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python dictionary share|improve this question edited Jul 15 '15 at 23:50 Eric Leschinski 49.2k25222195 asked Apr 12 '12 at 2:11 lonehangman 4601513 4 Key error generally means the key doesn't more stack exchange communities company blog Stack Exchange Inbox Reputation and Badges sign up log in tour help Tour Start here for a quick overview of the site Help Center Detailed Browse other questions tagged python dictionary or ask your own question. Now instead of using 'Dict['a'], we use the NEARLY synonymous 'get' method. >>> Dict.get('a',0) 0 No error. http://edsdefence.com/python-key/key-error-4-python.php

asked 2 years ago viewed 10138 times active 2 years ago Blog How Do Software Developers in New York, San Francisco, London and Bangalore… Related 24Why aren't there explicit access modifiers asked 4 years ago viewed 162843 times active 9 months ago Blog How Do Software Developers in New York, San Francisco, London and Bangalore… Linked 0 strange error in loops 2 We could write an if statement, using the result of this method to determine whether or not we should try to access the given key. Why are Matthew, Mark, and Luke called 'synoptic' gospels? https://wiki.python.org/moin/KeyError

Python Keyerror Exception

Then the get method would be defined. I would like to be able to print the exception that was thrown. But how do we put this into use? Forever more hot questions question feed lang-py about us tour help blog chat data legal privacy policy work here advertising info mobile contact us feedback Technology Life / Arts Culture /

So 0 is returned in this case. Just to be clear in the following discussion, let's empty the dictionary: wordtag={} This statement declares wordtag as an empty dictionary (a hash table or alist in other languages). The following is more readable and gets the same thing done: >>> wordtag['walk']= wordtag.get('walk',{}) >>> wordtag['walk'].get('VBZ',0) 0 The first line is an assignment statement which sets wordtag['walk'] to the empty dictionary, Python Keyerror Get Key For example, checking if a file exists and then trying to read from it - at least 3 things I can think of off the top of my head can go

def keyCheck(key, arr, default): if key in arr.keys(): return arr[key] else: return default myarray = {'key1':1, 'key2':2} print keyCheck('key1', myarray, '#default') print keyCheck('key2', myarray, '#default') print keyCheck('key3', myarray, '#default') Output: 1 Python Keyerror 0 If it is part of the engine i am afraid nothing can't be done. –RanRag Apr 12 '12 at 5:24 It's part of my code –lonehangman Apr 15 '12 share|improve this answer answered Jan 23 '14 at 21:14 Eugene 573310 3 "From a pragmatic point of view, throwing/catching is much slower then checking if the key is in table" And for incrementing values this gives the somewhat readable: >>> wordtag['walk']= wordtag.get('walk',{}) >>> wordtag['walk']['VBZ'] = wordtag['walk'].get('VBZ',0) +1 End of discussion.

But there is a more fundamental difference. Python Raise Keyerror try: connection = manager.connect("I2Cx") except KeyError, e: print 'I got a KeyError - reason "%s"' % str(e) except: print 'I got another exception, but I should re-raise' raise ...because you probably Why is this child portrait not compelling? Gracefully handle Solr search connectivity issues How should a "working mathematician" think about sets? (ZFC, category theory, urelements) more hot questions question feed lang-py about us tour help blog chat data

Python Keyerror 0

You can't guarantee the caller isn't going to change its implementation later on down the line, so you should do the thing with the least side-effects. over here You're able to do something like: try: foo += bar except TypeError: pass else: return some_more_work(foo) Isn't that going to lead to swallowing all kinds of weird errors that are probably Python Keyerror Exception share|improve this answer edited Apr 22 '13 at 18:36 answered Apr 22 '13 at 18:25 RichieHindle 149k34257337 add a comment| up vote 1 down vote You can also try to use Python Key Error But Key Exists asked 3 years ago viewed 31183 times active 19 days ago Blog How Do Software Developers in New York, San Francisco, London and Bangalore… Related 65Using python “with” statement with try-except

To define the value we have to explicitly assign what 'get' returns. >>> Dict['a']=Dict.get('a',0) >>> Dict['a'] 0 Python provides a single function called setdefault that performs both retrieval and setting. weblink Movie about a man who becomes a genius because of a brain tumor? What do we do?   P Y T H O N   Get: The solution The python dictionary 'method 'get' is set up to do just what we want. First As long as your keys are of the allowed types specified above, you can mix and match dictionary key types in any which way you like. Keyerror Python Json

For example: >>> mydict = {'a':'1','b':'2'} >>> mydict['a'] '1' >>> mydict['c'] Traceback (most recent call last): File "", line 1, in KeyError: 'c' >>> So, try to print the content But we never get to step (b) because step (a) raises a Key Error. try: connection = manager.connect("I2Cx") except KeyError, e: print 'I got a KeyError - reason "%s"' % str(e) except IndexError, e: print 'I got an IndexError - reason "%s"' % str(e) There navigate here So when we assign the string 'APIKEY' to varible key ,it doesn't actually work .And what happened when we run these code and get a correct return in Codecademy ?

x = d['2'] ... Os Error In Python None) or you do if data: do_work(data). stringKeyDictionary = { 'Anna' : 1481.10 }
Fig. 1: A dictionary containing a str based key Here, the number 25 is the key represented as an integer, and the

If you omit default_value, None is returned if the key is missing.

Hot Network Questions A world with a special political system James Potter and the Cloak of Invisibility - Why didn't he use it to hide the family from Voldemort? Keys can technically be made up of any hashable type, but for now let's just consider keys made of strings, numbers, tuples, or any combination thereof. So we have to do this: >>> wordtag['walk']={} Assign an empty dictionary as the value of 'walk' in wordtag. Keyerror Django KeyError: 'walk' Of course we get an error.

If I try the same thing with a divide by zero operation it is caught and reported properly in both cases. From the official python docs: exception KeyError Raised when a mapping (dictionary) key is not found in the set of existing keys. As an example, consider the following (incomplete) dictionary of orchestral instruments: >>> instDictionary = {'Winds': ['Clarinet', 'Flute', 'Oboe']}
>>> instDictionary['Brass'] = ['Trombone', 'Trumpet', 'Tuba']
>>> instDictionary['Strings'] = his comment is here QiitaItemsPythonpythonのdictionaryでKeyErrorを出さないようにするPython8252dictionary12辞書型123Like0Comment sue71 posted at 2015-01-04StockStock Report article More than 1 year has passed since last update.

A dictionary is an unordered set of key-value pairs. So >>> D.setdefault('a',0) 0 is equivalent to: >>> Dict['a']=Dict.get('a',0) Both Dict.get('a',0) zand Dict.setdefault('a',0) differ from Dict['a'] in their exception-raising behavior. But the deciding factor is this: You are basically building a V x T matrix, where V is vocabulary size and T is number of tags. Python has very good error/exception handling.

This forum is now read-only. Additionally, there is the possibility in some situations where that dict could be modified in between the test and the access. –whatsisname Jan 24 '14 at 0:17 @whatsisname - Like get it takes a default which is the value returned if the given key has no value; unlike get, setdefault also sets the dictionary key to that value. If you don't want to have an exception but would rather a default value used instead, you can use the get() method: 1 default = 'Scruffy' 2 a = adict.get('dogname', default)