<\/span><\/h4>\n\n\n\nLet say we already have a dictionary with some elements in it.<\/p>\n\n\n\n
empDict = {1: 'Mark', 2: 'Bob'}<\/pre>\n\n\n\nUpdating existing discretionary value:<\/strong><\/p>\n\n\n\nIf the key is already present in the dictionary, it will overwrite the value, to preserve the uniqueness of the key.<\/p>\n\n\n\n
empDict = {1: 'Mark', 2: 'Bob'}\nempDict[2] = 'Alice'\n\nprint(empDict)\n\n# Output: {1: 'Mark', 2: 'Alice'}<\/pre><\/div>\n\n\n\nAdding a new element to the dictionary:<\/strong><\/p>\n\n\n\nIf the key is not present in the dictionary, it adds a new key-value pair in the dictionary.<\/p>\n\n\n\n
empDict = {1: 'Mark', 2: 'Bob'}\nempDict[3] ='Alice'\n\nprint(empDict)\n\n# Output: {1: 'Mark', 2: 'Bob', 3:'Alice'}<\/pre><\/div>\n\n\n\nNote: The syntax for adding and updating elements in the dictionary is the same.<\/p>\n\n\n\n
Adding a new element to the dictionary with the same key:<\/strong><\/p>\n\n\n\nWhat if we try to add a new element in the dictionary with the key which is already present in the dictionary?<\/p>\n\n\n\n
If you try to add the same element in the dictionary with the same keys, it overwrites the key value.<\/p>\n\n\n\n
It is similar to updating the value of the given key in the dictionary.<\/p>\n\n\n\n
<\/span>How to delete or remove elements from the dictionary?<\/span><\/h4>\n\n\n\nLet’s consider this dictionary.<\/p>\n\n\n\n
# create a dictionary\nsquaresDict = {1:1, 2:4, 3:9, 4:16, 5:25}<\/pre>\n\n\n\nHow to remove a particular element from the dictionary using pop?<\/strong><\/p>\n\n\n\nYou have to specify the key.<\/p>\n\n\n\n
Here is a way of doing this using the simple pop method.<\/p>\n\n\n\n
print(squaresDict .pop(4)) \n\n# Output: 16<\/pre>\n\n\n\nThe pop method returns the value of the dictionary element you are removing.<\/p>\n\n\n\n
When you print the dictionary after performing the pop operation, you don’t see that element in the dictionary.<\/p>\n\n\n\n
print(squaresDict ) \n\n# Output: {1: 1, 2: 4, 3: 9, 5: 25}<\/pre>\n\n\n\nHow to remove an arbitrary item for which you know key-value pair using pop?<\/strong><\/p>\n\n\n\nUse popitem<\/code> method for this. You need to provide both key and value here.<\/p>\n\n\n\nprint(squaresDict .popitem())\n# Output: (1, 1)\n\nprint(squaresDict)\n# Output: {2: 4, 3: 9, 5: 25}<\/pre>\n\n\n\nHow to remove an element from a dictionary using del?<\/strong><\/p>\n\n\n\nJust like the pop method you can also use the del<\/code> object.<\/p>\n\n\n\n# delete a particular item\ndel squaresDict [5]\n\nprint(squaresDict )\n# Output: {2: 4, 3: 9}<\/pre>\n\n\n\nThe keyword del is not only specific to the dictionary. It is a generic way of deleting any Python object.<\/p>\n\n\n\n
<\/span>Difference between del and pop method in the dictionary.<\/span><\/h4>\n\n\n\n- The del object simply delete the element from the dictionary.<\/li>
- In case of the pop method, along with deleting an element from a dictionary it also returns the value of the target element.<\/li><\/ul>\n\n\n\n
<\/span>How to delete all the items in the dictionary?<\/span><\/h4>\n\n\n\nNow we are not interested in deleting a single element. What if you want to delete the complete dictionary? Or want to clear all the elements in the dictionary?<\/p>\n\n\n\n
Dictionary has a special method called clear to\u00a0delete all the items from the dictionary.<\/p>\n\n\n\n
squaresDict = {1:1, 2:4, 3:9, 4:16, 5:25}\nsquaresDict .clear() # remove all items\n\nprint(squaresDict )\n\n# Output: {}<\/pre><\/div>\n\n\n\nYou can see the empty dictionary as an output.<\/p>\n\n\n\n
