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

[Grant Edwards]

On 2012-06-27, Grant Edwards <invalid at invalid.invalid> wrote:
> On 2012-06-27, Adam <adam at no_thanks.com> wrote:
>> "Grant Edwards" <invalid at invalid.invalid> wrote:

>>> Why do you need to open it a second time?
>>
>> As far as I can tell, the wireless hardware connected to the
>> USB-to-serial converter is receiving data (which may have the serial
>> port open?).  I can see the data being received in TeraTerm (using
>> COM4).  After closing TeraTerm, I start up the Python script and get
>> the following error message ...
[...]
>> Searching for similar encounters of this error message, some people
>> said that calling ser.close() before ser.open() solved the problem.
>> And, it worked for me as well.
>>
>> Is this considered a chicken & egg situation?
>
> Can you post a small example showing what you're doing?

The best way to get help is to write as small a program as possible
that demonstrates the problem, and post it.  I'll help you get
started...

Does this program work?

    import serial
    ser = serial.Serial("COM4")
    ser.close()

At the moment, I don't have access to a Windows machine, but I think
the above should run without any errors.  If it works, then you've
successfully opened and closed the COM4 port.  Start adding
"features", in increments as small as possible, until the program
fails.

Then try to remove stuff that's not needed while still keeping the
failure.

IOW, try to find the smallest possible program that fails.

Usually, in the process of doing that, you'll figure out what you were
doing wrong.  If not, post the smallest failing program you can come
up with, and somebody will be able to help.

If you won't show us what you're doing, we can't tell you what you're
doing wrong.

-- 
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