[Tutor] Appending to many lists with list comprehension

[jfouhy@paradise.net.nz]

Quoting Bernard Lebel <3dbernard at gmail.com>:

> aList = [ [], [] ]
> 
> 
> # Iterate attributes of the top object		
> for oAttribute in oObj.attributes:
> 	
> 	# Append to list 0 the attribute "type" of the current attribute
> 	aList[0].append( str(oAttribute.type) )
> 
> 	# Append to list 1 the attribute "name" of the current attribute
> 	aList[1].append( str(oAttribute.name) )
> 
> Instead of having two separate lists and a for loop, I'd like to perform
> a list comprehension that would do this all in one go, if this is
> doable.

You could do:

[(str(x.type), str(x.name)) for x in oObj.attributes]

This won't produce the same result as your code; it will give you a list of
pairs, rather than a pair of lists.

For a list of pairs, you could do it in two list comprehensions:

[[str(x.type) for x in oObj.attributes], [str(x.name) for x in oObj.attributes]]

Or you could do a bit of subtle magic with zip:

zip(*[(str(x.type), str(x.name)) for x in oObj.attributes])

Or maybe some bonus magic:

[[str(x.__dict__[y]) for y in dir(x) if not y.startswith('_')] for x in
oObj.attributes]

This will give you a list of lists, analogous to the list of tuples earlier.  It
will grab all the attributes not starting with an _ (so it should avoid the
baggage all objects come with, but caution is still advised).

[is using __dict__ here the best way of doing this?]

Of course, you can unzip it as before:

zip(*[[str(x.__dict__[y]) for y in dir(x) if not y.startswith('_')] for x in
oObj.attributes])

HTH!

-- 
John.