How to Merge Two Dictionaries In Python?

In Python, you can merge two dictionaries by using the update() method. This method takes another dictionary as an argument and adds all key-value pairs from that dictionary into the original dictionary. If there are any duplicate keys, the values from the argument dictionary will overwrite the values in the original dictionary.

Here is an example of how to merge two dictionaries in Python:

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dict1 = {'a': 1, 'b': 2}
dict2 = {'b': 3, 'c': 4}

dict1.update(dict2)

print(dict1)

This will output: {'a': 1, 'b': 3, 'c': 4}.

Alternatively, you can also use the double asterisk ** operator to merge two dictionaries:

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dict1 = {'a': 1, 'b': 2}
dict2 = {'b': 3, 'c': 4}

merged_dict = {**dict1, **dict2}

print(merged_dict)

This will produce the same output: {'a': 1, 'b': 3, 'c': 4}.

What is the best practice for merging dictionaries in Python?

One common way to merge dictionaries in Python is by using the update() method. This method adds all elements from one dictionary to another, overwriting the values of any keys that already exist. Here is an example:

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dict1 = {'a': 1, 'b': 2}
dict2 = {'b': 3, 'c': 4}

dict1.update(dict2)

print(dict1)

Output:

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{'a': 1, 'b': 3, 'c': 4}

Alternatively, you can use the dictionary unpacking operator (**), which was introduced in Python 3.5:

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dict1 = {'a': 1, 'b': 2}
dict2 = {'b': 3, 'c': 4}

merged_dict = {**dict1, **dict2}

print(merged_dict)

Output:

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{'a': 1, 'b': 3, 'c': 4}

Both methods will merge the dictionaries in a similar way, but the dictionary unpacking method is more concise and often preferred for its readability.

How to merge dictionaries in Python using dictionary comprehension?

You can merge dictionaries in Python using dictionary comprehension by creating a new dictionary that combines the key-value pairs of two or more dictionaries.

Here is an example of how to merge two dictionaries using dictionary comprehension:

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dict1 = {'a': 1, 'b': 2}
dict2 = {'c': 3, 'd': 4}

merged_dict = {key: value for d in [dict1, dict2] for key, value in d.items()}

print(merged_dict)

In this example, the merged_dict dictionary will contain the key-value pairs from both dict1 and dict2. The dictionary comprehension iterates over each dictionary in the list [dict1, dict2] and then iterates over each key-value pair in that dictionary, adding them to the merged_dict.

How to merge dictionaries in Python with custom merge strategies?

To merge dictionaries in Python with custom merge strategies, you can write a function that takes the dictionaries to merge as input along with the custom merge strategy and returns the merged dictionary according to the custom strategy.

Here's an example of merging dictionaries with a custom strategy that concatenates values of duplicate keys:

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def merge_dicts(dict1, dict2, merge_strategy):
    merged_dict = dict(dict1)
    
    for key, value in dict2.items():
        if key in merged_dict:
            merged_dict[key] = merge_strategy(merged_dict[key], value)
        else:
            merged_dict[key] = value
    
    return merged_dict

def custom_merge_strategy(val1, val2):
    return val1 + val2

dict1 = {'a': 1, 'b': 2}
dict2 = {'a': 3, 'c': 4}

merged_dict = merge_dicts(dict1, dict2, custom_merge_strategy)
print(merged_dict)

In this example, the merge_dicts function takes two dictionaries dict1 and dict2, along with a custom merge strategy function custom_merge_strategy. The custom_merge_strategy function takes two values and concatenates them. The merge_dicts function then merges the dictionaries dict1 and dict2 using the custom merge strategy and returns the merged dictionary.

You can customize the custom_merge_strategy function to implement different merge strategies based on your requirements.

How to merge dictionaries in Python using the "dict" constructor?

To merge dictionaries in Python using the "dict" constructor, you can create a new dictionary by passing the key-value pairs of the dictionaries you want to merge as arguments to the constructor. Here's an example:

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dict1 = {
    'a': 1,
    'b': 2
}

dict2 = {
    'b': 3,
    'c': 4
}

merged_dict = dict(dict1, **dict2)

print(merged_dict)

Output:

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{'a': 1, 'b': 3, 'c': 4}

In this example, we first declare two dictionaries, dict1 and dict2. We then merge these dictionaries by passing them as arguments to the dict constructor and using the ** operator to unpack the second dictionary. The resulting merged_dict contains key-value pairs from both input dictionaries.