Python 如何检查字典中是否存在键？
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How can I check if a key exists in a dictionary?
提问by aneuryzm
Let's say I have an associative array like so: {'key1': 22, 'key2': 42}.
比方说，我有一个关联数组，像这样：{'key1': 22, 'key2': 42}。
How can I check if key1exists in the dictionary?
如何检查key1字典中是否存在？
采纳答案by Rafa? Rawicki
if key in array:
# do something
Associative arrays are called dictionaries in Python and you can learn more about them in the stdtypes documentation.
关联数组在 Python 中称为字典，您可以在stdtypes 文档中了解有关它们的更多信息。
回答by ghostdog74
Another method is has_key()(if still using Python 2.X):
另一种方法是has_key()（如果仍在使用 Python 2.X）：
>>> a={"1":"one","2":"two"}
>>> a.has_key("1")
True
回答by Marc
If you want to retrieve the key's value if it exists, you can also use
如果要检索键的值（如果存在），也可以使用
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).
如果要在键不存在时检索默认值，请使用
value = a.get(key, default_value). 如果您想同时设置默认值以防键不存在，请使用
value = a.setdefault(key, default_value).
