All The Useful Python Interview Questions (New)

Basic Python Interview Questions

 

1. What are the key features of Python?
Python is one of the most popular programming languages used by data scientists and AIML professionals. This popularity is due to the following key features of Python:
- Python is easy to learn due to its clear syntax and readability
- Python is easy to interpret, making debugging easy
- Python is free and Open-source
- It can be used across different languages
- It is an object-oriented language which supports concepts of classes
- It can be easily integrated with other languages like C++, Java and more

2. What are Keywords in Python?
Keywords in Python are reserved words which are used as identifiers, function name or variable name. They help define the structure and syntax of the language. 
There are a total of 33 keywords in Python 3.7 which can change in the next version, i.e., Python 3.8. A list of all the keywords is provided below:

Keywords in Python
False    class    finally    is    return
None    continue    for    lambda    try
True    def    from    nonlocal    while
and    del    global    not    with
as    elif    if    or    yield
assert    else    import    pass    
break    except    

3. What are Literals in Python and explain about different Literals?
Literals in Python refer to the data that is given in a variable or constant. Python has various kinds of literals including:

String Literals: It is a sequence of characters enclosed in codes. There can be single, double and triple strings based on the number of quotes used. Character literals are single characters surrounded by single or double-quotes. 
Numeric Literals: These are unchangeable kind and belong to three different types - integer, float and complex.
Boolean Literals: They can have either of the two values- True or False which represents '1' and '0' respectively. 
Special Literals: Special literals are sued to classify fields that are not created. It is represented by the value 'none'.

4. How can you concatenate two tuples?

Solution: 
Let's say we have two tuples like this ->
tup1 = (1,'a',True)
tup2 = (4,5,6)

Concatenation of tuples means that we are adding the elements of one tuple at the end of another tuple.
Now, let's go ahead and concatenate tuple2 with tuple1:

Code
tup1=(1,"a",True)
tup2=(4,5,6)
tup1+tup2
Output

All you have to do is, use the '+' operator between the two tuples and you'll get the concatenated result.

Similarly, let's concatenate tuple1 with tuple2:

Code
tup1=(1,"a",True)
tup2=(4,5,6)
tup2+tup1
Output

5. What are functions in Python?
Functions in Python refer to blocks that have organised, and reusable codes to perform single, and related events. Functions are important to create better modularity for applications which reuse high degree of coding. Python has a number of built-in functions like print(). However, it also allows you to create user-defined functions.

6. How to Install Python?
To Install Python, first go to Anaconda.org and click on 'Download Anaconda'. Here, you can download the latest version of Python. After Python is installed, it is a pretty straightforward process. The next step is to power up an IDE and start coding in Python. 

7. What is Python Used For?
Python is one of the most popular programming languages in the world today. Whether you're browsing through Google, scrolling through Instagram, watching videos on YouTube, or listening to music on Spotify, all of these applications make use of Python for their key programming requirements. Python is used across various platforms, applications, and services such as web development.

8. How can you initialize a 5*5 numpy array with only zeroes?
Solution: 
We will be using the .zeros() method
import numpy as np
n1=np.zeros((5,5))
n1
Use np.zeros() and pass in the dimensions inside it. Since, we want a 5*5 matrix, we will pass (5,5) inside the .zeros() method.
 

9. What is Pandas?
Pandas is an open source python library which has a very rich set of data structures for data based operations. Pandas with it's cool features fits in every role of data operation, whether it be academics or solving complex business problems. Pandas can deal with a large variety of files and is one of the most important tools to have a grip on.

10. What are dataframes?
A pandas dataframe is a data structure in pandas which is mutable. Pandas has support for heterogeneous data which is arranged across two axes.( rows and columns).
Reading files into pandas:-

Import pandas as pd
df=p.read_csv('mydata.csv')

Here df is a pandas data frame. read_csv() is used to read a comma delimited file as a dataframe in pandas.

11. What is a Pandas Series?
Series is a one dimensional pandas data structure which can data of almost any type. It resembles an excel column. It supports multiple operations and is used for single dimensional data operations.

Creating a series from data:

Code
import pandas as pd
data=["1",2,"three",4.0]
series=pd.Series(data)
print(series)
print(type(series))
Output

12. What is pandas groupby?
A pandas groupby is a feature supported by pandas which is used to split and group an object.  Like the sql/mysql/oracle groupby it used to group data by classes, entities which can be further used for aggregation. A dataframe can be grouped by one or more columns.