How to Delete Complete Dictionary?<\/strong><\/p>\n\n\n\nEarlier we have tried del object for deleting a particular item from the dictionary. Now you want to delete the complete dictionary object instead of just removing all elements from the dictionary.<\/p>\n\n\n\n
Using a del<\/code> object, you can delete the complete dictionary.<\/p>\n\n\n\nsquaresDict = {1:1, 2:4, 3:9, 4:16, 5:25}\ndel squaresDict # delete the dictionary itself<\/pre><\/div>\n\n\n\nAfter deleting the dictionary object, when you try to print the dictionary, it throws an error.<\/p>\n\n\n\n
Difference between del and clear method:<\/strong><\/p>\n\n\n\nIf you delete the dictionary using del, it wipes out the complete dictionary object.<\/p>\n\n\n\n
If you try to access the dictionary, it will through an error.<\/p>\n\n\n\n
empDict = {1: 'Mark', 2: 'Bob'}\ndel empDict\nprint(empDict)<\/pre><\/div>\n\n\n\nTraceback (most recent call last):\nFile \"\/home\/7d2f6393bbb812bde2a7f038b346bb7e.py\", line 5, in\nprint(empDict )\nNameError: name 'empDict' is not defined<\/strong><\/pre>\n\n\n\nIt means the dictionary has been deleted.<\/p>\n\n\n\n
Method clear()<\/code> does not delete the dictionary. It removes all the items from the dictionary. Dictionary will be empty.<\/p>\n\n\n\n<\/span>Dictionary Membership Test<\/span><\/h4>\n\n\n\nWhat is the membership test?<\/p>\n\n\n\n
Check if the key is present in the dictionary or not.<\/p>\n\n\n\n
squaresDict = {1: 1, 3: 9, 5: 25, 7: 49, 9: 81}<\/pre>\n\n\n\nYou can do the membership test using ‘in’.<\/p>\n\n\n\n
Syntax:<\/strong><\/p>\n\n\n\n<expected_key> in <dictionary_object><\/pre>\n\n\n\nIt returns true if the key is present in the dictionary.<\/p>\n\n\n\n
It returns false if the key is not present in the dictionary.<\/p>\n\n\n\n
Example:<\/strong><\/p>\n\n\n\nprint(1 in squaresDict)\n# Output: True\n\nprint(4 in squaresDict)\n# Output: False<\/pre>\n\n\n\n“not in”<\/strong><\/p>\n\n\n\nYou can also apply negation ‘not in’.<\/p>\n\n\n\n
Slightly different. If the key is not present in the dictionary, it returns True.<\/p>\n\n\n\n
Example:<\/strong><\/p>\n\n\n\nprint(2 not in squaresDict)\n# Output: True<\/pre>\n\n\n\n<\/span>Iterating Through Python Dictionary<\/span><\/h4>\n\n\n\nMany times you have to iterate over all the elements in the dictionary.<\/p>\n\n\n\n
It is simple.<\/p>\n\n\n\n
squares = {1: 1, 3: 9, 5: 25, 7: 49, 9: 81}\nfor i in squares:\n print(squares[i])<\/pre><\/div>\n\n\n\nThe above example will print all the dictionary elements one-by-one.<\/p>\n\n\n\n
Inside for loop, you can write a code to perform any operations on each element of the dictionary.<\/p>\n\n\n\n
You can also use the items method for iteration.<\/p>\n\n\n\n
Using items methods for iterating over the dictionary.<\/p>\n\n\n\n
squares = {1: 1, 3: 9, 5: 25, 7: 49, 9: 81} \nfor item in squares.items(): \n print(item)<\/pre><\/div>\n\n\n\n<\/span>How to convert Sequence to Dictionary?<\/span><\/h4>\n\n\n\nHow to create a dictionary from the sequence?<\/strong><\/p>\n\n\n\nYou can use each sequence as a key-value pair. Here is a simple code that works for you.<\/p>\n\n\n\n
empDict = dict([(1,'Mark'), (2,'Bob')])<\/pre>\n\n\n\nWe are using the same dict()<\/code> method that was used earlier for creating a dictionary object.<\/p>\n\n\n\n<\/span>Python Dictionary Methods<\/span><\/h3>\n\n\n\nLook at some of the methods you can use with the dictionary.<\/p>\n\n\n\n
- clear(): <\/strong>Remove all items from the dictionary.<\/li>
