How to Add Key-Value Pairs to a Dictionary in Python
Using dict.update()
Contents
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.
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,
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,
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’.
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}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.
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}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.
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