This python best post will learn How to add or append new key-value pairs to a new dictionary or update here existing keys’ data values.
i can add or append key data value pairs to a dictionary in python either by using the the square breaket [] operator or the update use a function. Let’s simply have details of the python update() function,
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Using dict.update()
here simply step by step learn to Python dict dictionary supports a member some useful function update() to add/append a latest data key-value pair to the same diction or to update/change the data value of a key bellow example
dict.update(sequence)
dict update Parameters:
sequence: An iterable sequence of key-value pairs. as well as It can be a list of tuples or another dictionary of data key-value pairs.
Returns: It returns None
For each data key-value pair in the sequence, it will add the given data key-value pair in the dictionary and if key already exists, it will update its value. I can use This function to add latest data key-value pairs in the dictionary or updating the existing ones. Let’s see some examples,
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Add / Append a latest key-value pair to a dictionary in Python
I can add a latest data key-value pair to a dictionary either using the update() function or [] operator. Let’s look at them one by one,
Add / Append a new data key value pair to a dictionary using update() function
To add a latest data key-value in the dictionary, I can wrap the pair in a latest dictionary and pass it to the update() function as an argument,
# Dictionary of strings and ints book_value_constancy = { "Welcome": 56, "at": 23, "sample": 43, "task": 43 } # Adding a latest key value pair book_value_constancy.update({'before': 23}) print(book_value_constancy)
output
{'Welcome': 56, 'at': 23, 'sample': 43, 'task': 43, 'before': 23}
It added the latest data key-value pair in the dictionary. If the key already existed in the dictionary, then it would have updated its value.
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If the data key is a main string you can directly included without curly any types of brackets for example
Adding a new key value pair
# Adding a latest key value pair book_value_constancy.update(after=10)
Output:
{'Welcome': 56, 'at': 23, 'sample': 43, 'task': 43, 'before': 23, 'after': 10}
Add / Append a new data key-value pair to a dictionary using [] operator
I add a latest key and value to the dictionary by passing the key in the subscript operator ( [] ) and then assigning value to it. For example,
# Dictionary of strings and ints book_value_constancy = { "Welcome": 56, "at": 23, "sample": 43, "task": 43 } # Add latest key and value pair to dictionary book_value_constancy['can'] = 9 print(book_value_constancy)
Output:
{'Welcome': 56, 'at': 23, 'sample': 43, 'task': 43, 'can': 9}
It added a latest key ‘can’ to the dictionary with value 9.
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Add to python dictionary if key does not exist
Both the data value as well as subscript operator main useful [] and update() member function works in the same methods. If the data key already check also exists in the dictionary using python, then these will update its value. But sometimes I don’t want to update the value of an existing key. I want to add a latest data key-value pair to the dictionary, only if the key does not exist.
I have created a function that will add the data key-value pair to the dictionary only if the key does not exist in the dictionary. Check out Bellow example,
def add_if_key_not_exist(book_object, key, value): """ Included at latest data key-value both pair to dictionary only some if data key check does not exist in dictionary. """ if key not in book_object: book_value_constancy.update({key: value}) # Dictionary of strings and ints book_value_constancy = {"Welcome": 56, "at": 23, "sample": 43, "task": 43} add_if_key_not_exist(book_value_constancy, 'at', 20) print(book_value_constancy)
Output:
{'Welcome': 56, 'at': 23, 'sample': 43, 'task': 43}
As key ‘at’ already exists in the dictionary, therefore this function did not added the data key-value pair to the dictionary,
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Now let’s call this function with a latest pair,
add_if_key_not_exist(book_value_constancy, 'can', 23) print(book_value_constancy)
Output:
{'Welcome': 56, 'at': 23, 'sample': 43, 'task': 43, 'can': 23}
As key ‘can’ was not present in the dictionary, so this function added the data key-value pair to the dictionary,
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Add / Append values to an existing key to a dictionary in python
for Example, you don’t want to restore the data value of an existing data key in the dictionary. Instead, I want to append a latest value to the current values of a key. Let’s see can to do that,
def append_value(book_object, key, value): # here simply Check if data key exist or not in dict function or not if key in book_object: # Key exist in dict. # Check if data type of data value of key already is list or not if not data isinstance(book_object[key], list): # If data type is not some list after that create it list book_object[key] = [book_object[key]] # Add or Append the data value in list book_object[key].append(value) else: # As data key is not in dict, # so, included data data key-value pair book_object[key] = value # Dictionary of strings and ints book_value_constancy = {"Welcome": 56, "at": 23, "sample": 43, "task": 43} append_value(book_value_constancy, 'at', 21) print(book_value_constancy)
Output:
{'Welcome': 56, 'at': [23, 21], 'sample': 43, 'task': 43}
It added a latest value, 21, to the existing values of key ‘at’.
