50 Top Python Interview Questions You Should Know in 2021

50 Top Python Interview Questions You Should Know in 2021

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Any list of best programming languages you choose for 2021, one name will always occupy a prominent position: Python. Most of the great organizations around the world use Python in some form. NASA, Google, Netflix, Spotify, and countless more all use the language to help power their services. It is the third most popular programming language in the world, after Java and C.

Thus, if you want to know whether learning Python can help you achieve a productive life, the answer is Yes. But before that, you would have to learn Python interview questions to increase your success rate.

Topics we will be covering in this article are:

  • Why should you learn Python?
  • Uses of Python
  • Python Interview Questions & Answers

Why Should You Learn Python?

We know why Python is so popular right now, but why should you learn how to use it? Well, the answer is simple. Apart from its ease of use and versatility, Python has several other advantages:

  • Demand for Python Developers: There is a huge demand for developers who have excellent Python skills. If you wish to start or change careers, it's a vital skill to have.
  • Well-Paid Career: According to data from the UK, Python programmers earn an average salary of about $65,000. So, it is without a doubt a profitable career for you.
  • Job Opportunities: Python can be used in many emerging technologies, like AI, machine learning, and data analytics, making it a future-proof skill. The skills you gain now will come in handy throughout your career.

Uses Of Python

Learning Python is a popular and in-demand skill. But, where does Python programming come in handy? Here is a list of places where you can use Python:

  • AI and Machine Learning
  • Data Visualisation
  • Programming Applications
  • Data Analytics
  • Game Development
  • Web Development
  • Finance
  • Language Development
  • Design
  • SEO

Python Interview Questions and Answers

First, we will start with questions related to beginners, and then we will move on to advanced questions.

Python Interview Questions For Beginners

1) What is Python?

Python is an object-oriented (based around data), high-level (simpler for humans to understand) programming language. It was introduced in 1992 and is relatively intuitive to write and understand. Therefore, it is an ideal coding language for those who want to develop quickly.

2) What are the benefits of using Python?

The diverse applications of the Python language are due to the combination of features that makes this language superior to others. There are many advantages to programming in Python, including:

  • Open-Source and Community Development
  • Learning Ease and Support Available
  • User-Friendly Data Structures
  • Presence Of Third-Party Modules
  • Productivity And Speed
  • Extensive Support Libraries

3) What are Tuples in Python?

A tuple is a sequence data type in Python, which holds multiple items in a single variable. It is one of four built-in Python data types used for storing data collections.

4) What is the difference between Tuples and List?

Tuples:

  • Tuples are similar to a list but are placed within parenthesis.
  • The element and size are changeable.
  • Tuples cannot be updated.
  • Tuples act as read-only lists.
  • They are surrounded by ( )
  • Tuple Code Example: tup = (1, "a", "string", 1+2)

Lists:

  • Lists are used to create a sequence.
  • The element and size are not changeable.
  • Lists can be updated.
  • Lists act as a changeable list.
  • They are surrounded by [ ]
  • Lists Code Example: L = [1, "a" , "string" , 1+2]

5) What are the Positive and Negative indices?

Positive indexing in Python is accomplished by passing a positive index into square brackets. The index number starts from 0, which means the first character of a string. For example:

my_str = "Python Guides" print(my_str[0])

Negative indexing in Python involves passing a negative index, which we want to access within square brackets. Here, the index number begins with -1, which represents the last character of a string. For example:

my_str = "Python Guides" print(my_str[-1])

6) What are the limitations of Python?

Python has the following limitations:

  • Design restrictions.
  • It is slower in comparison to C and C++ or Java.
  • It is ineffective in mobile computing.
  • The database access layer is underdeveloped.

7) Can we reverse a list in Python?

Yes, we can reserve a list using the reverse() method. Here is a representation of the code.

def reverse(s): 
  str = "" 
  for i in s: 
    str = i + str
  return str

8) How many ways are there to apply reverse string?

There are five ways in which you can apply a reverse string:

  • Loop
  • Reversed
  • Stack
  • Recursion
  • Extended Slice Syntax

9) Why do we need a break in Python?

In Python, the break command helps control the loop by breaking the current loop from execution and transferring control to the next block.

10) Do run-time errors exist in Python? Give an example?

