Python dictionary values check not empty and not None

Question

I have a dictionary which may or may not have one or both keys 'foo' and 'bar'. Depending on whether both or either are available, I need to do different things. Here is what I am doing (and it works):

foo = None bar = None if 'foo' in data: if data['foo']: foo = data['foo'] if 'bar' in data: if data['bar']: bar = data['bar'] if foo is not None and bar is not None: dofoobar() elif foo is not None: dofoo() elif bar is not None: dobar()

This seems too verbose - what is the idiomatic way to do this in Python (2.7.10)?

@EricDuminil No, dofoobar() is different from dofoo() followed by dobar() — Anand
– Anand, Commented Sep 19, 2017 at 17:04
Wait, is it a typo with bar and email or do you really check two different keys? — Eric Duminil
– Eric Duminil, Commented Sep 19, 2017 at 17:11

Chris · Accepted Answer · 2017-09-19 19:58:02Z

6

You can use dict.get() to shorten your code. Rather than raising a KeyError when a key is not present, None is returned:

foo = data.get('foo') bar = data.get('email') if foo is not None and bar is not None: dofoobar() elif foo is not None: dofoo() elif bar is not None: dobar()

edited Sep 19, 2017 at 19:58

answered Sep 19, 2017 at 16:47

Chris

23.2k8 gold badges63 silver badges91 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Lukas Graf Over a year ago

An idiomatic alternative for the first if clause could be all([foo, bar]) if all that matters is truthyness, not exact comparison with None

Chris Over a year ago

@LukasGraf Well, I'm not exactly sure about that :| Wouldn't just doing if foo and bar be faster and cleaner if all that matters is truthyness?

yinnonsanders Over a year ago

@LukasGraf I'm not sure this was the intention, but in the OP's code all that matters is truthiness, because if data['foo'] doesn't evaluate to true, foo will never get a value other than None.

Lukas Graf Over a year ago

@ChristianDean that's true, that should be functionally equivalent and even cleaner. I don't think it would be significantly fast, as all() also short-circuits (returns on the first non-True element).

Lukas Graf Over a year ago

@yinnonsanders yeah, I noticed that as well. However, Christian's answer does demonstrate nicely that if you want to make that distinction, you compare the values to None (and do so using is instead of ==), which is why I like it.

|

Eric Duminil · Accepted Answer · 2017-09-19 17:21:58Z

Here's another way to refactor your code :

foo = data.get('foo') bar = data.get('bar') if foo: if bar: dofoobar() else: dofoo() elif bar: dobar()

I'm not sure it's cleaner or more readable than ChristianDean's answer, though.

Just for fun, you could also use a dict with boolean tuples as keys and functions as values:

{(True, True):dofoobar, (False, True):dobar, (True, False):dofoo}

You'd use it this way:

data = {'foo': 'something'} foo = data.get('foo') bar = data.get('bar') def dofoobar(): print('foobar!') def dobar(): print('bar!') def dofoo(): print('foo!') actions = {(True, True):dofoobar, (False, True):dobar, (True, False):dofoo} action = actions.get((foo is not None, bar is not None)) if action: action() #foo!

I like the first approach better than other answers (though the second one is more fun :-)) - actually, (in @ChristianDean's answer) I think checking for not None after data.get() does not validate that the strings are non-empty.

Wyrmwood · Accepted Answer · 2017-09-19 16:47:20Z

>>> data = {'foo': 1} >>> foo = data.get('foo') >>> foo 1 >>> bar = data.get('bar') >>> bar >>> bar is None True

Nimish Bansal · Accepted Answer · 2017-09-19 16:50:21Z

-1

foo = None bar = None try: foo=data["foo"] except: pass try: bar=data["bar"] except: pass if foo and bar: dofoobar() elif foo: dofoo() elif bar: dobar()

You can use try/except.Also get attribute is also perfect

answered Sep 19, 2017 at 16:50

Nimish Bansal

1,7594 gold badges24 silver badges42 bronze badges

2 Comments

Chris Over a year ago

You are right. EAFP is the commonly preferred idiom in Python. However, dict.get already implements the logic for you, so using it here just makes the code more verbose.

Nimish Bansal Over a year ago

ya I thought providing an alternative would also be fine

Collectives™ on Stack Overflow

Python dictionary values check not empty and not None

4 Answers 4

6 Comments

1 Comment

Comments

2 Comments

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

6 Comments

1 Comment

Comments

2 Comments

Related