[Tutor] Converting a String to a Tuple

[Orri Ganel]

Carroll, Barry wrote:

>Greetings:
>
>My UDP client is receiving responses from the server, and now I need to
>process them.  A typical response string looks like this:
>
>    "(0, ''),some data from the test system"
>
>The tuple represents the error code and message.  If the command had failed,
>the response would look like this:
>
>    "(-1, 'Error message from the test system')"
>
>I need to extract the tuple from the rest of the response string.  I can do
>this using eval, like so: 
>
>    errtuple = eval(mytxt[:mytxt.find(')')+1])
>
>Is there another, more specific method for transforming a sting into a
>tuple?
>
>Thanks as always.  
>
>Barry
>
>
>_______________________________________________
>Tutor maillist  -  Tutor at python.org
>http://mail.python.org/mailman/listinfo/tutor
>
>  
>
Well, if you want to avoid eval and are willing to deal with all the 
elements being strings, you could use the following, though it could 
probably be written prettier:

 >>> tstr = "(-1, 'Error message from the test system')"
 >>> tstrt = tuple( tstr[ tstr.find("("):tstr.find(")")+1 ].replace( 
"(","" ).replace( ")","" ).split(", ") )
 >>> tstrt
('-1', "'Error message from the test system'")

Basically, you first get the part of the string between the first set of 
parentheses (so even if there are parentheses afterwards like "(0, '') 
data (specifics of data)", it will still only get the "(0, '')" part), 
then lose the parentheses, split the string along ", " and make the 
string a tuple.  Note that if you use this, you will either have to 
guarantee that the string tuple elements will be separated by a comma 
and a space, or change the above to "....split(","))", in which case 
they will have to be separated by a comma (or you will have a space in 
the element).

HTH,
Orri

P.S. - if you know that the first element will always be an integer and 
that the second will always be a string, you can use the following for 
better results:

 >>> tstrt = 
tuple((int(tstr[tstr.find("("):tstr.find(")")+1].replace("(","").replace(")","").split(", 
")[0]),tstr[tstr.find("("):tstr.find(")")+1].replace("(","").replace(")","").split(", 
")[1][1:-1]))
 >>> tstrt
(-1, 'Error message from the test system')

For a while I tried to come up with some less lengthy lambdas to do the 
job, but that would probably only serve to make it harder to read.

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