Yes, run-time errors do exist in Python. It happens when Python understands what you are saying but runs into trouble following your instructions. For example:

Please eat the Table

The sentence looks grammatically correct and makes sense. But once you start eating a table, then you will start causing problems for yourself. This is called a run-time error because it occurs after the program starts running.

11) What are Python modules? Name some Python modules that are frequently used?

A Python module is a file that contains Python code. The code can either be a function, class, or variable. Python modules are .py files containing executable code. These are some of the commonly used built-in modules:

  • os
  • sys
  • math
  • random
  • data time
  • JSON

12) How to install Python on Windows and set path variables?

To install Python on Windows, follow these simple steps:

  • Install python from this link.
  • After installation, look for the directory where you have installed python using the following command on your command prompt: cmd python.
  • Then move on to advanced system settings and add a new variable and name it as PYTHON_NAME and paste the copied path.
  • Look for the path variable, select its value and select ‘edit’.
  • Add a semicolon towards the end of the value if it’s not present and then type %PYTHON_HOME%

13) What are local variables and global variables in Python?

Local Variables: Any variable declared inside a function is known as a local variable. Unlike global variables, this variable exists in the local space.

Global Variables: Any variables declared outside a function or global area are called global variables. These variables can be accessed by any function in the program.

14) What is the difference between Python Arrays and lists?

In Python, both arrays and lists store data in the same way. However, arrays can hold only a single type of element whereas lists can hold any data type elements.

15) Is indentation required in python?

Indentation is vital to Python since it specifies blocks of code. All code within classes, functions, loops, etc is specified within an indented block. It is usually done using four spaces. The code will not execute properly if it is not indented, and it will also be prone to error.

16) What is init ?

init is a method or constructor in Python. It is automatically called to allocate memory when a new object or instance is created. init is present in all classes.

17) What are functions in Python?

A function is a block of code that executes only when it is called. The def keyword is used to define a Python function.

18) How do you write comments in python?

Normally, Comments in Python language start with a # character. But, alternatively, at times, commenting is performed using docstrings (strings surrounded by triple quotes). Example:

#Comments in Python start like this

print("Comments in Python start with a #")

19) How will you capitalize the first letter of string?

By using capitalize() method, we can capitalize the first letter of a string in Python. Also, if the string already contains a capital letter, it returns the original string.

20) What is Pickling and Unpickling?

The pickle module converts any Python object into a string representation and dumps it into a file by using the dump function, this process is referred to as pickling. While unpickling refers to the process of retrieving the original Python objects from the stored string representations.

21) What are docstrings in Python?

Docstrings aren't necessarily comments, but rather documentation strings. The docstrings are enclosed in triple quotes. Since they are not assigned to a variable, they can sometimes be used as comments as well.

22) What is the usage of help() and dir() function in Python?

The help() and dir() functions are both available from the Python interpreter and provide access to a list of all the built-in functions.

  • Help() function: The help() function is used to display the documentation string and also facilitates you to see the help related to modules, keywords, attributes, etc.

  • Dir() function: The dir() function is used to display the defined symbols.

23) What is the purpose of is, not and in operators?

Operators are special functions that take one or more values and produce a corresponding result.

is: returns true when 2 operands are true (Example: “a” is ‘a’)

not: returns the inverse of the boolean value

in: checks if some element is present in some sequence

24) What does len() do?

It determines the length of a string, list, array, etc. Example:

1 stg='ABCD'

2 len(stg)

25) What are args and Kwargs in Python? And why we use it?

We use args when we are unsure about how many arguments are going to be passed to a function, or whether we want to pass a stored list or tuple of arguments to a function.

kwargs is used when we do not know how many keyword arguments will be passed to a function or when we want to pass the values of a dictionary as keyword arguments. The identifiers args and kwargs are a convention, you could also use bob and *billy, but that would not be advisable.

Python Interview Questions For Professionals

26) How will you differentiate between NumPy and SciPy?

Usually, NumPy contains the array data type and basic operations, such as basic element-wise functions, indexing, reshaping, and sorting. Moreover, all the numerical code exists in SciPy.

To maintain compatibility, NumPy tries to retain all features supported by either of its predecessors. Therefore, NumPy contains a few linear algebra functions despite these functions being more suitably found in SciPy.

SciPy includes the linear algebra modules available in NumPy, as well as several other numerical algorithms.