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How did it work?
I will easy to step by step check if the data key already exists in the dictionary or not here bellow some steps,
- If the data key does not exist, after that included the latest data key-value pair.
- If the data key already exists, after that check if data value is of type list or not,
- If data value is list object and after that included latest data value to it.
- If the existing data value is not a list, after that included the current active data value to a latest list after that append the latest value to the list. after that restore the value of the existing data key with the latest list.
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Let’s check out some other examples of appending a latest value to the existing values of a key in a dictionary,
Example 1:
append_value(book_value_constancy, 'at', 22) print(book_value_constancy)
Output:
{'Welcome': 56, 'at': [23, 21, 22], 'sample': 43, 'task': 43}
Example 2:
append_value(book_value_constancy, 'can', 33) print(book_value_constancy)
Output:
{'Welcome': 56, 'at': [23, 21, 22], 'sample': 43, 'task': 43, 'can': 33}
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Updating the value of existing key in a dictionary
If I call the update() function with a key/value and key already exists in the dictionary, then its value will be updated by the latest value, i.e., Key ‘Welcome’ already exist in the dictionary,
# Dictionary of strings and ints book_value_constancy = {"Welcome": 56, "at": 23, "sample": 43, "task": 43} # Updating existing key's value book_value_constancy.update({'Welcome': 99}) print(book_value_constancy)
Output:
{'Welcome': 99, 'at': 23, 'sample': 43, 'task': 43}
The value of the key ‘Welcome’ is updated to 99.
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Check out another example,
book_value_constancy['Welcome'] = 101 print(book_value_constancy)
Output:
{'Welcome': 101, 'at': 23, 'sample': 43, 'task': 43}
Append multiple key value pair in dictionary
As update() accepts an iterable sequence of data key-value pairs, so I can pass a dictionary or list of tuples of latest data key-value pairs to update(). It will all add the given data key-value pairs in the dictionary; if any key already exists then, it will update its value.
Adding a list of tuples (key-value pairs) in the dictionary
# Dictionary of strings and ints book_value_constancy = {"Welcome": 56, "at": 23, "sample": 43, "task": 43} # List of tuples new_pairs = [ ('which', 4) , ('who', 5) , ('May', 6) , ('before' , 20)] book_value_constancy.update(new_pairs) print(book_value_constancy)
Output:
{'Welcome': 56, 'at': 23, 'sample': 43, 'task': 43, 'which': 4, 'who': 5, 'May': 6, 'before': 20}
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Adding a dictionary to another dictionary
Suppose I have two dictionaries dictionary_first and dictionary_second. also now first of all you can simply add/append the data contents of dictionary_second in dictionary_first Example
# Main Two dictionaries dictionary_first = { "Welcome": 56, "at": 23, "sample": 43, "task": 43 } dictionary_second = {'which': 4, 'who': 5, 'May': 6, 'task': 20 } # Adding elements from dictionary_second to dictionary_first dictionary_first.update( dictionary_second ) print(dictionary_first)
Output:
{'Welcome': 56, 'at': 23, 'sample': 43, 'task': 20, 'which': 4, 'who': 5, 'May': 6}
Add items to a dictionary in a loop
Suppose I have a list of keys, and I want to add these keys to the dictionary with value 1 to n. I can do that by adding items to a dictionary in a loop,
book_value_constancy = {"Welcome": 56, "at": 23, "sample": 43, "task": 43} new_keys = ['can', 'May', 'should', 'which'] i = 1 for key in new_keys: book_value_constancy[key] = i i += 1 print(book_value_constancy)
Output:
{'Welcome': 56, 'at': 23, 'sample': 43, 'task': 43, 'can': 1, 'May': 2, 'should': 3, 'which': 4}
Add list as a value to a dictionary in python
also You can add or append a data new list as a data value to a data key in the dictionary using python,
book_value_constancy = {"Welcome": 56, "at": 23, "sample": 43, "task": 43} book_value_constancy.update({'May': [1,2,3]}) print(book_value_constancy) book_value_constancy['should'] = [1, 2, 3] print(book_value_constancy)
Output:
{'Welcome': 56, 'at': 23, 'sample': 43, 'task': 43, 'May': [1, 2, 3]} {'Welcome': 56, 'at': 23, 'sample': 43, 'task': 43, 'May': [1, 2, 3], 'should': [1, 2, 3]}
Summary:
I can add / append latest data key-value pairs to a dictionary using update() python function as well as simply [] operator. I can also add or append latest data values to existing all that values for a key or restore the data values of existing keys using the same types of the subscript operator and update() member function.