Python void/null function

Question

Python noob so I might be going about this the wrong way

I want to use a try/except block to find if a value in a dict isn't set like

try:
    if entry['VALUE1'] == None: void()
    if entry['VALUE2'] == None: void()
except KeyError:
    print "Values not Found"

Of course the 'void' function doesn't exist, is there anything I can do to get round this so that code will work properly

It's not clear from this question, but maybe what you're looking for is a defaultdict? Whenever you access an entry that doesn't exist, it's automatically added with a default value, so you don't have to worry when doing things like entry['VALUE1'] += value. — Adam Rosenfield
– Adam Rosenfield, Commented Jun 13, 2011 at 3:50
Just as a side note, its nicer to do if entry['VALUE1'] is None: — Jakob Bowyer
– Jakob Bowyer, Commented Jun 13, 2011 at 8:21

Rafe Kettler · Accepted Answer · 2011-06-13 03:38:49Z

8

Try replacing void() with pass.

Of course, in practice, you can just do if key in some_dict:. But if you ever need a "do nothing" in a block, pass is what you're looking for.

answered Jun 13, 2011 at 3:38

Rafe Kettler

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Comments

Zeke · Accepted Answer · 2011-06-13 03:50:32Z

3

Try:

if "VALUE1" in entry:
    foo()

to determine if the "VALUE1" string is in the set of keys of the entry dict.

Your logic would probably look something like:

if "VALUE1" not in entry or "VALUE2" not in entry:
    print "Values not found"

The try block is completely unnecessary for this test.

edited Jun 13, 2011 at 3:50

answered Jun 13, 2011 at 3:38

Zeke

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Comments

jcomeau_ictx · Accepted Answer · 2011-06-13 03:38:27Z

0

if entry.has_key('VALUE1'):
 do_something()

or

if 'VALUE1' in entry:
 do_something()

answered Jun 13, 2011 at 3:38

jcomeau_ictx

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Comments

Bobby Powers · Accepted Answer · 2011-06-13 03:57:38Z

0

I would suggest making a function to help you out:

contains_all_keys = lambda d, keys: reduce(lambda a, b: a and b, map(lambda k: k in d, keys))
di = {'a':'some val', 'b':'some other val'}
if contains_all_keys(di, ['a', 'b']):
    print 'a and b present'
if not contains_all_keys(di, ['a', 'b', 'c']):
    print 'missing keys'

answered Jun 13, 2011 at 3:57

Bobby Powers

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2 Comments

DSM Over a year ago

I think both "all(key in di for key in ['a','b'])" and "set(['a','b']).issubset(di)" are clearer than a nested triple lambda with a map and a reduce.

Bobby Powers Over a year ago

hah I think you're absolutely right. I didn't know about all(), thats quite nice with list comprehensions.

SingleNegationElimination · Accepted Answer · 2011-06-13 04:27:25Z

0

If you just want to evoke the exception, through a key lookup, the if is not neccesary. It's sufficient to just express the lookup on a line by itself, such as:

>>> a = {}
>>> a['value']
Traceback (most recent call last):
  File "<ipython console>", line 1, in <module>
KeyError: 'value'
>>>

answered Jun 13, 2011 at 4:27

SingleNegationElimination

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