50+ Python Interview Questions To Secure A Job With

While Python has decreased in popularity over the past few years, it's still one of the most powerful programming languages. And is often asked about in interviews in order to understand a software engineers ability to be a polyglot. A polyglot is someone who understands multiple programming languages in order to choose the best tool for the job, often mixing multiple types of programming languages into one suite of solutions. When being asked Python interview questions its important to understand the pros and cons of the language itself. At the end of this article, I am providing some history on Python as well, which is helpful knowledge to ensure you have when going into an interview. All of the answers to these questions are completely mock, meaning they are correct, but you should still practice putting together your own answers from this study sheet. If you have any thoughts on how to improve these questions, please email me and I would be happy to answer them. You will experience these questions being asked of you as part of the technical interview process. You will also be asked about basic python scripting, coding and general developer related interview material.

1. What is Python? How well do you understand what it is?

Python is a highly interpreted, interactive and object-oriented scripting language. The language is designed to be highly readable as it frequently uses English keywords as opposed to punctuations and syntaxes. This means that Python experiences fewer syntactical constructions compared to other interpreted languages such as JavaScript and PHP.

2. What are some of the benefits of using Python programming?

• Python language can be typed dynamically. This means that you do not necessarily have to mention the data type of variables when they are being declared. Python also allows a set of variables such as var1=101 and var2 =” You are an engineer.” without an error.
• Python supports object-oriented programming where classes can be defined along with composition and inheritance. Python does not require access specifiers such as public or private.
• In Python, functions are like first-class objects which mean that they can be assigned to variables, be returned from other methods and pass as arguments. • Developing the Python language is quick. However, running the Python program is slower compared to other languages. Luckily, Python allows you to include the “C” language extensions in order to optimize your scripts.
• Python is used in several areas such as in web-based applications, big data analytics, data modeling and test automation among others. Alternatively, Python is also used as a “glue” layer to work with other languages.

3. What are some of the main differences between Python and Java?

Comparing Python vs. Java.
Comparison: Python vs. Java
Performance Speed: Python is Fast, Java is not as fast as Python
Indentation: Must be followed in Python, Java using proper flower braces is enough
Typing: In Python, dynamically typed, Java is static typed
Accessibility: In Python, simple and compact, Java not as much as Python
Platforms: In Python, not compatible to many, In Java platform independent
Database Access: In Python, weak compared to JAVA, Java is strong (JDBC)

4. How is static analysis performed in a Python application?

Static analysis can be performed using the PyChecer-a static analyzer that identifies a bug in a Python project and also establishes the complexity and style of related bugs. Another tool that can be used to perform static analysis in a python application is Pylint. Pylint checks whether the Python module used in a Python application satisfies the coding standards.

5. What is the function of a decorator used in a Python application?

A Python decorator is a relative change performed in Python syntax in order to adjust the functions more quickly.

6. How is memory management handled in a Python application?

• In a Python application, private heaps are used to maintain the memory. The heaps function by holding all Python objects and data structures. However, this area can only be accessed by a Python interpreter. Python programmers cannot use it.
• The private heaps that store memory are handled by the Python memory manager. The memory manager conducts the required allocation of the memory for python objects.
• In a Python application, there is also a built-in garbage collection system that salvages all the unused memory and offloads it to the heap space.

7. List down the main differences between lambda and def

• Lambda is a uni-expression function while def can hold multiple expressions. • Lambda forms a function object and returns it while def generates a function and designates a name to call it later.
• Lambda does not have return statements while def can have a return statement.
• Lambda can be used inside a list and dictionary.

8. What is a string in Python?

This is a sequence of alpha-numeric characters. A string can also be defined as an immutable object in Python. This means that strings cannot be modified once they are assigned to a value. There are several ways in Python that strings can be altered such as using join (), replace (), or split (). However, none of these methods can change the original object.

