Check if a given key already exists in a dictionary in Python
Dictionary is an unordered collection of data in the form of key-value pairs separated by commas inside curly brackets. Dictionaries are indexed by keys. They are generally optimized to retrieve values when the key is known. Values (definitions) are mapped to a specific key (words) similar to that of a dictionary in the real world.
Now our task is to check if a given key exists in a dictionary or not. We can accomplish this through the ways below:
- Using the keys() method
- Using if and in
- Using has_key()
- Using keys() method:
This inbuilt method returns a list of all the available keys in a given dictionary. We use this along with the ‘in’ keyword.
Example:
def fun_check_key(dict, key): if key in dict.keys(): print("The key is present in dictionary", end ="\n") print("Corresponding value is:", dict[key]) else: print("The key is present in the dictionary") dict = {'One': '1', 'Two': '2', 'Three': 3} key = 'Two' fun check key(dict,key) key = 'Four' fun_check_key(dict, key)
Output:
- Using if and in:
Here we won’t necessarily use the keys() method. It just returns a boolean value, True if present else returns False
Example:
def fun_check_key(dict, key): if key in dict.keys(): print("The key is present in dictionary", end ="\n") print("Corresponding value is:", dict[key]) else: print("The key is present in the dictionary") dict = {'One': '1', 'Two': '2', 'Three': 3} key = 'Two' fun check key(dict,key) key = 'Four' fun_check_key(dict, key)
Output:
- Using has_key():
This method also returns a boolean value, True if the key is present in the dictionary else False. We use this method along with the if statement as shown below.
Example:
if dict.has_key(key):
Output:
This method is no longer supported by the versions Python 3 and above. We can only use it in Python 2. The output is much similar to the above mentioned ways.