Python check the whole loop before going to the else statement

Question

How do I run through the whole loop and then after go to else statement, if the if condition is false?

The output is:

No

No

Yes

But I only want it to jump to the else statement if all of the values does not equal!

test_1 = (255, 200, 100)
test_2 = (200, 200, 100)
test_3 = (500, 50, 200)

dict = {"test_1":test_1,
        "test_2":test_2,
        "test_3":test_3}


for item in dict:
   if dict[item] == (500, 50, 200):
        print('Yes')
   else:
        print('No')

So basicly the output should say, because one of the values was true.

Yes

FWIW, your question seems to have changed from 'How can I check if a dictionary contains a value?' to 'How can I extract the key associated with a value in a dict, if one exists?'. If that's correct, see http://stackoverflow.com/questions/8023306/get-key-by-value-in-dictionary — zehnpaard, Jan 11 '15 at 13:08

thefourtheye · Accepted Answer · 2015-01-11T14:27:43.803

7

You need to run the loop until you find a matche. You can use any function for this purpose, like this

if any(dict_object[key] == (500, 50, 200) for key in dict_object):
    print('Yes')
else:
    print('No')

We pass a generator expression to any function. The generator expression takes each and every item from the dict and checks if it is equal to (500, 50, 200). The moment it finds a match, the any will return True immediately and the rest of the iterations will not even take place. If none of the items match (500, 50, 200), any will return False and the No will be printed.

Edit: After a lengthy discussion with the OP in the chat, he actually wanted to know the item which matches as well. So, the better solution would be to go with for..else like in the other answer by NPE, like this

for key in dict_object:
   if key.startswith('test_') and dict_object[key] == (500, 50, 200):
        # Make use of `dict_object[key]` and `key` here
        break
else:
    print('No matches')

edited Jan 11 '15 at 14:27

answered Jan 11 '15 at 12:43

thefourtheye

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clean and simple, a great answer! :) – ladislas Jan 11 '15 at 12:48
Using this method, how would I print(item), since it's not referenced apparently? – Frederik Jan 11 '15 at 13:02
@Frederik You know the item you are searching for. So if there is a match, you can simply print it, right? – thefourtheye Jan 11 '15 at 13:02
`item` is a really bad name (from OP's original) for what is actually the `key` – zehnpaard Jan 11 '15 at 13:04
@thefourtheye Not actually, if I had test_3_id:2 in the dict :/ – Frederik Jan 11 '15 at 13:05
@Frederik I am sorry, I didn't understand that. Can you please explain? – thefourtheye Jan 11 '15 at 13:06
`if any(dict[item] == (500, 50, 200) for item in dict): print(dict[item]['id'])` I didn't show it, in the post, because I didn't know it would be a problem. @thefourtheye – Frederik Jan 11 '15 at 13:07
@Frederik Your dicts have just tuples as values. Can you please show the actual structure and what exactly you are trying to do? If that is entirely changes the meaning, then you may have to create another question :( – thefourtheye Jan 11 '15 at 13:10
Not if I don't know it's `(500,50,200)`. What if `(500,50,200)` it's a input from the user? – Frederik Jan 11 '15 at 13:11
@Frederik That will be stored in a variable I suppose? – thefourtheye Jan 11 '15 at 13:14
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/68588/discussion-between-frederik-and-thefourtheye). – Frederik Jan 11 '15 at 13:14

score 4 · Answer 2 · edited May 23 '17 at 12:15

But I only want it to jump to the else statement if all of the values does not equal!

Python's for-else construct can be used to do exactly that:

for item in dict:
   if dict[item] == (500, 50, 200):
        print('Yes')
        break
else:
    print('No')

For further discussion, see Why does python use 'else' after for and while loops?

However, in this particular instance I would not use an explicit loop at all:

print ("Yes" if (500, 50, 200) in dict.values() else "No")

score 1 · Answer 3 · edited Jan 11 '15 at 12:59

1

Maybe use in operator:

item_appears_in_dict = item in dict.values()
print "Yes" if item_appears_in_dict else "No"

edited Jan 11 '15 at 12:59

Sven Marnach

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answered Jan 11 '15 at 12:46

shevski

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As it stands this throws a syntax error. the second `print` in the second line shouldn't be there, as the ternary operator allows expressions but not statements. – zehnpaard Jan 11 '15 at 12:57

Python check the whole loop before going to the else statement

3 Answers3

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