Data Science with Python Interview Questions and Answers

Data Science with Python Interview Questions and Answers

Last updated on 24th Oct 2020, Blog, Interview Question

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In that spirit, here are my python interview/job preparation questions and answers. Most data scientists write a lot of code so this applies to both scientists and engineers.Whether you’re interviewing candidates, preparing to apply to jobs or just brushing up on Python, I think this list will be invaluable.

1. What is Python? What are the benefits of using Python?


Python is a programming language with objects, modules, threads, exceptions and automatic memory management. The benefits of pythons are that it is simple and easy, portable, extensible, build-in data structure and it is an open source.

2. What is PEP 8?


PEP 8 is a coding convention, a set of recommendation, about how to write your Python code more readable.

3. What is pickling and unpickling?


Pickle module accepts any Python object and converts it into a string representation and dumps it into a file by using dump function, this process is called pickling. While the process of retrieving original Python objects from the stored string representation is called unpickling.

4. How Python is interpreted?


Python language is an interpreted language. Python program runs directly from the source code. It converts the source code that is written by the programmer into an intermediate language, which is again translated into machine language that has to be executed.

5. How memory is managed in Python?


Python memory is managed by Python private heap space. All Python objects and data structures are located in a private heap. The programmer does not have an access to this private heap and interpreter takes care of this Python private heap.

The allocation of Python heap space for Python objects is done by Python memory manager. The core API gives access to some tools for the programmer to code.

Python also have an inbuilt garbage collector, which recycle all the unused memory and frees the memory and makes it available to the heap space.

6. What are the tools that help to find bugs or perform static analysis?


PyChecker is a static analysis tool that detects the bugs in Python source code and warns about the style and complexity of the bug. Pylint is another tool that verifies whether the module meets the coding standard.

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7. What are Python decorators?


A Python decorator is a specific change that we make in Python syntax to alter functions easily.

8. What is the difference between list and tuple?


The difference between list and tuple is that list is mutable while tuple is not. Tuple can be hashed for e.g as a key for dictionaries.

9. How are arguments passed by value or by reference?


Everything in Python is an object and all variables hold references to the objects. The references values are according to the functions; as a result you cannot change the value of the references. However, you can change the objects if it is mutable.

10. What is Dict and List comprehensions are?


They are syntax constructions to ease the creation of a Dictionary or List based on existing iterable.

11. What are the built-in type does python provides?


There are mutable and Immutable types of Pythons built in types Mutable built-in types

  • List Sets
  • Dictionaries Immutable built-in types
  • Strings Tuples Numbers

12. What is namespace in Python?


In Python, every name introduced has a place where it lives and can be hooked for. This is known as namespace. It is like a box where a variable name is mapped to the object placed. Whenever the variable is searched out, this box will be searched, to get corresponding object.

13. What is lambda in Python?


It is a single expression anonymous function often used as In-line function.

14. Why lambda forms in python does not have statements?


A lambda form in python does not have statements as it is used to make new function object and then return them at runtime.

15. What is pass in Python?

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Pass means, no-operation Python statement, or in other words it is a place holder in compound statement, where there should be a blank left and nothing has to be written there.

16. In Python what are iterators?


In Python, iterators are used to iterate a group of elements, containers like list.

17. What is unit test in Python?


A unit testing framework in Python is known as unittest. It supports sharing of setups, automation testing, shutdown code for tests, aggregation of tests into collections etc.

18. In Python what is slicing?


A mechanism to select a range of items from sequence types like list, tuple, strings etc. is known as slicing.

19. What are generators in Python?


The way of implementing iterators are known as generators. It is a normal function except that it yields expression in the function.

20. What is docstring in Python?


A Python documentation string is known as docstring, it is a way of documenting Python functions, modules and classes.

21. How can you copy an object in Python?


To copy an object in Python, you can try copy.copy () or copy.deepcopy() for the general case. You cannot copy all objects but most of them.

22. What is negative index in Python?


Python sequences can be index in positive and negative numbers. For positive index, 0 is the first index, 1 is the second index and so forth. For negative index, (-1) is the last index and (-2) is the second last index and so forth.

23. How you can convert a number to a string?


In order to convert a number into a string, use the inbuilt function str(). If you want a octal or hexadecimal representation, use the inbuilt function oct() or hex().

24. What is the difference between Xrange and range?


Xrange returns the xrange object while range returns the list, and uses the same memory and no matter what the range size is.

25. What is module and package in Python?


In Python, module is the way to structure program. Each Python program file is a module, which imports other modules like objects and attributes.

The folder of Python program is a package of modules. A package can have modules or subfolders.

26. Mention what are the rules for local and global variables in Python?


1.Local variables: If a variable is assigned a new value anywhere within the function’s body, it’s assumed to be local.

