Python dict update example

Python Dictionary update()

The update() method updates the dictionary with the elements from another dictionary object or from an iterable of key/value pairs.

Example

marks = internal_marks = 
marks.update(internal_marks)
 print(marks) # Output:

Syntax of Dictionary update()

update() Parameters

The update() method takes either a dictionary or an iterable object of key/value pairs (generally tuples).

If update() is called without passing parameters, the dictionary remains unchanged.

Return Value from update()

update() method updates the dictionary with elements from a dictionary object or an iterable object of key/value pairs.

It doesn’t return any value (returns None ).

Example 1: Working of update()

d = d1 = # updates the value of key 2 
d.update(d1)
 print(d) d1 = # adds element with key 3 
d.update(d1)
 print(d)

Note: The update() method adds element(s) to the dictionary if the key is not in the dictionary. If the key is in the dictionary, it updates the key with the new value.

Example 2: update() When Tuple is Passed

dictionary = 
dictionary.update([('y', 3), ('z', 0)])
 print(dictionary)

Here, we have passed a list of tuples [(‘y’, 3), (‘z’, 0)] to the update() function. In this case, the first element of tuple is used as the key and the second element is used as the value.

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Python Dictionary update()

In this article discuss how to use the update() method of the dict class in python and then we will look at some examples of the update() function.

dict.update() Syntax:

In python, dict class provides a function to update the values of keys i.e.

• • • Sequence: An optional iterable sequence of key-value pairs. It can be another dictionary or list of tuples etc.

    Return Value:

    Frequently Asked:

    update() function accepts an iterable sequence of key-value pairs (dictionary or list of tuples) as an argument and then updates the values of keys from the sequence to the dictionary.

    If any key is present in sequence argument but not exist in the dictionary, then it adds the key in the dictionary along with the given value. Whereas, if the update() function is called without any argument, then it does not modify the dictionary.

    Let’s understand more with some examples,

    Examples of dict.update()

    Update value of a key in a dictionary in python

    To update the value of an existing key in the dictionary, just create a temporary dictionary containing the key with new value and then pass this temporary dictionary to the update() function,

    # Dictionary of string and int word_freq = < "Hello": 56, "at": 23, "test": 43, "this": 78 ># python dictionary update value of key word_freq.update() print('Modified Dictionary:') print(word_freq)

    It updated the value of the key ‘at’ in the dictionary.

    The behavior of update() function, when passed a key that doesn’t exist in the dictionary

    If we pass a key-value pair in the update() function and the given key does not exist in the dictionary, then it adds that key in the dictionary with the given value. For example,

    # Dictionary of string and int word_freq = < "Hello": 56, "at": 23, "test": 43, "this": 78 ># if key does not exist then upate(0 function # will add a new key in dict with given value word_freq.update() print('Modified Dictionary:') print(word_freq)

    As key ‘here’ does not exist in the dictionary, so update() function added that too the dictionary.

    Update values of multiple keys in a dictionary using update() function

    If we want to update the values of multiple keys in the dictionary, then we can pass them as key-value pairs in the update() function. To bind keep multiple key-value pairs together, either we can use a list of tuples or we can create a temporary dictionary.

    # Dictionary of string and int word_freq = < "Hello": 56, "at": 23, "test": 43, "this": 78 ># Update values of multiple keys in dictionary word_freq.update() print('Modified Dictionary:') print(word_freq)

    Here we passed 3 key-value pairs to the update() function. Out of these 3, the 2 keys exist in the dictionary and the third key i.e. ‘here’ doesn’t exist in the dictionary. So, it updated the values of 2 keys that already exist in the dictionary and added the third one in the dictionary.

    Update the key name in dictionary using update() function

    We can not change the key in a dictionary. So if we want to change the key in the dictionary then we need to delete the current key-value pair from the dictionary and add a new key in the dictionary with the same value.

    # Dictionary of string and int word_freq = < "Hello": 56, "at": 23, "test": 43, "this": 78 >#Update key name in python dictionary value = word_freq.pop('at') word_freq.update() print('Modified Dictionary:') print(word_freq)

    It gave an effect that we have updated the key name from ‘at’ to ‘where’. But actually, we fetched the value of key ‘at’, then deleted that entry from the dictionary and then added a new key ‘where’ in the dictionary with the same value.

