[Tutor] print as columns

[Mike Serpa]

> 
> I have a couple suggestions regarding your printListColumns:
> 
> 1) you can find the longest in a list of lists by using the
> reduce function which keeps applying the function to 
> successive pairs of elements from a list:
> 
> n=len(reduce(lambda a,b:max(a,b),l))
>   ---        ------------------- -
>    ^            ^                ^->the list of lists (called Lists
> in
> your program)
>    |            |
>    |            |_ the function which returns the longer of two lists
>    |
>    |_ when the reduce is done we will know the longest list, len
> gives the
> length of it
> 
> Example:
> 
> a=[1,2,3,4]
> b=[5,6,7]
> c=[8,9,10,11,12]
> 
> n=len( reduce( lambda a,b:max(a,b), [a,b,c] ))
> 
> n is 5


Couldn't we shorten this to:
n=len(max(lists))   

It seems that everything I figure out how to do is already in a module
somewhere.  Question for expert Python coders (or any lang.) Do you
ever  get to the stage where you don't have to constantly look things
up in the lang docs?




> 
> 2) Instead of padding, you might consider using the try/except 
> construction to not print the list elements that don't 
> exist.  Here's how it looks for a list of 3 elements which is to be
> printed in 5 rows.
> 
> 	for j in range(5):
> 		try:
> 			print str(l[j].ljust(20),  #if l[j] exists, print it
> 		except:
> 			print ''.ljust(20)  #otherwise format a null string
> 
> Thanks for the thought provoking post.
> 

So I don't have to lace them then.

So we get:

def printListColumns(*lists):
    longestLength=len(max(lists)) 
    for row in range(longestLength):  # number of rows
        for column in lists:          # number of columns
            try:
                print str(column[row]).ljust(20),    # print if exists
            except:
                print ''.ljust(20)                   # blank if not
        print 

Great!
We've gone from 20 lines to 15 to 9.  More importantly it's now much
simpler.

The only thing I can think to add is a max number of columns so it
doesn't go off the screen. Or if columns is > 4 then split into two
tables. Or adjust columns to largest element, etc. Don't need to yet
for what I'm using if for, but will be easier now. Thanks.

Mike







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