2.Global variables: Those variables that are only referenced inside a function are implicitly global.

27. How can you share global variables across modules?


To share global variables across modules within a single program, create a special module. Import the config module in all modules of your application. The module will be available as a global variable across modules.

28. Explain how can you make a Python Script executable on Unix?To make a Python Script executable on Unix, you need to do two things?


Script file’s mode must be executable and

  • the first line must begin with # ( #!/usr/local/bin/python)

29. Explain how to delete a file in Python?


  • By using a command os.remove (filename) or os.unlink(filename)

30. Explain how can you generate random numbers in Python?


To generate random numbers in Python, you need to import command as import random

  • random.random()

This returns a random floating point number in the range [0,1)

31. Explain how can you access a module written in Python from C?


You can access a module written in Python from C by following method,

  • Module = =PyImport_ImportModule(“”);

32. Mention the use of // operator in Python?


It is a Floor Divisionoperator , which is used for dividing two operands with the result as quotient showing only digits before the decimal point. For instance, 10//5 = 2 and 10.0//5.0 = 2.0.

33. Mention five benefits of using Python?


1.Python comprises of a huge standard library for most Internet platforms like Email, HTML, etc.

2.Python does not require explicit memory management as the interpreter itself allocates the memory to new variables and free them automatically

3.Provide easy readability due to use of square brackets Easy-to-learn for beginners

4.Having the built-in data types saves programming time and effort from declaring variables

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34. Mention the use of the split function in Python?


The use of the split function in Python is that it breaks a string into shorter strings using the defined separator. It gives a list of all words present in the string.

35. Explain what is Flask & its benefits?


Flask is a web micro framework for Python based on “Werkzeug, Jinja 2 and good intentions” BSD licensed. Werkzeug and jingja are two of its dependencies.

Flask is part of the micro-framework. Which means it will have little to no dependencies on external libraries. It makes the framework light while there is little dependency to update and less security bugs.

36. Mention what is the difference between Django, Pyramid, and Flask?


Flask is a “micro framework” primarily build for a small application with simpler requirements. In flask, you have to use external libraries. Flask is ready to use.

Pyramid are build for larger applications. It provides flexibility and lets the developer use the right tools for their project. The developer can choose the database, URL structure, templating style and more. Pyramid is heavy configurable.

Like Pyramid, Django can also used for larger applications. It includes an ORM.

37. Mention what is Flask-WTF and what are their features?


Flask-WTF offers simple integration with WTForms.

Features include for Flask WTF are

1.Integration with wtforms Secure form with csrf token Global csrf protection Internationalization integration Recaptcha supporting

2.File upload that works with Flask Uploads

38. Explain what is the common way for the Flask script to work?


The common way for the flask script to work is,

Either it should be the import path for your application Or the path to a Python file

39. Explain how you can access sessions in Flask?


A session basically allows you to remember information from one request to another. In a flask, it uses a signed cookie so the user can look at the session contents and modify. The user can modify the session if only it has the secret key Flask.secret_key.

40. Is Flask an MVC model and if yes give an example showing MVC pattern for your application?


Basically, Flask is a minimalistic framework which behaves same as MVC framework. So MVC is a perfect fit for Flask, and the pattern for MVC we will consider for the following example

  • from flask import Flaskapp = Flask(_name_)@app.route(“/”)Def hello():return “Hello World” = True)

In this code your,Configuration part will be from

  • flask import Flaskapp = Flask(_name_)View part will be@app.route(“/”)Def hello():return “Hello World”While you model or main part will = True)

41. What type of a language is python? Interpreted or Compiled?


Beginner’s Answer:

Python is an interpreted, interactive, object­oriented programming language.

Expert Answer:

Python is an interpreted language, as opposed to a compiled one, though thedistinction can be blurry because of the presence of the bytecode compiler. This meansthat source files can be run directly without explicitly creating an executable which isthen run.

42. What do you mean by python being an “interpreted language”? (Continues from previous question)


An interpreted language​is a programming language​for which most of itsimplementations execute instructions directly, without previously compiling a programinto machine­language​instructions. In context of Python, it means that Python programruns directly from the source code.

43. What is python’s standard way of identifying a block of code?



44. Please provide an example implementation of a function called “my_func” that returns the square of a given variable “x”. (Continues from previous question)


  • defmy_func(x):
  • returnx**2

45. Is python statically typed or dynamically typed?


​Dynamic.In a statically typed language, the type of variables must be known (and usually declared) at the point at which it is used. Attempting to use it will be an error. In a dynamically typed language, objects still have a type, but it is determined at runtime.You are free to bind names (variables) to different objects with a different type. So longas you only perform operations valid for the type the interpreter doesn’t care what typethey actually are.

