Multi-argument append() is illegal

Guido van Rossum guido at python.org
Mon Feb 28 16:41:02 CET 2000


I've noticed that there is some code out there that creates a list of
tuples and uses code like list.append(a,b,c) to add the tuple (a,b,c)
to the list.  According to the documentation, this is illegal:
append() only takes a single argument, and one should write
list.append((a,b,c)).  However, the actual append() implementation
didn't mind, and implemented list.append(a,b,c) as
list.append((a,b,c)).  Many people are using this even though it's
never been documented.

I am going to rectify this in Python 1.6 -- people coming from other
languages might well expect list.append(a, b, c) to mean the same as
list.append(a); list.append(b); list.append(c), and it's always been
my philosophy to make ambiguous syntax illegal rather than to pick one
interpretation randomly.

This message is simply a heads-up that you should be aware of this
change (when 1.6 comes out, which should be before the summer).  You
can test your programs using the current CVS version (see
www.python.org/download/cvs.html).  You can also grep through your
sources for a pattern like "\. *append *\(.*," -- which doesn't find
every occurrence, but is a good starting point.  If you have a smarter
grep-like tool you may be able to write a tighter matching expression.

Watch out for false hits though: some classes define their own
multi-argument append()...

--Guido van Rossum (home page: http://www.python.org/~guido/)




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