Let's say I have an associative array like so: {'key1': 22, 'key2': 42}.
How can I check if key1 exists in the dictionary?
3 Answers
if key in array: # do something Associative arrays are called dictionaries in Python and you can learn more about them in the stdtypes documentation.
13 Comments
JAL
And, be sure to put the key name in quotes if it's a string.
Spencer Wood
@astroanu
if key not in array
Ray Salemi
Where did the word "array" come from in this answer?
cstrutton
As accepted answers go, this one is horrible. It in no way answers the question and is nothing more than a condescending link to the documentation. It is sad that Google ranks this so highly.
Rafal R
@cstrutton Please suggest improvements. At the moment of writing this answer I didn't feel more details is necessary.
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If you want to retrieve the key's value if it exists, you can also use
try: value = a[key] except KeyError: # Key is not present pass If you want to retrieve a default value when the key does not exist, use value = a.get(key, default_value). If you want to set the default value at the same time in case the key does not exist, use value = a.setdefault(key, default_value).
3 Comments
aaronasterling
It should be noted that you should only use the
try/except case if you expect that the key will be present approaching 100% of the time. otherwise, if in is prettier and more efficient. +1 for mentioning the other possibilities.
Yannic Hamann
Interesting, I remember that I read somewhere in the official docs that it is better to ask for forgiveness than permission...
Avo Asatryan
from point of view of performance , try/expect is better if you are dealing with dict with many keys
Another method is has_key() (if still using Python 2.X):
>>> a={"1":"one","2":"two"} >>> a.has_key("1") True 
8 Comments
aaronasterling
has_key is deprecated, removed in python 3, and half as fast in python 2aaronasterling
yes it is deprecated in 2.x and yes it is half as fast in python 2.x.
aaronasterling
deprecated applies to all new code. once it's deprecated, don't use it anymore.
Tim W.
the form 'key in dict' has existed since 2.2
ghostdog74
we could go on and on about this, the fact remains, its still an alternative option for <=2.5.
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'key1' in {'key1': 22, 'key2': 42}.keys()refer to thekeys()method in Dictionary