Frustration debugging serial code

[MRAB]

William R. Wing (Bill Wing) wrote:
> 
> 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 terminal window, it fails.
> If the import were failing, wouldn't I get failures on the serial 
> operations?

If the import fails then you wouldn't be able to create a serial object.

> In particular, the ser object is exactly what it should be.  If I print 
> it out, I get
> the same value for ser in either terminal window mode or in the debugger.
> 
> The various status print statements give exactly the expected results in 
> both
> cases.  But when invoked from the terminal window, the X10 controller 
> doesn't
> get commands.
> 
So you can execute:

     stat1 = ser.write('\x02')

but the X10 controller just isn't receiving it? Is stat1 the same in
both cases (ie, working and non-working)?

>>> 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: ')
>>