9. What is slicing in Python?

In a Python application, slicing is a string operation used to extract a part of the string or a list. For example, a string (say text) begins at index 0, and the nth character stores at position text [n-1]. Python can also perform what is referred to as reverse indexing (in the backward direction) with the help of negative numbers. The slice () in Python is a constructor function that generates a slice object. In the slice () method, there are three parameters that are allowed namely:

• Start – starting number for the slicing to begin.
• Stop – the number which indicates the end of slicing.
• Step – the value to increment after each index (default = 1)

10. What is %s in Python application?

Python supports the formatting of any possible value into a string. This means that it might contain some quite complex expressions. The %s format specifier’s role is to push values into a string. The formatting operation used in Python is also similar to the syntax C function printf () has.

11. In a Python application, is a string mutable or immutable?

Strings in a Python application are immutable.

For example, let’s say we have a “str” variable holding a string value. The container cannot be mutated i.e the string but, what the string contains that is the value and variable can be modified.

12. What is the index in Python?

An index in a Python application is an integer data-type that denotes a certain position within an ordered list or string.

Strings are also lists of characters in Python that can be accessed using the index that starts from zero and extends to the length minus one.

An example of indexing in a string program is:

Program: 0 1 2 3 4 5

13. How is Python interpreted?

Python is an integrated language based on the fact that Python programs run directly from the source code. Python converts the source code written by the programmer into an intermediate language. The intermediate language is again translated into machine language that is executable.

14. What is PEP 8?

PEP 8 is a set of recommendation or a coding convention regarding how Python code is written.

15. What is the role of PYTHONSTARTUP, PYTHONCASEOK, PYTHONHOME, PYTHONSTARTUP environment variables in a Python application?

• PYTHONSTARTUP: This variable contains the path of an initialization file that contains the Python source code. The PYTHONSTARTUP is executed every time the Python interpreter is started. In Unix, the variable is known as .pythonrc.py and contains commands that load utilities or modify the PYTHONPATH.
• PYTHONCASEOK: This is the variable used in Windows to instruct Python to find the first case-insensitive match in a statement.
• PYTHONHOME: This variable acts as an alternative module search path and is usually embedded in the PYTHONSTARTUP or PYTHONPATH directories in order to ease the process of switching modules easier.

15. What data-types does Python support?

• Numbers
• String
• List • Tuple • Dictionary

16. What are the main differences between list and tuples in a Python application?

Lists are mutable which means that they can be edited while tuples are immutable meaning that they cannot be edited.

Lists are slower than turples

The syntax for a list is list_1 = [10, ‘Chelsea’, 20] while the syntax for a turple is tup_1 = (10, ‘Chelsea’, 20).

17. Explain inheritance in Python

Inheritance in a Python application allows one class to gain all the attributes and methods of another class. Inheritance also ensures that codes can be reused as well as making it easier to create and maintain an application. There are different types of inheritance in Python namely;

• Single inheritance: In single inheritance, the derived class acquires all members of a single superclass.
• Multi-level inheritance: In multi-level inheritance, a derived class d1 is inherited from base class base1 while d2 is inherited from base 2.
• Hierarchal inheritance: this is where any number of child classes can be inherited from a single base class.
• Multiple inheritances: This is a derived class that is inherited from more than a single base class.

18. Why isn’t all the memory De-allocated whenever Python exits?

Whenever Python exists, objects that are not referenced from the global namespaces are not always freed or de-allocated-especially the modules that are with circular references.

Because of its in-built clean-up mechanism, Python will try to de-allocate or destroy every other object.

19. What is a dictionary in Python?

A dictionary in Python refers to the built-in data-types. The term refers to the one-on-one relationship between values and keys. Dictionaries contain key pairs and their corresponding values.

20. What built-in types are provided by Python?

There are two built-in types in a python application namely; mutable and immutable types. Mutable built-in types contain lists, sets, and dictionaries while immutable built-in types contain strings, tuples, and numbers.

21. Mention the main benefits of using Python

• Python has a huge standard library compatible with most internet applications such as Email, HTML, and HTTP.
• Python does not require an explicit memory management system as the interpreter automatically allocates the memory to new memory and frees them during the clean-up. • Python is easy to read because of the use of brackets in the program.
• Ease-of-usability for beginners
• Python has built-in data-types that save programming time and effort used in declaring variables.

22. What is a Flask in Python and what are its benefits?

Flask is part of a micro-framework that has little or no dependencies on external libraries. This feature is what makes the framework lightweight in nature as there is little dependency to update.

