Frustration debugging serial code

[William R. Wing]

On May 7, 2010, at 2:08 PM, MRAB wrote:

> William R. Wing (Bill Wing) wrote:
>> Hello World -
>> I'm new to both Python and this list, but here's hoping someone can spot my problem.
>> System:  Mac OS-X, 10.6.3 (Intel dual quad processor)
>> Using Python 2.6.1, and pyserial-2.5_rc2-py2.6
>> The following snippet of code is designed to open a port via a KeySpan USB-to-serial converter and communicate with an X10 power line signaling system.  Before you look at the code, let me mention that my frustration is the it executes perfectly if i enter it line by line at the Python prompt, and executes perfectly if I run it under the Wing IDE.  It fails silently (no errors) if I run it as a standalone script.  Clearly, I'm missing something.
> What do you mean "It fails silently"? It might be unable to find the
> modules if you double-click on the script. You could check for that by
> printing a message if the import statement raises an ImportError.

Maybe I should have been more explicit.  The first line in the Python file is:

#!/usr/bin/env Python (alternatively #!/usr/bin/Python - same results either way).

and what I meant was that when I invoke it from a UNIX CLI window, it fails.
If the import were failing, wouldn't I get failures on the serial operations?
In particular, the ser object is exactly what it should be.  If I print it out, I get
the same value for ser from either the UNIX CLI or in the debugger, and in 
both cases it says "open=True"

The various status print statements give exactly the same (expected) results in
both cases.  But when invoked from the terminal window, the X10 controller doesn't
get commands.  If I invoke python from the same window, and enter the script
code interactively one line at a time - it works just fine.


>> TIA,
>> Bill Wing
>> import serial, string
>> port = '/dev/tty.KeySerial1'
>> ser = serial.Serial(port, 9600, timeout=1)   # Set up handle to serial port
>> stat1 = ser.write('\x02')                    # Write "Attention" to PowerLink
>> print(' Stat1 is:', stat1)                   ack = ser.read(2)                            # Check to see if PowerLink is ready
>> if ack == '\x06\r':                          # It returns ACK (\x06) \r if it is
>>    stat2 = ser.write('\x63\x4E\x5C\x45\x41')# send "On" to module at House Code B, device code 2
>>    print(' Stat2 is:', stat2)
>>    stat3 = ser.close()                      # Close serial port
>>    print(' Stat3 is:', stat3)
>> elif ack =='\x15':                           # PowerLink sends NAC (hex 15) if it isn't.
>>    print('Received NAK after first open')
>> else:   print("Something's wrong at 1.\n")
>> dummy = raw_input(' Hit any key to continue: ')
> 
> -- 
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