I have the following dictionary in python:
d = {'1': 'one', '3': 'three', '2': 'two', '5': 'five', '4': 'four'} I need a way to find if a value such as "one" or "two" exists in this dictionary.
For example, if I wanted to know if the index "1" existed I would simply have to type:
"1" in d And then python would tell me if that is true or false, however I need to do that same exact thing except to find if a value exists.
>>> d = {'1': 'one', '3': 'three', '2': 'two', '5': 'five', '4': 'four'} >>> 'one' in d.values() True Out of curiosity, some comparative timing:
>>> T(lambda : 'one' in d.itervalues()).repeat() [0.28107285499572754, 0.29107213020324707, 0.27941107749938965] >>> T(lambda : 'one' in d.values()).repeat() [0.38303399085998535, 0.37257885932922363, 0.37096405029296875] >>> T(lambda : 'one' in d.viewvalues()).repeat() [0.32004380226135254, 0.31716084480285645, 0.3171098232269287] >>> T(lambda : 'four' in d.itervalues()).repeat() [0.41178202629089355, 0.3959040641784668, 0.3970959186553955] >>> T(lambda : 'four' in d.values()).repeat() [0.4631338119506836, 0.43541407585144043, 0.4359898567199707] >>> T(lambda : 'four' in d.viewvalues()).repeat() [0.43414998054504395, 0.4213531017303467, 0.41684913635253906] The reason is that each of the above returns a different type of object, which may or may not be well suited for lookup operations:
>>> type(d.viewvalues()) <type 'dict_values'> >>> type(d.values()) <type 'list'> >>> type(d.itervalues()) <type 'dictionary-valueiterator'> 
d, the timings are effectively meaningless. In Python 3, dict.values() is a dictionary view, by default, and dict.itervalues() and dict.viewvalues() are gone. You could re-test this (with a larger dictionary) and use list(d.values()) to get the Python 2 behaviour, and iter(d.values()) to get the dict.itervalues() behaviour, but because both those versions require a global lookup and call, they'll absolutely be slower. Both do extra work that's not needed.In Python 3, you can use
"one" in d.values() to test if "one" is among the values of your dictionary.
In Python 2, it's more efficient to use
"one" in d.itervalues() instead.
Note that this triggers a linear scan through the values of the dictionary, short-circuiting as soon as it is found, so this is a lot less efficient than checking whether a key is present.
Python dictionary has get(key) function
>>> d.get(key) For Example,
>>> d = {'1': 'one', '3': 'three', '2': 'two', '5': 'five', '4': 'four'} >>> d.get('3') 'three' >>> d.get('10') None If your key does not exist, then it will return None value.
foo = d[key] # raise error if key doesn't exist foo = d.get(key) # return None if key doesn't exist Content relevant to versions less than 3.0 and greater than 5.0.
key:value and not key.
Use dictionary views:
if x in d.viewvalues(): dosomething() Different types to check the values exists
>>> d = {"key1":"value1", "key2":"value2"} >>> "value10" in d.values() False What if list of values
>>> test = {'key1': ['value4', 'value5', 'value6'], 'key2': ['value9'], 'key3': ['value6']} >>> "value4" in [x for v in test.values() for x in v] True What if list of values with string values
>>> test = {'key1': ['value4', 'value5', 'value6'], 'key2': ['value9'], 'key3': ['value6'], 'key5':'value10'} >>> values = test.values() >>> "value10" in [x for v in test.values() for x in v] or 'value10' in values True value in [... list comprehension over sequence ...], use any(value in sequence ...), to avoid creating a list object you don't use for anything else, and to short-circuit when the value has been found.You can use this:
d = {'1': 'one', '3': 'three', '2': 'two', '5': 'five', '4': 'four'} print("one" in d.values()) Or:
print(any([True for i,j in d1.items() if j == "one"])) In Python 3 you can use the values() function of the dictionary. It returns a view object of the values. This, in turn, can be passed to the iter function which returns an iterator object. The iterator can be checked using in, like this,
'one' in iter(d.values()) Or you can use the view object directly since it is similar to a list
'one' in d.values() 
iter() on a dictionary view; in will already use the object as an iterable (the type doesn't implement a dedicated __contains__ method). The only difference between 'one' in iter(d.values()) and 'one in d.values() is that you made Python do extra work (paying the cost of a global lookup for iter).