Code
df = pd.DataFrame({'Vehicle':['Etios','Lamborghini','Apache200','Pulsar200'], 'Type':["car","car","motorcycle","motorcycle"]})
df
Output

To perform groupby type the following code:
df.groupby('Type').count()
Output

13. How to create a dataframe from lists?
To create a dataframe from lists ,

1. create an empty dataframe

2. add lists as individuals columns to the list

Code
df=pd.DataFrame()
bikes=["bajaj","tvs","herohonda","kawasaki","bmw"]
cars=["lamborghini","masserati","ferrari","hyundai","ford"]
df["cars"]=cars
df["bikes"]=bikes
df
Output

14. How to create data frame from a dictionary?
A dictionary can be directly passed as an argument to the DataFrame() function to create the data frame.

Code
import pandas as pd
bikes=["bajaj","tvs","herohonda","kawasaki","bmw"]
cars=["lamborghini","masserati","ferrari","hyundai","ford"]
d={"cars":cars,"bikes":bikes}
df=pd.DataFrame(d)
df
Output

15. How to combine dataframes in pandas?
Two different data frames can be stacked either horizontally or vertically by the concat(), append() and join() functions in pandas.
Concat works best when the dataframes have the same columns and can be used for concatenation of data having similar fields and is basically vertical stacking of dataframes into a single dataframe.
Append() is used for horizontal stacking of dataframes. If two tables(dataframes) are to be merged together then this is the best concatenation function.
Join is used when we need to extract data from different dataframes which are having one or more common columns. The stacking is horizontal in this case.
 

16. What kind of joins does pandas offer?
Pandas has a left join, inner join, right join and an outer join.

17. How to merge dataframes in pandas?
Merging depends on the type and fields of different dataframes being merged. If data is having similar fields data is merged along axis 0 else they are merged along axis 1.

18. Give the below dataframe drop all rows having Nan.
The dropna function can be used to do that.
df.dropna(inplace=True)
df
Output

19. How to access the first five entries of a dataframe?
By using the head(5) function we can get the top five entries of a dataframe. By default df.head() returns the top 5 rows. To get the top n rows df.head(n) will be used.

20. How to access the last five entries of a dataframe?
By using tail(5) function we can get the top five entries of a dataframe. By default df.tail() returns the top 5 rows. To get the last n rows df.tail(n) will be used.

21. How to fetch a data entry from a pandas dataframe using a given value in index?
To fetch a row from dataframe given index x, we can use loc.
Df.loc[10] where 10 is the value of the index.

Code
import pandas as pd
bikes=["bajaj","tvs","herohonda","kawasaki","bmw"]
cars=["lamborghini","masserati","ferrari","hyundai","ford"]
d={"cars":cars,"bikes":bikes}
df=pd.DataFrame(d)
a=[10,20,30,40,50]
df.index=a
df.loc[10]
Output

22. What are comments and how can you add comments in Python?
Comments in Python refer to a piece of text intended for information. It is especially relevant when more than one person works on a set of codes. It can be used to analyse code, leave feedback, and debug it. There are two types of comments which includes:
Single-line comment
Multiple-line comment
Codes needed for adding comment
#Note - single line comment
'''Note
Note
Note''' - - multiline comment

23. What is the difference between list and tuples in Python?
Lists are mutable, but tuples are immutable.

24. What is dictionary in Python? Give an example.
A Python dictionary is a collection of items in no particular order. Python dictionaries are written in curly brackets with keys and values. Dictionaries are optimised to retrieve value for known keys.
Example
d={'a':1,'b':2}

25. Find out the mean, median and standard deviation of this numpy array -> np.array([1,5,3,100,4,48])
import numpy as np
n1=np.array([10,20,30,40,50,60])
print(np.mean(n1))
print(np.median(n1))
print(np.std(n1))

26. What is a classifier?
A classifier is used to predict the class of any data point. Classifiers are special hypotheses that are used to assign class labels to any particular data points. A classifier often uses training data to understand the relation between input variables and the class. Classification is a method used in supervised learning in Machine Learning.