23. Mention the differences between Flask, Pyramid, and Django

• Flask is a micro-framework found in Python that is primarily built for smaller applications with simpler requirements. Flask requires the users to use an external library.
• Pyramids, on the other hand, are built for large applications. They provide flexibility and lets developers use the correct tools for web-based projects. Using Pyramid, a developer can choose the URL structure, database, templating style and many more.
• Django operates in the same manner that a Pyramid does but, in this case, Django includes an ORM.

24. In Python, what is Flask-WTF and what are some of its features?

Flask-WTF helps to integrate WTForms. Some of the main features of Flask-WTF are;

• Integration with wtforms
• Secure form with csrf token
• Global csrf protection
• Internationalization integration
• Recaptcha supporting
• File upload that works with Flask Uploads

25. What are the two main ways that the Flask scripts work?

• By being the import path of your application
• By being the path to a Python file

26. Explain how the database is connected in a Python Flask

Flask supports RDBS which are database-powered applications. These systems require the creation and piping of a schema.file into a sqlite3 command. This means that a sqlite3 command must be installed for the database to be initiated in the Flask.

Flask in a Python application allows requests to the database in the following ways;

• before_request (): called before a request and pass no arguments
• after_request (): called after a request and pass the response that is sent to the client
• teardown_request (): called in situations when an exception is raised, and the response is not guaranteed. They are called after the response has been constructed. They are not allowed to modify the request, and their values are ignored.

27. Assuming that you have multiple Memcache servers running your Python application, and one of the memcacher server fails while still containing some data, will there be any attempt from your Python application to get key data from the failed server?

The data contained in the failed server will not be removed. However, there is a provision for auto-failure where you can configure for multiple nodes.

28. How can you minimize the Memcached server outages in your Python development?

• When one instance fails in a Python development, several of them also go down. This ultimately increases the load on your database server since the lost data will be reloaded every time the client makes a request. In order to avoid such a situation, your code should be written to minimize cache stampedes which then leave little or no impact. • Another method of minimizing Memcached server outages is by bringing up an instance of Memcached on a new machine while using the lost machine’s IP address.
• Server outages can also be minimized through the use of codes. Code gives you the freedom to change the Memcached server list with minimal work.
• Some Memcached clients also set the timeout value in order to reduce the possibility of server outages. This means that when the Memcached server goes down, the client will keep on trying to send multiple requests until the time-out limit is reached.

29. What is Dogpile effect in a Python development and how can it be prevented?

Dogpile effect refers to the situation where the cache expires and the website is hit by several requests from the client at the same time. This effect, however, can be prevented using the semaphore lock. When using the semaphore lock, when the values expire, the process is locked and the system begins generating new values.

30. How should Memcached not be used in a Python project?

• One of the most common misuses of Memcached is that it is used to store data as opposed to being used as a cache.
• Memcached should never be used as the only source of information that is used to run your application. Data should also be made available through a different source as well.
• Memcached should never be used to perform a query over the data or iterate over the contents to extract information as it is just a key or value and therefore not designed to perform the two actions.
• Memcached has no security features either in the form of authentication or encryption.

31. Give a brief description of all the operators that Python has

Python has a total of five types of operators. These operators are;

• Arithmetic operators: These operators are used for arithmetic operations.
• Comparison operators: These operators are used to make a comparison between two variables with the same data-type.
• Bitwise operators: These operators are used to perform bitwise operations between variables.
• Logical operators: These operators are used to perform logical AND, OR, NOT between different expressions.
• Python Assignment Operators: These operators perform both arithmetic and assignment operations.

32. What are the main advantages of Python Recursions?

Using Python recursion requires less effort as the code written using Python recursion is relatively smaller than the code being implemented by the loops. In addition to this, a code written by Python recursion is easy to understand.

33. What are some of the disadvantages of using Python recursion?

The downside of using Python recursion is that it requires more function call. The higher the number of function calls required by a code, the greater the memory that code consumes. This means that using Python recursion can at times cause a memory overflow. If your code is not very efficient, the time taken to call a function is even longer. Once the task function is completed, the time taken to re-execute the parent function from the previous state is also longer. In simple terms, Python recursion consumes more time to perform its task.

