# Python coding interview questions and Answers

Python is one of the programming languages that is known for its simplicity, readability, and its wide range of applications. A Python interview helps assess a candidate’s knowledge and skills in the Python programming language. A candidate has to prepare himself by thoroughly understanding the data structures, syntax, and OOP.

These Python interview questions help a jobseeker prepare for his interview:

## Python basic coding interview questions

**1. Write a program to print “Hello, World!”.**

By asking this question, interviewers aim to assess the candidate’s understanding of basic Python fundamentals. The difficulty level for this question is incredibly low.

**Sample answer: **To display “Hello World!” in Python, we can use the print function. This is the following code: print(‘Hello World!’)

**2. ****Write a program to check if a number is even or odd. **

An interviewer expects the candidate to demonstrate their knowledge of conditional statements and basic arithmetic operations.

**Sample answer: **I would use moderator in Python, denoted as ‘%’ I will then take the number as input and divide it by 2. If the remainder is 0, the number is even.

**3. ****Write a program to find the sum of all numbers in a list. **

The hiring manager expects the candidate to write clean and readable code as well as their problem-solving skills.

**Sample answer: **To find the sum of all numbers in a list, I would iterate through each element in the list using a for loop. The total sum can be generated as an output after running total of the numbers encountered.

**4. ****Write a program to find the largest number in a list. **

The interviewer assesses the candidate’s knowledge of loops and comparison operators. They expect the candidate to write a program that iterates through a list of numbers, compares them to find the largest value.

**Sample answer:** By creating a program that iterates through each element in the list and then comparing it with a variable that holds the current largest number, the largest number can be found in a list.

**5. Write a program to reverse a string.**

This question helps an interviewer analyze how well the candidate is familiar with string manipulation and writing a program that takes string as input and outputs the reversed string.

**Sample answer: **Taking a string as input and using string manipulation techniques, such as iteration or slicing, will reverse the order of its characters. Finally, the reversed string can be displayed.

**6. ****Write a program to check if a string is a palindrome. **

By asking this question, interviewers are able to evaluate a candidate’s ability to work with strings and conditionals.

**Sample answer: **Compare the original string with its reversed version through string manipulation techniques. If both the strings are identical, the input string is a palindrome.

**7. Write a program to find the factorial of a number.**

Interviewers can gauge the interviewee’s understanding of loops and basic mathematical operations.

**Sample answer: **Take a number as input and use a loop to calculate the factorial by multiplying each number from 1 to the given number.

**8. ****Write a program to check if a number is prime. **

This question helps hiring managers assess the candidate’s knowledge of loops and conditionals and their ability to write a program and using an appropriate algorithm.

**Sample answer: **Take a number as input and check if it can be divisible by any number from 2 to the square root of the number. If a divisor is found, it is not a prime number

**9. Write a program to find the Fibonacci series up to a given number.**

Interviewers can analyze the person’s grasp on series generation and loops and if they can apply it to real-world scenarios.

**Sample answer: **Use a loop to generate the Fibonacci series by adding the previous two numbers. This loop will continue until the generated number exceeds the given number.

**10. Write a program to convert Celsius to Fahrenheit.**

Hiring managers can evaluate how well the candidate is aware of basic mathematical operations since it involves the usage of appropriate formulas.

**Sample answer: **I would use the conversion formula: Fahrenheit = Celsius * 9/5 + 32, to calculate the equivalent temperature in Fahrenheit.

## Advanced Python coding interview questions

**1. Implement an LRU (Least Recently Used) Cache.**

Interviewers expect candidates to display their understanding of data structures and caching concepts along with their ability to design and implement an efficient data structure.

**Sample answer: **An LRU can be implemented by utilizing a combination of a dictionary and a doubly linked list to store the cached items. The dictionary provides fast access to the cache entries and the doubly linked list keeps the list of items based on recency.

**2. Given a list of numbers, find the maximum sum of a contiguous subarray.**

An interviewer is looking for the candidate’s problem-solving skills and understanding of algorithms along with how well they understand complex concepts.

**Sample answer: **The maximum sum of a contagious subarray in a list of numbers can be found by using the Kadane’s algorithm. I would iterate through the list while keeping track of the maximum sum found so far. If the sum is increased by the present element, it can be included, or a new subarray can be started.

**3. ****Implement a binary search tree and perform common operations such as insertion, deletion, and search. **

By asking this question, interviewers can assess the extent of a candidate’s knowledge of data structures along with their ability to implement fundamental operations. They are expected to explain the structure and characteristics of a binary search tree.

**Sample answer: **A binary search tree can be implemented by creating a Node class with left and right child pointers. These nodes can then be used to construct the binary tree and perform the given common operations.

