Python - Add Dictionary Items

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Using the Operator

The "[]" operator (used to access value mapped to a dictionary key) is used to update an existing key-value pair as well as add a new pair.

Syntax

dict["key"] = val

If the key is already present in the dictionary object, its value will be updated to val. If the key is not present in the dictionary, a new key-value pair will be added.

Example

In this example, the marks of "Laxman" are updated to 95.

marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}
print ("marks dictionary before update: ", marks)
marks['Laxman'] = 95
print ("marks dictionary after update: ", marks)

It will produce the following output −

marks dictionary before update: {'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49}
marks dictionary after update: {'Savita': 67, 'Imtiaz': 88, 'Laxman': 95, 'David': 49}

Example

However, an item with 'Krishnan' as its key is not available in the dictionary, hence a new key-value pair is added.

marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}
print ("marks dictionary before update: ", marks)
marks['Krishan'] = 74
print ("marks dictionary after update: ", marks)

It will produce the following output −

marks dictionary before update: {'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49}
marks dictionary after update: {'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49, 'Krishan': 74}

Using the update() Method

You can use the update() method in dict class in three different ways:

Update with Another Dictionary

In this case, the update() method's argument is another dictionary. Value of keys common in both dictionaries is updated. For new keys, key-value pair is added in the existing dictionary

Syntax

d1.update(d2)

Return value

The existing dictionary is updated with new key-value pairs added to it.

Example

marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}
print ("marks dictionary before update: \n", marks)
marks1 = {"Sharad": 51, "Mushtaq": 61, "Laxman": 89}
marks.update(marks1)
print ("marks dictionary after update: \n", marks)

It will produce the following output −

marks dictionary before update:
{'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49}
marks dictionary after update:
{'Savita': 67, 'Imtiaz': 88, 'Laxman': 89, 'David': 49, 'Sharad': 51, 'Mushtaq': 61}

Update with Iterable

If the argument to update() method is a list or tuple of two item tuples, an item each for it is added in the existing dictionary, or updated if the key is existing.

Syntax

d1.update([(k1, v1), (k2, v2)])

Return value

Existing dictionary is updated with new keys added.

Example

marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}
print ("marks dictionary before update: \n", marks)
marks1 = [("Sharad", 51), ("Mushtaq", 61), ("Laxman", 89)]
marks.update(marks1)
print ("marks dictionary after update: \n", marks)

It will produce the following output −

marks dictionary before update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49}
marks dictionary after update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 89, 'David': 49, 'Sharad': 51, 'Mushtaq': 61}

Update with Keyword Arguments

Third version of update() method accepts list of keyword arguments in name=value format. New k-v pairs are added, or value of existing key is updated.

Syntax

d1.update(k1=v1, k2=v2)

Return value

Existing dictionary is updated with new key-value pairs added.

Example

marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}
print ("marks dictionary before update: \n", marks)
marks.update(Sharad = 51, Mushtaq = 61, Laxman = 89)
print ("marks dictionary after update: \n", marks)

It will produce the following output −

marks dictionary before update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49}
marks dictionary after update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 89, 'David': 49, 'Sharad': 51, 'Mushtaq': 61}

Using the Unpack Operator

The "**" symbol prefixed to a dictionary object unpacks it to a list of tuples, each tuple with key and value. Two dict objects are unpacked and merged together and obtain a new dictionary.

Syntax

d3 = {**d1, **d2}

Return value

Two dictionaries are merged and a new object is returned.

Example

marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}
print ("marks dictionary before update: \n", marks)
marks1 = {"Sharad": 51, "Mushtaq": 61, "Laxman": 89}
newmarks = {**marks, **marks1}
print ("marks dictionary after update: \n", newmarks)

It will produce the following output −

marks dictionary before update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49}
marks dictionary after update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 89, 'David': 49, 'Sharad': 51, 'Mushtaq': 61}

Using the Union Operator (|)

Python introduces the "|" (pipe symbol) as the union operator for dictionary operands. It updates existing keys in dict object on left, and adds new key-value pairs to return a new dict object.

Syntax

d3 = d1 | d2

Return value

The Union operator return a new dict object after merging the two dict operands

Example

marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}
print ("marks dictionary before update: \n", marks)
marks1 = {"Sharad": 51, "Mushtaq": 61, "Laxman": 89}
newmarks = marks | marks1
print ("marks dictionary after update: \n", newmarks)

It will produce the following output −

marks dictionary before update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49}
marks dictionary after update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 89, 'David': 49, 'Sharad': 51, 'Mushtaq': 61}

Using "|=" Operator

The "|=" operator is an augmented Union operator. It performs in-place update o n the dictionary operand on left by adding new keys in the operand on right, and updating the existing keys.

Syntax

d1 |= d2

Example

marks = {"Savita":67, "Imtiaz":88, "Laxman":91, "David":49}
print ("marks dictionary before update: \n", marks)
marks1 = {"Sharad": 51, "Mushtaq": 61, "Laxman": 89}
marks |= marks1
print ("marks dictionary after update: \n", marks)

It will produce the following output −

marks dictionary before update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 91, 'David': 49}
marks dictionary after update:
 {'Savita': 67, 'Imtiaz': 88, 'Laxman': 89, 'David': 49, 'Sharad': 51, 'Mushtaq': 61}