How can I check if a key exists in a 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?

if key in array:
  # do something

Associative arrays are called dictionaries in Python and you can learn more about them in the stdtypes documentation.

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).

Another method is has_key() (if still using Python 2.X):

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