How to extend a tuple of tuples?

[Ned Batchelder]

On Monday, September 12, 2016 at 4:31:37 PM UTC-4, Thomas 'PointedEars' Lahn wrote:
> Ben Finney wrote:
> > So instead, you want a different tuple. You do that by creating it,
> > explicitly constructing a new sequence with the items you want::
> > 
> >     b = tuple([
> >             item for item in a
> >             ] + [(5, 6)])
> 
> The correct approach is
> 
> | >>> a += (5, 6),
> | >>> a
> | ((1, 2), (3, 4), (5, 6))
> 
> The problem here is an ambiguity in the Python grammar where “(5, 6)” is 
> _not_ parsed as a double, but as a list of singles.  The ambiguity is 
> resolved by adding a trailing comma.  

There is no ambiguity in "(5, 6)". It is a tuple of two ints.  To make
a sequence of tuples (albeit a one-element sequence), you add a comma
to make it a one-element tuple, which is the same as "((5,6),)".

> (This is basic Python knowledge.)

Considering the gaps in your own Python knowledge, please try not
to be condescending when answering questions here.

For a discussion of mutability and immutability in Python, which will
help with the other part of the discussion, you might like:

    http://nedbatchelder.com/text/names1.html

--Ned.