How to Add Element If a Key Does Not Exist in Python Dictionary

Here are three ways to add an element if a key does not exist in Python dictionary:

  1. Using setdefault()
  2. Using if statement
  3. Using get()

Method 1: Using setdefault()

The dict.setdefault() method checks if a key exists in the dictionary, and if not, it adds the key with a specified default value.

If the key does exist, it leaves the dictionary unchanged.

Visual Representation

Using setdefault()

Example

# dictionary
icc_dict = {'IND': 1, 'AUS': 2}

# Add a new element if the key does not exist
icc_dict.setdefault('NZ', 4)

print(icc_dict)

# If the key already exists, the dictionary remains unchanged
icc_dict.setdefault('AUS', 5)

print(icc_dict)

Output

{'IND': 1, 'AUS': 2, 'NZ': 4}
{'IND': 1, 'AUS': 2, 'NZ': 4}

If no default value is passed, None is added as the default value.

Visual Representation

Add None as a default value

Example

icc_dict.setdefault('SA')
print(icc_dict)

Output

{'IND': 1, 'AUS': 2, 'NZ': 4, 'SA': None}

Method 2: Using if statement

The if statement checks whether a key exists in the dictionary and, if not, adds the key-value pair to the dictionary.

Visual Representation

Using if statement with in operator

Example

# dictionary
icc_dict = {'IND': 1, 'AUS': 2}

if 'NZ' not in icc_dict: 
 icc_dict['NZ'] = 4

print(icc_dict)

Output

{'IND': 1, 'AUS': 2, 'NZ': 4}

Method 3: Using get()

You can use dict.get() in combination with an assignment to add a key-value pair if the key does not exist.

This method is less efficient than the two previously mentioned methods, but still a valid approach and can be useful in certain contexts.

Example

# dictionary
icc_dict = {'IND': 1, 'AUS': 2}

# Use dict.get() to check the key and add it if it doesn't exist
if icc_dict.get('NZ') is None:
 icc_dict['NZ'] = 4

print(icc_dict)

Output

{'IND': 1, 'AUS': 2, 'NZ': 4}

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