It is recommended to use the in keyword to check whether a key exists in the dictionary because it is concise, efficient and highly readable; 2. It is not recommended to use the get() method to determine whether the key exists, because it will be misjudged when the key exists but the value is None; 3. You can use the keys() method, but it is redundant, because in defaults to check the key; 4. When you need to get a value and the expected key usually exists, you can use try-except to catch the KeyError exception. The most recommended method is to use the in keyword, which is both safe and efficient, and is not affected by the value of None, and is suitable for most scenarios.
In Python, checking for a key in a dictionary is a very common operation. There are several simple and effective ways to achieve it. The following is an example to illustrate the most commonly used methods.

? Method 1: Use the in
keyword (recommended)
This is the most intuitive and commonly used method.
person = { 'name': 'Alice', 'age': 30 } if 'name' in person: print("key 'name' exists") else: print("key 'name' does not exist")
Output:

The key 'name' exists
? Advantages: Concise, efficient, and highly readable.
? Method 2: Use get()
method to judge
The get()
method can get the value corresponding to the key. If the key does not exist, it returns None
or the specified default value.

if person.get('age') is not None: print("key 'age' exists")
?? Note: This method has limitations - if the key exists but the value is None
, it will be misjudged as "not existed".
For example:
data = {'city': None} if data.get('city') is not None: print("exist") # else will not be executed: print("Misconsidered as non-existent") # will execute, but the key actually exists!
? Therefore, it is not recommended to use
get()
to determine whether the key exists unless you are sure that the value will not beNone
.
? Method 3: Use keys()
method
Although yes, it is not recommended because it is unnecessary.
if 'name' in person.keys(): print("Key exists")
? In fact,
in person
is checkingperson.keys()
by default, soperson.keys()
can be omitted.
? Method 4: Use try-except
to catch exceptions (suitable for scenarios where values are needed)
When you not only want to determine whether it exists, but also use its value, you can use try-except
.
try: value = person['name'] print(f" key exists, value is: {value}") except KeyError: print("Key does not exist")
? Suitable for scenarios where you "expect the keys to exist in most cases", such as configuration resolution.
Summary: Recommended practices
# Best practices if 'name' in person: print("Key exists")
- Simple, safe and efficient.
- No exception is thrown.
- Not affected by the value of
None
.
Basically, these commonly used methods are all. It is enough to in
in daily development, which is simple and not easy to make mistakes.
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