Have you ever wondered what happens when you actually send some data over a TCP network connection? To a Python programmer, it looks like you just call one method with some bytes. But in reality, there's so much stuff that gets involved:

• Python hands off the data to the C library.
• The C library hands the data to your kernel.
• The kernel pokes some data into your ethernet card.
• Your ethernet card bounces some electrons off a switch.
• The switch sends those electrons out, possibly all the way to the internet.
• Later, they hit somebody else's ethernet card, which goes through the kernel, which reassembles the data stream, and wakes up a process, and gets read.

I will talk about each of these different steps, how they work, what technology is involved, and, most relevant to your Python programs: how they can fail.