Why does (Py)ZeroMQ open so many Unix socket files?

I tried to monitor the number of open Unix socket files with lsof -U | wc -l while I executed this code:

>>> import zmq
# 1375 Unix socket files
>>> c = zmq.Context()
# 1377 Unix socket files
>>> s = c.socket(zmq.PUSH)
# 1383 Unix socket files
>>> s.close()
# 1381 Unix socket files
>>> c.destroy()
# 1375 Unix socket files

Why is that? I would expect a TCP/IPC socket file being opened when I connected the socket, but what about those files before even connecting?

It seems they are all of type "STREAM":

from Why does (Py)ZeroMQ open so many Unix socket files?