of strings into a single string, with a specified separator between them

The syntax of join is simple but can be a bit counterintuitive:

# We call join as a method on the separator, not on the list of strings
" ".join(["I", "love", "Python"])
# "I love Python"