34. How do you use GUI to test your code in Python?

GUI is an editor or rather a graphical version of the interactive shell. It is possible to write or load code but there is no automatic testing.

35. What are some of the activities that Python is best at?

Python is a general-purpose scripting language that is applicable to different classes of problems. Python comes with a large standard library that covers among other areas; string processing, regular expressions, calculating the difference between files, internet protocols such as HTTP, POP, SMTP, FTP, IMAP, XML-RPC and CGI programming, software engineering applications such as unit testing, parsing python code and profiling; operating system interfaces such as file systems, systems calls and TCP/IP sockets.

36. Explain how the Python version numbering scheme work

Ideally, python versions are either numbered A.B or A.B.C

• A is described as the major version number that is only incremented to address major changes in the language. • B is the minor version number that is incremented for less-major changes.
• C is the micro-level version number that is incremented for each bug fix release.
It is important to note that not all releases are bug-fix releases. In the run-up to a major release, ‘A’ series of development are created and denoted as alpha, beta or release candidates.

Alphas are early releases whereby the interfaces haven’t been finalized yet. It is however not unexpected to see a change in the interface between two alpha releases. Beta releases are more stable and preserve the existing interfaces. In addition, beta releases also add new modules but at the same time ensure that the release candidates are frozen. Once frozen, the release candidates cannot make any changes except when needed in order to fix critical bugs.

• Alpha, beta and release candidates all have an additional suffix.
• The suffix for an alpha version is “aN” for some small number N,
• The suffix for a beta version is “bN” for some small number N,
• The suffix for a release candidate version is “cN” for some small number N.

37. How does a user send mail when using a Python Script?

A mail can be sent using the standard library module smtplib in python. Below is a simple interactive example that works on any host and is supported by an SMTP listener.

import sys, smtplib
fromaddr = raw_input(“From: “)
toaddrs = raw_input(“To: “).split(‘,’)
print “Enter message, end with ^D:”
msg = ”
while 1:
line = sys.stdin.readline()
if not line:
break
msg = msg + line
# the actual mail send
Server = smtplib.SMTP(‘localhost’)
server.sendmail(fromaddr, toaddrs, msg)
server.quit ()

39. When using a Python application, how do you make a thread work when none of the threads are working?

Immediately after the main thread exits, all threads are killed in a Python application. Ideally, this means that the main thread is working too quickly giving the rest of the threads no time to do any work. A simple method to fix this issue is by adding a sleep at the end of the program that is long enough for all the threads to complete.

Example:
import threading, time
def thread_task(name, n):
for i in range(n): print name, i
for i in range(10)

40. What are Tuple objects in Python?

Tuple objects are created by either calling the tuple function or by assigning multiple values to a single variable. They can also be created by using parenthesis. Tuple objects are immutable objects where both duplicate and heterogeneous elements are allowed. Tuple also supports both positive and negative indexing. The elements found in Tuple can either be mutable or immutable.

41. What are some of the key features of the Dictionary in a Python setup?

• Dictionary objects are created using curly brackets {} or by calling the dictionary function.
• Objects in the dictionary are mutable
• Dictionary represents a key value base
• Each of the key-value pairs in a Dictionary is known as an item.
• Keys in a dictionary must be immutable.
• In a Dictionary, values can be duplicated but duplicate keys are not allowed.
• Insertion order is not preserved.
• Dictionary allows both heterogeneous keys and values.

42. What are packages in Python?

A package in Python is nothing else but a dictionary or folder that represents a collection of modules. A package can also contain sub-packages. In a Python application;

• It is possible to import the modules of the package by using package name.module name
• It is also possible to import the modules of the package by using package name.subpackage name.module name

43. What is file handling in Python?

• A file in python can be described as the location within a disc where data is stored in a permanent manner.
• Python as a scripting language has several functions and methods that provide communication between Python programs and other files.
• Python programs can open, read and close the file whenever necessary. The opening of files in a Python application is done by calling open functions of built-in modules. When opening a file, the users have to specify the mode of the file. The mode of the file indicates the purpose for which the purpose is going to be used for once opened.

44. What are Runtime Errors in a Python setup?

Runtime errors occur once the execution of programs is started. Runtime errors often occur because of the following reasons.