27) What is a Dictionary in Python? Explain using an example.

Dictionary in Python is an unordered collection of data values such as a map. It represents a one-to-one relationship between keys and values. A usual Dictionary contains pair of keys and their corresponding values, indexed by keys.

Let us take an example with three keys, namely Website, Language, and Offering. Their corresponding values are coursesity. com, Python, and Tutorials. The code, for instance, will be:

dict={‘Website’:‘coursesity.com’, ‘Language’:‘Python’:‘Offering’:‘Tutorials’}
print dict[Website] #Prints coursesity.com
print dict[Language] #Prints Python
print dict[Offering] #Prints Tutorials

28) Explain split(), sub(), subn() methods of “re” module in Python.

Python's "re" module provides three methods for modifying strings. They are:

  • split() – uses a regex pattern to split a given string into a list.
  • sub() – locates any substring that matches the regex pattern and replaces it with an alternative string.
  • subn() – returns a new string including the number of replacements, similar to sub().

29) Python does not deallocate memory when it exits. Why is it so?

Whenever Python exits, its built-in cleanup mechanism tries to deallocate or destroy all other objects. However, Python modules with circular references to other objects or objects referenced from the global namespaces aren't always deallocated or destroyed.

There is no way to deallocate the memory reserved by the C library.

30) Observe the following code:

A0 = dict(zip(('a','b','c','d','e'),(1,2,3,4,5)))
A1 = range(10)A2 = sorted([i for i in A1 if i in A0])
A3 = sorted([A0[s] for s in A0])
A4 = [i for i in A1 if i in A3]
A5 = 
A6 = [[i,i*i] for i in A1]
print(A0,A1,A2,A3,A4,A5,A6)

Write down the output of the code.

A0 = {'a': 1, 'c': 3, 'b': 2, 'e': 5, 'd': 4} # the order may vary

A1 = range(0, 10)

A2 = []

A3 = [1, 2, 3, 4, 5]

A4 = [1, 2, 3, 4, 5]

A5 =

A6 = [[0, 0], [1, 1], [2, 4], [3, 9], [4, 16], [5, 25], [6, 36], [7, 49], [8, 64], [9, 81]]

31) What is Flask and what are its benefits?

Flask is a Python web microframework that depends on Jinja2 and Werkzeug. Therefore, it has some notable advantages:

  • Flask is not dependent on external libraries.
  • The web microframework is lightweight because there is a bit of external dependency to update and fewer security bugs.
  • It features an inbuilt development server and a fast debugger.

32) What are Negative Indexes. Why are they used?

Python sequences are indexed. It contains both positive and negative numbers. Positive numbers have 0 as the first index, one as the second index, etc. Thus, any index for a positive number n is n-1. Negative numbers, unlike positive numbers, are indexed from -1, which represents the last index in the sequence.

Similarly, -2 illustrates the penultimate index. In this case, the index is negative. A negative index is used for:

  • Taking out any new-line spaces from the string, thus allowing the string to accept the end character, represented as S[:-1]
  • Displaying the index to representing the string in the correct order

33) What do you mean by compilation and linking in Python?

Compiling and linking are required processes in Python for ensuring that new extensions are compiled without erroneous results. Linking initiates when the compilation is complete.

In dynamic loading, the compilation and linking process depends on the style provided by the concerned system. To provide dynamic loading of the configuration setup files and rebuild the interpreter, the Python interpreter is used.

34) Explain memory management in Python?

Python private heap space takes the place of memory management in Python. It contains all data structures and Python objects. The interpreter is chargeable for taking care of this non-public heap, and therefore the computer programmer doesn't have access to it. The Python memory manager is chargeable for the allocation of the Python heap house for Python objects.

The programmer might access some tools for the code with the assistance of the core API. Additionally, Python provides an inbuilt garbage collector, which recycles all unused memory, frees the memory, and makes it available to heap space.

35) What is the Lambda function?

An anonymous function is known as a lambda function. This function can have only one statement but can have any number of parameters.

a = lambda x,y : x+y
print(a(5, 6))

36) How to remove values to a python array?