**4. ****Write a function to check if a binary tree is balanced. **

The hiring manager will be expecting the candidate to demonstrate their understanding of binary trees and explaining their concepts and methods while also providing the function.

**Sample answer: **This can be done by calculating the height of the left and right subtrees. Then, by comparing the heights and ensuring that the difference is not more than 1, the binary tree can be balanced. This process has to be repeated for each node in the tree.

**5. ****Implement a stack using two queues. **

This question helps interviewer gauge how creatively a candidate can solve problems to provide a solution that maintains the stack’s behavior.

**Sample answer: **By using two deque objects from the collections module, a stack can be implemented using two queues. One queue for the main stack operations can be used and the other queue for temporary storage during push and pop operations.

**6. Given a string, find the longest substring without repeating characters.**

The interviewer is looking for the candidate’s grasp on string manipulation, problem solving skills, and explaining different approaches.

**Sample answer: **A sliding window approach can be used here. By maintaining a window that expands and contracts as a person iterates through the string and keeping track of the maximum length encountered without repeating characters, the longest substring can be found.

**7. Implement a Trie data structure and perform common operations such as insertion, deletion, and search.**

By asking this question, hiring managers can analyze how well the candidates have knowledge of performing key operations and showcasing knowledge of Trie traversal and manipulation.

**Sample answers: **After creating a Trie Node class with child pointers and a Boolean flag to indicate the end of a word, these nodes can be used to construct the Trie and perform common operations such as insertion, deletion, and search.

**8. ****Write a function to calculate the factorial of a number recursively. **

Interviewers assess the candidate’s knowledge of recursion and the ability to articulate a complex concept.

**Sample answer: **By writing a function that calls itself with a decremented input until it reaches the base case (1 or 0), the factorial of a number can be calculated recursively. Then, multiply each recursive call’s result by the current input value to calculate the factorial.

**9. ****Given a matrix, rotate it by 90 degrees in-place. **

The hiring managers are looking for the candidate’s ability to manipulate matrices and solve spatial transformation problems.

**Sample answer: **First, transpose the matrix and reverse each row or column depending on the desired rotation direction.

**10. Implement a depth-first search (DFS) algorithm to traverse a graph.**

This question helps interviewers understand the candidates’ knowledge of graph traversal algorithms and the ability to implement it while also explaining DFS.

**Sample answer: **This can be done by using a stack or a recursion to traverse a graph. Start from a certain node and visit its adjacent unvisited nodes. Repeat this process until all nodes are visited to maintain a visited set to avoid revisiting.

## Tips to prepare for Python interviews

**Master data structures, algorithms, and fundamentals**

Practice various data structures such as dictionaries, lists, stacks, queues, and trees. Some common algorithms include sorting, searching, and graph traversal. Additionally, don’t forget to master fundamentals of core Python concepts.

**Solve coding problems**

Any Python coding interview will require the candidate to solve coding problems. Practice this on different platforms such as Codewars, HackerRank, etc.

**Be prepared for common interview topics**

Some common interview topics are – recursion, dynamic programming, graph algorithms, system design, and so on. It’s also important to stay updated on the latest news and trends.

**Practice whiteboarding**

Practice solving Python coding problems with a pen and a paper or on a whiteboard. This helps in developing a structured thought process and practicing the interview environment. Consider pairing with a friend for programming. Explain to each other the thought process and concepts.

**Practice mock interviews **

Practicing mock interviews with friends or participating in coding practice sessions will help candidates immensely to prepare for Python interviews.

## Red Flags to Watch Out

**No understanding of Python basics**

A candidate displaying no understanding of Python fundamentals and is struggling to explain data types, control flow, and basic syntax. A weak foundation in Python can be a red flag.

**Lack of problem-solving skills**

No clear approach to solving coding problems. Lack of problem-solving skills can result in incorrect algorithms, which is a clear red flag.

**Poor communication skills**

Inability to explain the thought process and reasoning behind their solutions indicates poor communication skills. A candidate must be able to explain their code implementation and be able to collaborate in coding environments.

**Limited knowledge**

No knowledge of common Python libraries or frameworks relevant to the position. It’s also important to evaluate candidates based on their role and job description.

**Lack of attention to detail**

Inability to address error handling and exceptions in code shows that the candidate lacks attention to detail in their coding approach.

Python coding interviews can be nerve-wracking for many candidates, especially those who are new to the language and lack confidence in their skills. However, with proper preparation and practice, any worry can be removed. Candidates can also familiarize themselves with common Python concepts and slowly move up the level of difficulty. Engaging in coding exercises, participating in mock interviews, and improving communication skills can help prepare for Python interviews.