Detect if network is idle in Python

I'm kind of wondering if this is the right approach at all. You will have to average over some time and check very often, and you will still have TOCTTOU problems (That is, just at exactly the same time you decide to start your next download segment, the user clicks on something that starts network activity).

A better approach may actually be to simply throttle (to a user-configurable level?) the download bandwidth of your application, so it only downloads at X KB/s. Yes, it will be a bit slower, but it will be much easier to implement, and much easier to understand how it works.

I would recommend using the psutil.network_io_counters module:

Return network I/O statistics as a namedtuple including the following attributes:

• bytes_sent: number of bytes sent
• bytes_recv: number of bytes received
• packets_sent: number of packets sent
• packets_recv: number of packets received
• errin: total number of errors while receiving
• errout: total number of errors while sending
• dropin: total number of incoming packets which were dropped
• dropout: total number of outgoing packets which were dropped (always 0 on OSX and BSD)

If pernic is True return the same information for every network interface installed on the system as a dictionary with network interface names as the keys and the namedtuple described above as the values.

In [1]: import psutil
In [2]: psutil.network_io_counters(pernic=True)
Out[2]:
{'en0': iostat(bytes_sent=143391435L, bytes_recv=1541801914L,
               packets_sent=827983L, packets_recv=1234558L, errin=0L, errout=0L,
               dropin=0L, dropout=0),
 'gif0': iostat(bytes_sent=0L, bytes_recv=0L, packets_sent=0L, packets_recv=0L,
                errin=0L, errout=0L, dropin=0L, dropout=0),
 'lo0': iostat(bytes_sent=6143860L, bytes_recv=6143860L, packets_sent=55671L,
               packets_recv=55671L, errin=0L, errout=0L, dropin=0L, dropout=0),
 'p2p0': iostat(bytes_sent=0L, bytes_recv=0L, packets_sent=0L, packets_recv=0L,
                errin=0L, errout=0L, dropin=0L, dropout=0),
 'stf0': iostat(bytes_sent=0L, bytes_recv=0L, packets_sent=0L, packets_recv=0L,
                errin=0L, errout=0L, dropin=0L, dropout=0)
}

You can keep track of the sent and received bytes on the interface you want to monitor and that will give you information if the network is idle or busy.