You can remove array elements by using the pop() or remove() method. The difference between these two functions is that the former returns the deleted value while the latter does not. Example:

1. a=arr.array('d', [1.1, 2.2, 3.8, 3.1, 3.7, 1.2, 4.6])
2. print(a.pop())
3. print(a.pop(3))
4. a.remove(1.1)
5. print(a)

Output:

4.6

3.1

array(‘d’, [2.2, 3.8, 3.7, 1.2])

37) How is Multithreading achieved in Python?

  1. Python has a multi-threading package, but if you want to multi-thread to speed up your code, then it's usually not a good idea to use it.

  2. In Python, there is a construct called GIL (Global Interpreter Lock). GILs ensure that only one of your 'threads' can execute at a time. Threads acquire GILs, do a little work, and then send GILs on to the next thread.

  3. To the human eye, this may look a lot like parallel processing, but it is actually just taking turns using the same CPU core.

  4. All this GIL passing adds overhead to execution. Thus, if you want to make your code run faster, you shouldn't use the threading package.

38) What are Python libraries? Name a few of them.

Python libraries are collections of Python packages. Some of the commonly used python libraries are – Numpy, Pandas, Matplotlib, Scikit-learn, and many more.

39) How are classes created in Python?

Class in Python is created using the class keyword. Example:

  1. class Employee:
  2. def init(self, name):
  3. self . name = name
  4. E1=Employee("abc")
  5. print(E1 . name)

40) What is Polymorphism in Python?

Polymorphism is the ability to take on multiple forms. Therefore, if the parent class has a method named ABC, then the child class can also have a method with the same name with its parameters and variables. Polymorphism is possible in Python.

41) Define encapsulation in Python?

Encapsulation is the process of binding the code and the data together. A Python class is an example of encapsulation.

42) How do you do data abstraction in Python?

Data Abstraction hides the implementation and provides only the details required for a given purpose. Python supports this by using interfaces and abstract classes.

43) Does python make use of access specifiers?

Python does not deny access to instance variables or functions. It describes the practice of prefixing names of variables, functions, or methods with a single or double underscore to imitate private and protected access specifiers.

44) Is Django better than Flask?

Django and Flask map the URLs or addresses typed into the web browsers to Python functions.

In comparison to Django, Flask is simpler, however, Flask does not do a lot for you, meaning you will have to specify the details, whereas Django does much for you so you do not have to do much work.

Django utilizes prewritten code, which the user must analyze, whereas Flask allows the users to write their own code, making it easier to understand. Both are technically good, and both have their pros and cons.

45) Mention what the Django templates consist of.

The template is a simple text file that can create any text-based format like XML, CSV, HTML, etc. In a template, variables are replaced with values when the template is evaluated, and tags (%tag %) control the logic.

46) What is a map function in Python?

The map function executes the function given as the first argument on all the elements of the iterable given as the second argument. Whenever a function takes more than 1 argument, then many iterables are presented.

47) How do you make 3D plots/visualizations using NumPy/SciPy?

NumPy and SciPy are not capable of 3D graphics, but there are packages available that integrate with NumPy in the same way as 2D plotting. Matplotlib provides basic 3D plotting in the mplot3d package, whereas Mayavi offers an extensive range of 3D visualization capabilities, using the powerful VTK engine.

48)Explain what Flask is and its benefits?

Flask is a Python web microframework based on Werkzeug, Jinja2, and good intentions under the BSD license. Their dependencies include Werkzeug and Jinja2. This means it will have little to no dependencies on external libraries. While it makes the framework light, it is less dependent on updates and less prone to security vulnerabilities.

It is possible to remember information between each request in a session. In a flask session, a signed cookie is used so that the user may see and modify the session contents. The users can modify the session if only they have the secret key Flask.secret_key.

49) Does Python have OOps concepts?

Python is an object-oriented programming language. Meaning, Python can solve any program by creating an object model. Nevertheless, Python can be viewed as both a procedural and structural language.

50) Mention the differences between Django, Pyramid, and Flask.

  • Flask is a "microframework" mainly designed for small applications with simpler requirements. Flask requires external libraries. It is ready to use.
  • Pyramid is designed for larger applications. This gives developers flexibility and lets them choose the right tools for their projects. It is up to the developer to set the database, URL structure, and Templating style. The Pyramid is highly configurable.
  • Like Pyramid, Django can also be used for larger applications. It includes an ORM.

If you have made it this far, then certainly you are willing to learn more. Here are some more topics related to interviewing questions that we think will be interesting for you.

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