• Invalid Input
• Invalid Logic
• Memory issues
• Hardware failures and so on

45. What is Abnormal Termination is a Python configuration

Just as the name suggests, abnormal termination refers to the act of terminating programs while it is in the middle of its execution and the last statement of the main module has not been executed yet. In programming languages, an abnormal termination is an undesirable situation that could cause minor internal malfunctions.

46. What are the main differences between Methods and Constructors in Python?

• Methods are executed whenever they are called whereas Constructors are executed automatically whenever the object is created.
• One method can be called for ‘n’ members of lines whereas one constructor can only be executed once.
• Methods are used to represent business logic when performing their operations while constructors are used to define and initialize the non-static variable.

47. What is Garbage Collection in Python?

Garbage collection refers to the concept of removing unused and unreferenced objects from the memory collection. Some of the key features of the concept include;

• Once garbage collection is executed, more space is made available for both the program and the execution of other programs become faster.
• The garbage collector is a predefined program that removes unused and unreferenced objects in a Python framework.
• Unused or unreferenced objects are those count is zero.
• The numbers of reference variables pointing to a specific object are also known as the reference count of the object.
• In simple terms, the garbage collection process begins during the execution of a python program. If any of the objects reference counts is zero, the Python interpreter calls the garbage collector to remove the object from the memory location.

48. What are DML commands used for in Python programs?

• DML commands are commands used to modify data in database objects.
• Whenever the DML commands are executed, the records are modified temporarily.
• Whenever the roll-back command is run, the modified records are supposed to go back to their original state.
• In order to permanently modify the records of a database, the “commit” command is used.
• After the execution of the commit command even after the rollback command has been executed, the modified records will not return to their original state.
• When the DML commands are run through a Python program, the number of records that will be modified as a result of that command is stored into the row count attribute of the cursor object.

9. What Are Applications of Python?

Applications of Python
Applications of Python and JAVA.NET
Automation App: PYTHON (NO) JAVA.NET (NO)
Data Analytics: PYTHON (NO) JAVA.NET (NO)
Scientific App: PYTHON (NO) JAVA.NET (NO)
Web App: PYTHON (YES) JAVA.NET (YES)
Web Scrapping: PYTHON (NO) JAVA.NET (NO)
Test Cases: PYTHON (YES) JAVA.NET (YES)
Network with JOT: PYTHON (YES) JAVA.NET (NO)
Admin Script: PYTHON (NO) JAVA.NET (NO)
GUI: PYTHON (YES) JAVA.NET (YES)
Gaming: PYTHON (YES) JAVA.NET (YES)
Animation: PYTHON (NO) JAVA.NET (NO)

50. What is multithreading in a Python program?

Multithreading is logic or functionality in Python that can execute simultaneously along with other programs. Some of the key features of multithreading include;

• Multithreading is a relatively lightweight process
• Any program that is being executed during multithreading is referred to as a process.
• Threads in Python can be defined by overwriting run method or the thread class.
• The thread class refers to a predefined class that is defined in a threading module.
• The thread module is a predefined module.

51. What is NumPy and how is it better than the list in Python?

NumPy is a Python package that is used for scientific computing and deals with larger data sizes. NumPy has a powerful N-dimensional array object as well as a set of advanced functions. This means that it is better than the inbuilt list in Python because of the following reasons;

• NumPy arrays are more compact than lists.
• Reading and writing items is faster with NumPy.
• Using NumPy is more convenient than using the standard list.
• NumPy arrays are more efficient as they augment the functionality of lists in Python.

Core benefits of using python

When a future employer asks you why you might use python versus another programming language, your answer should be its ability to be very focused on a single task and be incredibly lightweight. Python is often used in quantitative trading systems because it has the ability to execute its logic extremely quickly. Its entire package is also extremely lightweight, meaning it can be moved and executed between servers and locations quite easily. This is one of the main advantages to the programming language compared to others. It is still widely used by those looking to develop applications for the web, but its losing popularity to other languages that have more opensource software available.

author: patrick algrim
About the author

Patrick Algrim is an experienced executive who has spent a number of years in Silicon Valley hiring and coaching some of the world’s most valuable technology teams.

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