Interview Questions for Junior Python Developers

Are you preparing for a junior Python developer job interview? Let’s talk about potential Python questions you might encounter!

Python has gained an enormous amount of ground; it’s ranked as the most popular programming language on many sites. The number of people using this powerful language and the number of Python job offers on different platforms has (not surprisingly) also been steadily increasing.

The Popularity of Python

Python’s rise in popularity can be largely attributed to machine learning and data science. Nowadays, many companies are focusing on collecting data and using that data to optimize their business strategies. Python’s simplicity has made it the best choice for people who wanted to use this data but didn’t have a programming background. (Of course, lots of other fields use Python; you can also read more about why you should learn Python in 2021.)

Lately, the most popular Python jobs include data scientist, machine learning engineer, and backend engineer. All of these positions offer a great salary, which makes them quite competitive. Other Python jobs are hiring, too. You can also look at various Python job listings to get a good idea of what’s available.

Developer Jobs Require Interviews

It's great that you want to become a Python developer. This is one of the better career decisions you can make. However, you must remember that many people have made a similar choice. Fortunately, the world of programming is extremely spacious and will accept almost any number of new programmers; research shows that the demand for new developers will continue to grow for many years. So don’t worry that there’s no place for you!

However, this does not relieve you of the need for continuous improvement and development. You also have to be better than the other candidates for the position you are interested in – and demonstrate this during the interview process.

Since Python developer positions are so popular, you can expect some stiff competition. You’ll need to be well prepared and do your best. It’s worth knowing the topics that usually arise during Python job interviews. This way, you can be sure of your knowledge.

If you are a Python beginner who is just starting the language, you might be interested in our Python Basics course. It will teach you the foundations of the language. You’re given all the fundamentals; it will be up to you whether you want to go further and explore more complex topics and problems.

Common Python Interview Questions

Let’s go over some questions you might face when you are interviewing for a junior Python developer job. Junior positions are mostly where you’ll start your career. This is why the questions you will get asked tend to be simpler as well. Here are the topics you can expect to cover in your job interview:

1. Simple Loops

Loops are one of the most common code structures. They allow you to iterate on (go over and over) a data set and perform operations on it. Once you hit a certain condition, the loop stops. No matter what level of programmer you are, you’ll write loops. To learn more, see How to Write a For Loop in Python.

2. List Indexing and Slicing

Lists are used in Python for many tasks; knowing how to create and manipulate them is essential. In Python, lists can be indexed (i.e. finding a list element by its position in the list). A potential interview task could be ‘Use indexing to get the first, third, or last element in a list’.

It’s also good to know that Python supports negative indexing. A negative index is similar to a regular index, but starts with -1 (for the last element in the list), with indices getting smaller (e.g. decreasing to -2, -3, -4, etc.) as you get closer to the start of the list. This is a popular topic for junior developer job questions.

Another common question is the slicing. Slicing is essentially taking a smaller list out of the initial one by setting a starting and ending index. It is also possible to set a step value, which determines which elements to take between these indices. A step value of 1 picks every element, whereas a step value of 2 would pick alternate elements.

One of the more interesting applications of indexing and slicing is in external data science libraries like NumPy and pandas, which use the same indexing and slicing syntax.

Want to know more about other Python libraries? Check out our picks for the 13 Top Python Libraries and the Top 15 Python Libraries for Data Science.

3. Dictionaries

Just as lists and loops are used quite often in Python, so is the dictionary data structure. A question that asks you to calculate the frequency of random items or create a lookup structure that is fast to access is an ideal time to use a dictionary. You can think of a dictionary as a phone book; it works by key-value pairs. (In the case of a phone book, the key would be the person’s surname and given name; the value would be the phone number.) The key is easy to find, and then we can speedily access the value associated with it.

4. File Operations

As a backend developer or a data scientist, you will have to deal with different types of files. Hence, it is crucial to know how to read from or write to files using Python. You might get asked to read data from a file and draw some conclusions from it or to modify defective data in a file and save it. Python has built-in modules for all these tasks, but it is always beneficial to know the libraries that are used frequently in the area of your prospective job.

If you are curious about this topic and want to expand your knowledge, I recommend the interactive Data Processing with Python track. You will learn how to work with files of different types in Python.

5. String Operations

Another common Python task is to manipulate strings. You might get asked to find out if a certain text has a word or if any of the words repeat more than once in a string. Knowing how to use specific Python string functions is crucial to answering these questions. Python has text functions for making characters uppercase or lowercase, deleting certain characters or words from the text, or separating a long text into chunks using certain delimiters.  (Python includes some advanced string operations, such as the use of Regex. But since we are talking about junior positions, we won’t get into them here.)

6. Classes and Objects

The object-oriented programming paradigm is quite widely used for any kind of development job. So, it’s wise to be prepared for such questions. You might get asked to write a class for a provided data type and then write methods for this class. It is important to focus on the structure of the class, making it easily reusable and its methods clear.

In any developer job, you’ll be expected to write code that can be easily used by other programmers without them having to delve too deep into what happens in it. The same applies to classes. For example, if you have a class for a bank account and a method called “Transfer”, the user of this class would expect the method to actually mimic the transferring of money from one account to another. If it does something else (or anything extra), that should be clear from the context or from the comments.  (As we mentioned earlier, at  junior-level positions, more advanced topics like inheritance most likely won’t be discussed during the interview.)

Now You Know Junior Python Job Questions

We’ve talked about some common Python job interview questions and covered the topics used during real developer work. It is always a good idea to be prepared for job interviews, as you will definitely face one when applying to be a developer. Companies use interviews to weed out weaker applicants and find the ones that are right for the job.

The best way to be prepared for the interviews is to practice Python programming. If you don’t know where to look for practice questions, check out our Python practice set. (Find out what it's all about here.)

Of course, just solving questions is not in itself enough. A healthy mixture of practicing questions, writing code for your own projects, reading more about Python, and learning about the specific job you want are also important. I’d start with learning the best ways to practice Python.  It is also very important to note that learning any programming language is a constant endeavor. Since technology is improving rapidly each day, it is our duty as developers to stay informed about the new features and constantly improve ourselves.