46. Is python strongly typed or weakly typed language?


​Strong. In a weakly typed language a compiler / interpreter will sometimes change thetype of a variable. For example, in some languages (like JavaScript) you can addstrings to numbers ‘x’ + 3 becomes ‘x3’. This can be a problem because if you havemade a mistake in your program, instead of raising an exception execution will continuebut your variables now have wrong and unexpected values. In a strongly typedlanguage (like Python) you can’t perform operations inappropriate to the type of theobject ­ attempting to add numbers to strings will fail. Problems like these are easier todiagnose because the exception is raised at the point where the error occurs rather thanat some other, potentially far removed, place.

47. Create a unicode string in python with the string “This is a test string”?


  • some_variable=u’Thisisateststring’


  • some_variable=u”Thisisateststring”

48. What is the python syntax for switch case statements?


Python doesn’t support switch­case statements. You can use if­else statementsfor this purpose.

49. What is a lambda statement? Provide an example?


A lambda statement is used to create new function objects and then return them atruntime.


  • my_func=lambdax:x**2

creates a function called my_func that returns the square of the argumentpassed.

50.What is the output of the following program?


  • #!/usr/bin/python
  • deffun1(a):
  • print’a:’,a
  • a=33;
  • print’locala:’,a
  • a=100
  • fun1(a)
  • print’aoutsidefun1:’,a
  • Ans. Output:
  • a:100
  • locala:33
  • aoutsidefun1:100

51. What is the purpose of ​#!/usr/bin/python​on the first line in the abovecode? Is there any advantage?


By specifying #!/usr/bin/pythonyou specify exactly which interpreter will beused to run the script on a particular system. This is the hardcoded path to the pythoninterpreter for that particular system. The advantage of this line is that you can use aspecific python version to run your code.

52. What does this [x**2forxinrange(10)ifx%2==0] list comprehension do?


Creates the following list:


53.Do sets, dictionaries and tuples also support comprehensions?


Sets and dictionaries support it. However tuples are immutable and havegenerators but not comprehensions.

Set Comprehension:


  • r={xforxinrange(2,101)
  • ifnotany(x%y==0foryinrange(2,x))}

Dictionary Comprehension:

  • {i:jfori,jin{1:’a’,2:’b’}.items()}


  • {1:’a’,2:’b’}.items()returnsalistof2-Tuple.i

is the first elementof tuplej is the second.

54. What are some mutable and immutable data­types/data­structures in python


Mutable Types Immutable Types

  • Dictionary number
  • List boolean
  • string
  • tuple

55. What can you use Python generator functions for?


One of the reasons to use generator is to make the solution clearer for some kindof solutions.The other is to treat results one at a time, avoiding building huge lists of results that youwould process separated anyway.

56. When is not a good time to use python generators?


Use list instead of generator when:

  • You need to access the data multiple times (i.e. cache the results instead of recomputing them)
  • You need random access (or any access other than forward sequential order):
  • You need to join strings (which requires two passes over the data)
  • You are using PyPy which sometimes can’t optimize generator code as muchas it can with normal function calls and list manipulations.
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57. What’s your preferred text editor?


Emacs. Any alternate answer leads to instant disqualification of the applicant

58.When should you use generator expressions vs. list comprehensions in Python and vice-versa?


Iterating over the generator expression or the list comprehension will do the samething. However, the list comp will create the entire list in memory first while thegenerator expression will create the items on the fly, so you are able to use it for verylarge (and also infinite!) sequences.

59.What is a negative index in Python?


Python arrays and list items can be accessed with positive or negative numbers. A negative Index accesses the elements from the end of the list counting backwards.


  • a=[123]
  • printa[-3]
  • printa[-2]


1 and 2

60. What is the difference between range and xrange functions?


Range returns a list while xrange returns an xrange object which take thesame memory no matter of the range size. In the first case you have all items alreadygenerated (this can take a lot of time and memory). In Python 3 however, range isimplemented with xrange and you have to explicitly call the list function if you want toconvert it to a list.

61.How can I find methods or attributes of an object in Python?


Built­in dir() function of Python ,on an instance shows the instance variables aswell as the methods and class attributes defined by the instance’s class and all its baseclasses alphabetically. So by any object as argument to dir() we can find all themethods & attributes of the object’s class

62.What is the statement that can be used in Python if a statement is required syntactically but the program requires no action?



63. Do you know what is the difference between lists and tuples? Can you give me an example for their usage?


First list are mutable while tuples are not, and second tuples can be hashed be used as keys for dictionaries. As an example of their usage, tuples are used whenthe order of the elements in the sequence matters e.g. a geographic coordinates, “list”of points in a path or route, or set of actions that should be executed in specific order.Don’t forget that you can use them a dictionary keys. For everything else use lists.

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