Question

I decision trees implemented in Python as dictionaries. Example:

sampletree = {'spl':'foo', 'go_r':{'cut':150} ,  'l':{'val':100}, 'r':{'val':200}}

I have a recursive function prints the tree:

def TREE_PRINT(tree, indent=''):
    #is this a leaf node?
    if 'val' in tree:
        print str(tree['val'])
    else:
        #print the criteria
        print 'split: '+ str(tree['spl']) + ' ' + str(tree['go_r'])
        #print the branches
        print indent+'L->', TREE_PRINT(tree['l'], indent+'  ')
        print indent+'R->', TREE_PRINT(tree['r'], indent+'  ')

How do I suppress the None’s that are printed when I run the function?

TREE_PRINT(sampletree)
split: foo {'cut': 150}
L-> 100
None
R-> 200
None

I tried returning ”, but then I get line unwanted extra line breaks.
I’m building off of the ‘printtree’ function from page 151 in Programming Collective Intelligence.

Answer 1

The return value of your function is None. Don’t print the return value of your function – just call your function.

def TREE_PRINT(tree, indent=''):
    #is this a leaf node?
    if 'val' in tree:
        print str(tree['val'])
    else:
        #print the criteria
        print 'split: '+ str(tree['spl']) + ' ' + str(tree['go_r'])
        #print the branches
        print indent+'L->',
        TREE_PRINT(tree['l'], indent+'  ')

        print indent+'R->',
        TREE_PRINT(tree['r'], indent+'  ')

Result

split: foo {'cut': 150}
L-> 100
R-> 200

See it working online: ideone