Question: In Scapy (or even just Python, for that sake), how do I get the size in bytes of a given packet?
I'm tempted to use the function `len` but I'm not sure what exactly it returns in the case of packets.

```
>>> len(IP(dst="www.google.com"))
20

>>> len(IP(dst="www.google.com")/TCP(dport=80))
40

```

Answer: 
```
>>> len(IP(dst="www.google.com"))
20

```

There are 20 bytes in a minimal IP header.

```
>>> len(IP(dst="www.google.com")/TCP(dport=80))
40

```

There are another 20 bytes in a minimal TCP header (20+20==40).

So it seems that `len` is returning the packet length.
What I have been observing is that Len(packet[Layer]) will actually perform the action of the LenField type. It will return the number of bytes in the packet, starting with the specified layer, all the way to the end of the packet. So while this method will work for determining the overall packet size, just beware that it will not work to determine the length of an individual layer.