Usage and examples of Python dictionary setdefault()

Python dictionary methods

The setdefault() method returns the value of the specified key. If the key does not exist, it inserts a key with the specified value.

The syntax of setdefault() is:

dict.setdefault(key[,　default_value])

setdefault() parameters

setdefault() accepts up to two parameters:

• key -The key to be searched in the dictionary

• default_value(Optional)- If the key is not in the dictionary, insert the value of the key with the value default_value into the dictionary.
  If not provided, default_value will be None.

setdefault() returns

setdefault() returns:

• The value of the key (if it is in the dictionary)

• None - If the key is not in the dictionary and default_value is not specified, it will be None

• default_value - If the key is not in the dictionary and default_value is specified

Example1：How does setdefault() work when the key is in the dictionary?

person　=　{'name':　'Phill',　'age':　22}
age　=　person.setdefault('age')
print('person　=　',person)
print('Age　=　',age)

When running this program, the output is:

person　=　　{'name':　'Phill',　'age':　22}
Age　=　　22

Example2：How does setdefault() work when the key is not in the dictionary?

person　=　{'name':　'Phill'}
#　key is not in the dictionary
salary　=　person.setdefault('salary')
print('person　=　',person)
print('salary　=　',salary)
#　key is not in the dictionary
#　provided default_value
age　=　person.setdefault('age',　22)
print('person　=　',person)
print('age　=　',age)

When running this program, the output is:

person　=　　{'name':　'Phill',　'salary':　None}
salary　=　　None
person　=　　{'name':　'Phill',　'age':　22,　'salary':　None}
age　=　　22

Python dictionary methods