[Tutor] Need help printing a pickled data

[Steven D'Aprano]

On 26/06/13 04:30, Matt D wrote:
> On 06/25/2013 01:54 PM, Alan Gauld wrote:
>> On 25/06/13 17:32, Matt D wrote:
>>
>>>           self.data = data
>>>           with open('mypicklelog.txt','ab') as log: # open in binary mode
>>>               pickle.dump(self.data, log) # serialize data and write to
>>> file
>>>
>>>
>>> And I still get nothing.
>>
>> Define 'nothing'.
>>
>> Does the file exist?
>> Does it have anything in it?
>> Does self.data exist - what does it look like if you print it?
>> Are there any error messages?
>>
> Yeh nothing as in an empty file.  The file is there but there is nothing
> written in it.  self.data exists.  that the problem if have is printing
> what is in it so i dont know what it looks like. No error messages
> currently in the terminal.

The obvious test is to confirm that you can see other output written to the log file.

         self.data = data
         with open('mypicklelog.txt','ab') as log: # open in binary mode
             log.write('before\n')
             pickle.dump(self.data, log)
             log.write('after\n')


I still think it is silly to write pickled data to a log. Logs are for human-readable information, not arbitrary data. Even with text-mode pickle, it's still junk:

py> import pickle
py> data = {'a': None, 'b': 42}
py> pickle.dumps(data, 0)
"(dp0\nS'a'\np1\nNsS'b'\np2\nI42\ns."


Why do you want to see rubbish like that inside your log file? Surely something like this is better?

log.write("data = %r" % data)

which will give you a line like this:

data = {'a': None, 'b': 42}


in your log, which is a million times more understandable than a pickle.


-- 
Steven