    So, this is how we can use the update() method of the dict class in python to add or update values.

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    Python Dictionary update() Method

    The update() method inserts the specified items to the dictionary.

    The specified items can be a dictionary, or an iterable object with key value pairs.

    Syntax

    Parameter Values

    Parameter	Description
    iterable	A dictionary or an iterable object with key value pairs, that will be inserted to the dictionary

    

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    Python Dictionary Update

    In this tutorial, you will learn how to update a dictionary in Python. You will learn how to add new key-value pairs to a dictionary and how to update existing items in a dictionary.

    Dictionary is a mutable data type in Python. It means that we can change the contents of a dictionary after it has been created. We can add or update key-value pairs in a dictionary.

    

  • update() method
    1. Example 1
    2. Example 2
    3. Example 3
    4. Example 4
    5. Example 5
  • Update if Key Exists
  • Alternative to update()

  update() Method in Dictionary

  The update() method in Python dictionary is used to add or update key-value pairs in a dictionary.

  Example 1: Add new key-value pairs to a dictionary

  If the key is not present in the dictionary, then the update() method adds the key-value pair to the dictionary.

  Key in the dictionary below so, the item will be added

  dict1 = dict2 = print("Before update:", dict1) # add key-value pairs from dict2 to dict1 dict1.update(dict2) print("After update:", dict1)

  Before update: After update:

  Example 2: Update existing items in a dictionary

  If the key is already present in the dictionary, then the update() method updates the value of the key with the new value.

  Key in the dictionary below so, the item will be updated

  dict1 = dict2 = print("Before update:", dict1) # update value of key 'b' in dict1 dict1.update(dict2) print("After update:", dict1)

  Before update: After update:

  Example 3: Add new key-value pairs to a dictionary using iterable

  We can also add new key-value pairs to a dictionary using an iterable of key-value pairs (list of tuples).

  Key in the dictionary below so, the item will be added

  dict1 = print("Before update:", dict1) # add key-value pairs from iterable to dict1 dict1.update([('c', 3), ('d', 4)]) print("After update:", dict1)

  Before update: After update:

  Example 4: Update and add existing items in a dictionary using iterable

  We can also update existing items in a dictionary using an iterable of key-value pairs (list of tuples).

  Key in the dictionary below so, the item will be updated

  dict1 = print("Before update:", dict1) # update value of key 'b' in dict1 dict1.update([('b', 3), ('c', 4)]) print("After update:", dict1)

  Before update: After update:

  Example 5: Update and add items in a dictionary using keyword arguments

  We can also update existing items in a dictionary using keyword arguments.

  Key in the dictionary below so, the item will be updated

  dict1 = print("Before update:", dict1) # update value of key 'b' in dict1 dict1.update(b=3, c=4) print("After update:", dict1)

  Before update: After update:

  Python Dictionary Update if Key Exists

  To update a value in a dictionary only if the key exists, we can use an if-else statement in python to check if the key exists in the dictionary.

  If the key exists, then we update the value of the key. Otherwise, we do nothing.

  dict1 = print("Before update:", dict1) # update value of key 'b' in dict1 if 'b' in dict1: dict1['b'] = 3 print("After update:", dict1)

  Before update: After update:

  Alternative to Python Dictionary Update

  You can also update an item of a dictionary using the [ ] and = operators.

  To update an item, we first access the item using the key and then assign a new value to it.

  Let’s see an example to understand this.

  dict1 = print("Before update:", dict1) # update value of key 'b' in dict1 dict1['b'] = 3 print("After update:", dict1)

  Before update: After update:

  Frequently Asked Questions

  1. Can Python dictionary be modified? Yes, the Python dictionary is mutable. We can add, update, and delete items from a dictionary.
  2. How do you update a dictionary in Python? Use the update() method and pass the dictionary or iterable of key-value pairs as an argument (You can also use assignment operator). If the key is already present in the dictionary, then the update() method updates the value of the key with the new value. If the key is not present in the dictionary, then the update() method adds the key-value pair to the dictionary.
  3. Does dictionary update overwrite? Yes, if the key is already present in the dictionary, then the update() method updates the value of the key with the new value.

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