Python does not close file descriptors

Question

I am developing a long python script that makes many connections with different serial ports. The script will run for several hours in its execution, citing "Too many open files."

I tracked the issue for a serial module, where the .close () method does not seem to reduce the number of file descriptors used by python. I check this with lsof | grep python | wc lsof | grep python | wc lsof | grep python | wc . Using Debian 7.2 and Python 2.7.3

In the example below, more and more file descriptors are slowly being used until it reaches the limit. Why is this and how can I avoid this?

 #!/usr/bin/env python import serial #Used to communicate with pressure controller import logging import time from time import gmtime, strftime logging.basicConfig(filename="open_files_test.log") # Write unusual + significant events to logfile + stdout def log( message ): time = strftime("%Y-%m-%d %H:%M:%S", gmtime()) logging.warning( time + " " + message ) print( message ) for i in range(2000): for n in range(1, 12): try: port_name = "/dev/tty" + str(n+20) com = serial.Serial(port_name,9600,serial.EIGHTBITS,serial.PARITY_NONE,serial.STOPBITS_ONE,0.0,False,False,5.0,False,None) com.open() com.flushInput() com.flushOutput() log("Opened port: " + port_name) except serial.SerialException: com = None log("could not open serial port: " + port_name) com.close() log("Closed port: " + port_name) time.sleep(1) log("Finished Program") 

thanks

Answer 1

Additional com.open causing the problem. According to docs, serial.Serial returns it, so you don't need to open it again. On Linux (all POSIX, as far as I know) open simply increments the counter and closes only decreasing it. Here's a remote answer from @wheaties suggesting using with , which I would recommend:

 with serial.Serial(port_name, 9600, ...) as com: com.flushInput() com.flushOutput() ... 

Answer 2

Use finally to verify that the port is closed.

 try: ... except serial.SerialException: ... finally: com.close()