- copy(): <\/strong>Return a shallow copy of the dictionary.<\/li>
- fromkeys(seq[, v]): <\/strong>Return a new dictionary with keys from seq and value equal to v (defaults to None).<\/li>
- get(key[,d]): <\/strong>Return the value of key. If the key does not exist, return d (defaults to None).<\/li>
- items(): <\/strong>Return a new view of the dictionary’s items (key, value).<\/li>
- keys(): <\/strong>Return a new view of the dictionary’s keys.<\/li>
- pop(key[,d]): <\/strong>Remove the item with a key and return its value or return ‘d’ if the key is not found. If d is not provided and the key is not found, raises KeyError.<\/li>
- popitem(): <\/strong>Remove and return an arbitrary item (key, value). Raises KeyError if the dictionary is empty.<\/li>
- setdefault(key[,d]): <\/strong>If the key is in the dictionary, return its value. If not, insert key with a value of d and return d (defaults to None).<\/li>
- update([other]): <\/strong>Update the dictionary with the key\/value pairs from other, overwriting existing keys.<\/li>
- values(): <\/strong>Return a new view of the dictionary’s values<\/li><\/ol>\n\n\n\n
Let’s take some examples of dictionary methods.<\/p>\n\n\n\n
Write a Python code to initialize the dictionary with zero value for all specified keys.<\/strong><\/p>\n\n\n\nmarks = {}.fromkeys(['Math','English','Science'], 0)\nprint(marks)\n\n# Output: {'English': 0, 'Math': 0, 'Science': 0}<\/pre><\/div>\n\n\n\nUsing items methods for iterating over the dictionary.<\/strong><\/p>\n\n\n\nfor item in marks.items():\n print(item)<\/pre>\n\n\n\nUsing the keys method to get all the keys present in the dictionary.<\/strong><\/p>\n\n\n\nlist(sorted(marks.keys()))\n\n# Output: ['English', 'Math', 'Science']<\/pre>\n\n\n\n<\/span>Python Dictionary List Comprehension<\/span><\/h3>\n\n\n\nYou can use the comprehension technique to generate the dictionary items.<\/p>\n\n\n\n
Write a python code to store the square as the value for each key.<\/strong><\/p>\n\n\n\nsquares = {x: x*x for x in range(6)}\nprint(squares)\n\n# Output: {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}<\/pre><\/div>\n\n\n\nThis is simply equivalent to the following code.<\/p>\n\n\n\n
squares = {}\nfor x in range(6):\n squares[x] = x*x<\/pre><\/div>\n\n\n\nWe can add some more conditions to the comprehension technique.<\/p>\n\n\n\n
odd_squares = {x: x*x for x in range(11) if x%2 == 1}\nprint(odd_squares)\n\n# Output: {1: 1, 3: 9, 5: 25, 7: 49, 9: 81}<\/pre><\/div>\n\n\n\n<\/span>Built-in Functions with Dictionary<\/span><\/h3>\n\n\n\nThere are also some built-in functions you can use with a dictionary.<\/p>\n\n\n\n
- all(): <\/strong>Return True if all keys of the dictionary are true (or if the dictionary is empty).<\/li>
- any(): <\/strong>Return True if any key of the dictionary is true. If the dictionary is empty, return False.<\/li>
- len(): <\/strong>Return the length (the number of items) in the dictionary.<\/li>
- cmp(): <\/strong>Compares items of two dictionaries.<\/li>
- sorted(): <\/strong>Return a new sorted list of keys in the dictionary.<\/li><\/ol>\n\n\n\n
Let’s check some examples.<\/p>\n\n\n\n
squares = {1: 1, 3: 9, 5: 25, 7: 49, 9: 81}<\/pre>\n\n\n\nHow to find the length of the dictionary (number of items in the dictionary.)<\/strong><\/p>\n\n\n\nprint(len(squares)) # Output: 5<\/pre>\n\n\n\nHow to sort the items in the dictionary by key?<\/strong><\/p>\n\n\n\nprint(sorted(squares)) # Output: [1, 3, 5, 7, 9]<\/pre>\n\n\n\nOther Python Dictionary Tutorials:<\/strong><\/p>\n\n\n\n