Python: how can I check if the key of an dictionary exists ?

Question

Possible Duplicate:
What is a good way to test if a Key exists in Python Dictionary

Let's say I have an associative array like so: {'key1': 22, 'key2': 42}.

How can I check if key1 exists in the dictionary?

Answer 1

if key in array:
  # do something

Associative arrays are called in Python dictionaries and you can learn more about them here:
http://docs.python.org/library/stdtypes.html#dict

Answer 2

another method is has_key() (if still using 2.X)

>>> a={"1":"one","2":"two"}
>>> a.has_key("1")
True

Answer 3

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).