How does Python iterate over dictionary keys in a 'for' loop?

General Discussions
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1

How does Python recognize that it needs only to read the key from the dictionary when using a ‘for’ loop to python iterate over dictionary?

In the following code:

d = {'x': 1, 'y': 2, 'z': 3}

for key in d:
    print(key, 'corresponds to', d[key])

Is key a special keyword, or is it simply a variable? How does Python understand that it should iterate over the keys of the dictionary in this case?

2

Wishing you a great day! @smrity.maharishsarin

In Python, when you iterate over a dictionary using a for loop, it automatically loops through the dictionary’s keys by default. For example, in for key in d, the variable key is just a regular variable (not a special keyword) that represents each key during the iteration.

Internally, Python uses the dictionary’s __iter__ method to return an iterator, which then yields the keys one by one in each iteration.

Hope this clears up your query! :blush:

Thank you!

3

Using .keys() method to iterate over dictionary: Although Python will automatically iterate over the keys of a dictionary in a for loop, you can explicitly iterate over the keys by using the keys() method, like this: for key in d.keys(): print(key, ‘corresponds to’, d[key])

This way, it’s clear that you’re specifically iterating over the keys. However, the behavior remains the same, as the default iteration method for dictionaries is to return the keys.

4

Hello everyone,

If you’re looking to iterate over a dictionary in Python and access both the keys and their corresponding values in one step, the .items() method is the way to go! This method returns key-value pairs, making your code more concise and easier to understand.

Here’s an example:

for key, value in d.items():  
    print(key, 'corresponds to', value)

By using .items(), you avoid referencing the dictionary twice, which simplifies the process and makes your code cleaner.

Hope this helps!

Thank you.