Missing values in tuple assignment

Jim Garrison jhg at acm.org
Thu Mar 19 17:57:29 CET 2009

Use case: parsing a simple config file line where lines start with a
keyword and have optional arguments.  I want to extract the keyword and
then pass the rest of the line to a function to process it. An obvious
use of split(None,1)

     cmd,args= = line.split(None,1);
     if cmd in self.switch: self.switch[cmd](self,args)
     else: self.errors.append("unrecognized keyword '{0)'".format(cmd))

Here's a test in IDLE:

  >>> a="now is the time"
  >>> x,y=a.split(None,1)
  >>> x
  >>> y
  'is the time'

However, if the optional argument string is missing:

  >>> a="now"
  >>> x,y=a.split(None,1)
  Traceback (most recent call last):
    File "<pyshell#42>", line 1, in <module>
  ValueError: need more than 1 value to unpack

I understand the problem is not with split() but with the assignment
to a tuple.  Is there a way to get the assignment to default the
missing values to None?

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