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Cover image for #Day27 - Fastest Way to Combine Dictionaries

#Day27 - Fastest Way to Combine Dictionaries

Rahul Banerjee
Comp Eng Student @uoft | My opinions are my own Add me on LinkedIn: https://www.linkedin.com/in/rahulbanerjee2699/
Originally published at realpythonproject.com ・2 min read

We know the fastest way to combine lists. Today we will try to find the fastest way to combine dictionaries

We will be considering the following ways

  • Using a for loop
  • Using the update() method
  • Using the ChainMap Function
  • Using the unpacking operator
  • Using the pipe operator ( | )
  • Using the (|=) operator

How are we going to measure the performance?

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We have a couple of dictionaries with 1000 key-value pairs in each dictionary. We will update function func to perform the different combination methods. The function will be called 100 times and we will print the average run time.

Using a for loop

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We simply iterate over the second dictionary and add its elements to the first dictionary.
Below is the output

On average, it took 6.765522999558016e-05 seconds
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Using the update method

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Similar to the for loop approach, the first dictionary is updated. The elements of the second dictionary are added to the first dictionary. If there is a common key present, the value for the key in the first dictionary will be overwritten by that of the second dictionary.

On average, it took 2.554959000008239e-05 seconds
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Using the ChainMap Function

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Unlike the previous two approaches, a new dictionary is created and the original dictionaries are not updated. Below is the output

On average, it took 9.942399992723949e-07 seconds
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Using the unpacking operator

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In this approach as well, we create a new dictionary. The original dictionaries are not updated.
Below is the output

On average, it took 7.01560299967241e-05 seconds
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Using the | operator

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In Python 3.9, the pipe operator was introduced to combine dictionaries. Below is the output

On average, it took 5.5255000000000026e-05 seconds
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Using the |= operator

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Along with the | operator, the |= operator was introduced in Python 3.9. Below is the output

On average, it took 3.0259589999999983e-05 seconds
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Comparison

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The ChainMap() method seems to be the fastest

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