PySerial could not open port COM4: [Error 5] Access is denied - please help

[Grant Edwards]

On 2012-06-28, Adam <adam at no_thanks.com> wrote:

> Obviously pySerial considers the serial port open

Because it's already been opened by the Python program.

> and will not open an already open serial port.

Pyserial will happily try if you call the open() of a port that's
already open, but Windows will return an error.

> However, why is it that TeraTerm can open the serial port?

Because TeraTerm only opens it once.

> Here's the link where I read about calling ser.close() before
> ser.open() ...
>
> Trying to open a serial port with pyserial on WinXP -> "Access denied"
>
> http://stackoverflow.com/questions/2063257/trying-to-open-a-serial-port-with-pyserial-on-winxp-access-denied

That code is broken.

The port is opened by this line:

 self.ser=serial.Serial(port='\\.\COM1', baudrate=9600, bytesize=serial.EIGHTBITS, parity=serial.PARITY_NONE, stopbits=serial.STOPBITS_ONE, timeout=1)

And then the author tries to _open_it_a_second_time_ here:

 self.ser.open()
    
> Here's the Python scripts ...
> https://github.com/adafruit/Tweet-a-Watt/downloads
> Click on the "Download as ..." button for the Python scripts

Like I kept telling you, those programs are trying to re-open a port
that they've already open.  Here's the erroneous code:

wattcher.py:

    53  
    54  # open up the FTDI serial port to get data transmitted to xbee
    55  ser = serial.Serial(SERIALPORT, BAUDRATE)
    56  ser.open()
    57  

Line 55 opens the serial port.

Line 56 tries to _open_it_again_.  _The_port_is_already_open_. 
Windows doesn't allow a serial port to be opened twice, therefore the
ser.open() call raises an exception.

Just delete line 56.


The same thing happens here:

gmeter-wattcher.py

    83  
    84  # open up the FTDI serial port to get data transmitted to xbee
    85  ser = serial.Serial(SERIALPORT, BAUDRATE)
    86  ser.open()
    87  

Just delete line 86.
    
See how simple it was to get the problem solved once you posted the
actual code?

-- 
Grant Edwards               grant.b.edwards        Yow! HUMAN REPLICAS are
                                  at               inserted into VATS of
                              gmail.com            NUTRITIONAL YEAST ...