Dictionary looping speed comparison

Hi Pythonistas, Today we are going to analyze the performance of different ways of accessing the dictionary in Python.

Let's consider the example

Using loop the dict and access using key

def looping_using_key():
    data = {str(i): i for i in range(20)}
    for key in data:
        a = data[key]

Using items method

def looping_using_items():
    data = {str(i): i for i in range(20)}
    for key, value in data.items():
        a = value

Analysis using the timeit module

time_taken = timeit.timeit(looping_using_key, number=10000)
print("Time taken using key: ", time_taken)

time_taken = timeit.timeit(looping_using_items, number=10000)
print("Time taken using item: ", time_taken)

Output

Time taken using key:  0.04307970999798272

Time taken using item:  0.039506489996711025

Why

In the first method, we are accessing the dictionary using a key so for every check, we need to find the hash of the key and fetch the item.  

In the second method, the items method returns the list of tuple of key-value pair. So there is additional lookup. So it faster

Bonus

If we need only the values we have the values method this is faster than the items method.

Using values method

def looping_using_values():
    data = {str(i): i for i in range(20)}
    for value in data.values():
        a = value

time_taken = timeit.timeit(looping_using_values, number=10000)
print("Time taken using value: ", time_taken)

Time taken using value:  0.033650106997811235

Tip

Use items, values methods for looping the data in the dictionary.

Hope you have learned something from this post. Please share your suggestion with afsal@parseltongue.co.in