20 Python Dictionary Interview Questions and Answers

Python Dictionary is a data structure that allows you to store data in the form of key-value pairs. It is a mutable data type, which means that you can add, remove, and update elements in a dictionary. When applying for a position that requires knowledge of Python, you may be asked questions about dictionaries during your job interview. In this article, we review some of the most common questions about Python dictionaries and how you should answer them.

Python Dictionary Interview Questions and Answers

Here are 20 commonly asked Python Dictionary interview questions and answers to prepare you for your interview:

1. What is the usage of a dictionary in Python?

A dictionary is a data structure in Python that is used to store data in the form of key-value pairs. A dictionary can be used to store data in a variety of ways, such as a list of items, a list of prices, a list of addresses, etc.

2. How do you create a dictionary in Python?

You can create a dictionary in Python by using the dict() function. This function takes in a list of key-value pairs and returns a dictionary object.

3. Can you explain what a dictionary lookup is in Python?

A dictionary lookup is when you use a key to look up a value in a dictionary. For example, if you have a dictionary that contains information about countries, you could use the country’s name as the key to look up its population.

4. What’s the difference between a dict and a list in Python?

Dictionaries are unordered, mutable data structures that store mappings of keys to values. Lists are ordered, mutable data structures that store a sequence of values. The main difference between the two is that a dict is used to store key-value pairs, while a list is used to store a sequence of values.

5. Is it possible to add a key-value pair to an empty dictionary? If yes, then how?

Yes, it is possible to add a key-value pair to an empty dictionary. You can do this by using the update() method. The update() method takes a dictionary as an argument and adds the key-value pairs from that dictionary to the original dictionary.

6. Is it possible to remove a key from a dictionary if it’s not empty? If yes, then how?

Yes, it is possible to remove a key from a dictionary if it’s not empty. This can be done by using the del keyword.

7. What does the “in” operator do in Python?

The “in” operator is used to check if a given key is present in a dictionary. If the key is present, then the operator will return “True”, otherwise it will return “False”.

8. What is the maximum number of items that a Dictionary can hold?

There is no maximum number of items that a Dictionary can hold. A Dictionary can hold as many items as you want, as long as you have the memory to store them.

9. What are some ways to achieve thread-safety when using dictionaries?

One way to achieve thread-safety when using dictionaries is to use a lock. This will allow only one thread to access the dictionary at a time, which will prevent any race conditions from occurring. Another way to achieve thread-safety is to use a thread-safe dictionary implementation, such as the one provided by the Python standard library.

10. Why is a dictionary preferred over a list in Python?

Dictionaries are preferred over lists in Python for a number of reasons. Dictionaries are more efficient when it comes to storing and retrieving data, and they are also more flexible. With a dictionary, you can store data of any type, whereas with a list you can only store data of one type. Additionally, dictionaries are unordered, which means you can’t index them like you can with a list.

11. What do you understand about hash tables?

Hash tables are a data structure that is used to store key-value pairs. In a hash table, the keys are used to calculate a hash, which is then used to index into an array. The value is then stored at that index in the array. Hash tables are used because they provide constant time access to the data, regardless of the size of the data set.

12. Is it possible to convert a dictionary to a tuple in Python? If yes, then how?

Yes, it is possible to convert a dictionary to a tuple in Python. This can be done by using the items() method to return a list of key-value pairs, and then using the tuple() function to convert that list into a tuple.

13. What are some ways to access values in a dictionary?

There are a few ways to access values in a dictionary. One way is to use the key to index into the dictionary and retrieve the value. Another way is to use the get() method, which will return the value associated with a given key, or a default value if the key is not present in the dictionary. Finally, you can also use the values() method to return a list of all the values in the dictionary.

14. What is the best way to check for emptiness or existence of a dictionary in Python?

The best way to check for the existence of a key in a dictionary is to use the in keyword. This will return True if the key exists in the dictionary and False if it does not. To check for emptiness, you can use the len() function. This will return the number of items in the dictionary. If the dictionary is empty, it will return 0.

15. What are iterables and why are they important?

Iterables are important because they allow you to loop through data structures like lists and dictionaries. This means that you can access each element in the data structure one by one, which can be very useful when you are trying to extract specific information or perform certain operations.

16. What is the purpose of the collections module in Python?

The collections module in Python is a module that provides specialized data structures that are not available in the standard library. These data structures can be very useful in certain situations, such as when you need to store data in a way that is different from a list or a tuple.

17. What is the best way to sort a dictionary by its keys?

The best way to sort a dictionary by its keys is to use the sorted() function. This function will take a dictionary as an input and return a list of tuples, with each tuple containing a key and its corresponding value.

18. What happens if two dictionary keys have the same value?

If two dictionary keys have the same value, the key that was added last will overwrite the key that was added first.

19. What are defaultdicts and Counters?

Defaultdicts are a type of dictionary that allow you to specify a default value for keys that do not exist. Counters are a type of dictionary that keep track of how many times a key is added.

20. What is the best way to merge two dictionaries in Python?

The best way to merge two dictionaries in Python is to use the update() method. This method will update the first dictionary with the contents of the second dictionary. If there are any key collisions, the second dictionary’s values will overwrite the values from the first dictionary.