Sample scraping Project Gutenberg using Beautiful Soup and requests
Easy stuff

There are a lot of stylistic issues (indentation, spacing between operators, etc.) that violate PEP 8, you can use tools like pylint to find what they are.

Moving on

 r_html = r.text


Do you really need this? You don't save any characters (not that it is always about saving characters) and you use r_html once. I would just get rid of the line.

I would also say the same about:

url = "https://www.gutenberg.org/ebooks/"


Just get rid of it. Also, in this instance in particular I would get rid of it, because when I read it, I believe there might be a way to abstract it. "Maybe let the user change the url, somehow?") There isn't a particularly good way to "abstract" this url out in particular.

Furthermore, it is considered good practice to use format instead of the addition of strings so:

"https://www.gutenberg.org/ebooks/" + str(book_no)


Becomes:

"https://www.gutenberg.org/ebooks/%d" % book_no


This on the other hand:

"C:\\Users\\syed\\Documents\\Gutenberg\\Book"


Seems like it can be abstracted, what if the user wants to change the location? Maybe by default use this location, but allow the user to change it. Create a default argument to "C:\\Users\\syed\\Documents\\Gutenberg\\Book" but give the user the option to specify it.

Same with:

for chunk in g.iter_content(10000):


What is 10000? Maybe make a default argument for this with the value of 10000 and the name of (possibly) chunk_size?