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Dictionary Methods in Python | Set 2 (update(), has_key(), fromkeys()…)

  • Difficulty Level : Easy
  • Last Updated : 25 Jan, 2018

Some of the Dictionary methods are discussed in set 1 below

Dictionary Methods in Python | Set 1 (cmp(), len(), items()…)

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More methods are discussed in this article.



1. fromkeys(seq,value) :- This method is used to declare a new dictionary from the sequence mentioned in its arguments. This function can also initialize the declared dictionary with “value” argument.

2. update(dic) :- This function is used to update the dictionary to add other dictionary keys.




# Python code to demonstrate working of
# fromkeys() and update()
  
# Initializing dictionary 1
dic1 = { 'Name' : 'Nandini', 'Age' : 19 }
  
# Initializing dictionary 2
dic2 = { 'ID' : 2541997 }
  
# Initializing sequence
sequ = ('Name', 'Age', 'ID')
  
# using update to add dic2 values in dic 1
dic1.update(dic2)
  
# printing updated dictionary values
print ("The updated dictionary is : ")
print (str(dic1))
  
# using fromkeys() to transform sequence into dictionary
dict = dict.fromkeys(sequ,5)
  
# printing new dictionary values
print ("The new dictionary values are : ")
print (str(dict))

Output:

The updated dictionary is : 
{'Age': 19, 'Name': 'Nandini', 'ID': 2541997}
The new dictionary values are : 
{'Age': 5, 'Name': 5, 'ID': 5}

3. has_key() :- This function returns true if specified key is present in the dictionary, else returns false.

4. get(key, def_val) :- This function return the key value associated with the key mentioned in arguments. If key is not present, the default value is returned.




# Python code to demonstrate working of
# has_key() and get()
  
# Initializing dictionary
dict = { 'Name' : 'Nandini', 'Age' : 19 }
  
# using has_key() to check if dic1 has a key
if dict.has_key('Name'):
       print ("Name is a key")
else : print ("Name is not a key")
  
# using get() to print a key value
print ("The value associated with ID is : ")
print (dict.get('ID', "Not Present"))
  
# printing dictionary values
print ("The dictionary values are : ")
print (str(dict))

Output:

Name is a key
The value associated with ID is : 
Not Present
The dictionary values are : 
{'Name': 'Nandini', 'Age': 19}

5. setdefault(key, def_value) :- This function also searches for a key and displays its value like get() but, it creates new key with def_value if key is not present.




# Python code to demonstrate working of
# setdefault()
  
# Initializing dictionary
dict = { 'Name' : 'Nandini', 'Age' : 19 }
  
# using setdefault() to print a key value
print ("The value associated with Age is : ",end="")
print (dict.setdefault('ID', "No ID"))
  
# printing dictionary values
print ("The dictionary values are : ")
print (str(dict))

Output:

The value associated with Age is : No ID
The dictionary values are : 
{'Name': 'Nandini', 'Age': 19, 'ID': 'No ID'}

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