There are a number of text conventions used throughout this book.

CodeInText: Indicates code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles. Here is an example: "The asyncio module provides a number of different transport classes."

A block of code is set as follows:

async def main(url):
    async with aiohttp.ClientSession() as session:
        await download_html(session, url)

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

urls = [
    'http://packtpub.com',
    'http://python.org',
    'http://docs.python.org/3/library/asyncio',
    'http://aiohttp.readthedocs.io',
    'http://google.com'
]

Any command-line input or output is written as follows:

> python3 example5.py
Took 0.72 seconds.

Bold: Indicates a new term, an important word, or words that you see on screen. For example, words in menus or dialog boxes appear in the text like this. Here is an example: "To download the repository, simply click on the Clone or download button in the top-right corner of your window."