[Tutor] setdefault method

[Carroll, Barry]

Greetings:

What is the purpose of the dictionary method setdefault(k[, x])?

For example assume the following dictionary:

>>> colors = {'green':(0,255,0), 'red':(255,0,0), 'blue':(0,0,255), 'white':(255,255,255), 'black':(0,0,0)}
>>>

Now, execute the statement:

>>> colors.setdefault('black')
(0, 0, 0)
>>>

I would expect that future references to colors, with no argument or a null argument, would return the value of colors['black'], e.g.:

>>> colors[]
(0, 0, 0)
>>> colors
(0, 0, 0)
>>>

or some similar syntax.  This is not the case, however. The actual behavior is:

>>> colors
{'blue': (0, 0, 255), 'black': (0, 0, 0), 'white': (255, 255, 255), 'green': (0, 255, 0), 'red': (255, 0, 0)}
>>> colors[]
  File "<input>", line 1
    colors[]
           ^
SyntaxError: invalid syntax
>>>

So, what then is the proper use of setdefault()?  And, if d.setdefault does not actually assign a default value for d, is there a way to do this?

As always, thanks in advance for your responses.  
 
Barry
barry.carroll at psc.com
541-302-1107
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