27. In Python how do you convert a string into lowercase?
All the upper cases in a string can be converted into lowercase by using the method: string.lower()
ex: string = 'FATSKILLS' print(string.lower())
o/p: fatskills

28. How do you get a list of all the keys in a dictionary?
One of the ways we can get a list of keys is by using: dict.keys()
This method returns all the available keys in the dictionary. dict = {1:a, 2:b, 3:c} dict.keys()
o/p: [1, 2, 3]

29. How can you capitalize the first letter of a string?
We can use the capitalize() function to capitalize the first character of a string. If the first character is already in capital then it returns the original string.
Syntax: string_name.capitalize() ex: n = 'fatskills' print(n.capitalize())
o/p: Fatskills

30. How can you insert an element at a given index in Python?
Python has an inbuilt function called the insert() function.
It can be used used to insert an element at a given index.
Syntax: list_name.insert(index, element)
ex: list = [ 0,1, 2, 3, 4, 5, 6, 7 ]
#insert 10 at 6th index
list.insert(6, 10)
o/p: [0,1,2,3,4,5,10,6,7]

31. How will you remove duplicate elements from a list?
There are various methods to remove duplicate elements from a list. But, the most common one is, converting the list into a set by using the set() function and using the list() function to convert it back to a list, if required. ex: list0 = [2, 6, 4, 7, 4, 6, 7, 2]
list1 = list(set(list0)) print ('The list without duplicates : ' + str(list1)) o/p: The list without duplicates : [2, 4, 6, 7]

32. What is recursion?
Recursion is a function calling itself one or more times in it body. One very important condition a recursive function should have to be used in a program is, it should terminate, else there would be a problem of an infinite loop.

33. Explain Python List Comprehension.
List comprehensions are used for transforming one list into another list. Elements can be conditionally included in the new list and each element can be transformed as needed. It consists of an expression leading a for clause, enclosed in brackets. for ex: list = [i for i in range(1000)]
print list

34. What is the bytes() function?
The bytes() function returns a bytes object. It is used to convert objects into bytes objects, or create empty bytes object of the specified size.

35. What are the different types of operators in Python?
Python has the following basic operators:
Arithmetic( Addition(+), Substraction(-), Multiplication(*), Division(/), Modulus(%) ), Relational ( <, >, <=, >=, ==, !=, ),
Assignment ( =. +=, -=, /=, *=, %= ),
Logical ( and, or not ), Membership, Identity, and Bitwise Operators

36. What is the 'with statement'?
'with' statement in python is used in exception handling. A file can be opened and closed while executing a block of code, containing the 'with' statement., without using the close() function. It essentially makes the code much more easy to read.

37. What is a map() function in Python?
The map() function in Python is used for applying a function on all elements of a specified iterable. It consists of two parameters, function and iterable. The function is taken as an argument and then applied to all the elements of an iterable(passed as the second argument). An object list is returned as a result.
def add(n):
return n + n number= (15, 25, 35, 45)
res= map(add, num)
print(list(res))
o/p: 30,50,70,90

38. What is __init__ in Python?
_init_ methodology is a reserved method in Python aka constructor in OOP. When an object is created from a class and _init_ methodolgy is called to acess the class attributes.

39. What are the tools present to perform statics analysis?
The two static analysis tool used to find bugs in Python are: Pychecker and Pylint. Pychecker detects bugs from the source code and warns about its style and complexity.While, Pylint checks whether the module matches upto a coding standard.

40. What is the difference between tuple and dictionary?
One major difference between a tuple and a dictionary is that dictionary is mutable while a tuple is not. Meaning the content of a dictionary can be changed without changing it's identity, but in tuple that's not possible.

41. What is pass in Python?
Pass is a statement which does nothing when executed. In other words it is a Null statement. This statement is not ignored by the interpreter, but the statement results in no operation. It is used when you do not want any command to execute but a statement is required.

42. How can an object be copied in Python?
Not all objects can be copied in Python, but most can. We ca use the '=' operator to copy an obect to a variable.
ex: var=copy.copy(obj)

43. How can a number be converted to a string?
The inbuilt function str() can be used to convert a nuber to a string.

44. What are module and package in Python?
Modules are the way to structure a program. Each Python program file is a module, importing other attributes and objects. The folder of a program is a package of modules. A package can have modules or subfolders.

45. What is object() function in Python?
In Python the object() function returns an empty object. New properties or methods cannot be added to this object.

46. What is the difference between NumPy and SciPy?
NumPy stands for Numerical Python while SciPy stands for Scientific Python. NumPy is the basic library for defining arrays and simple mathematica problems, while SciPy is used for more complex problems like numerical integration and optimization and machine learning and so on.

47. What does len() do?
len() is used to determine the length of a string, a list, an array, and so on. ex: str = 'greatlearning'
print(len(str))
o/p: 13

48. Define encapsulation in Python.
Encapsulation means binding the code and the data together. A Python class for example.

49. What is the type () in Python?
type() is a built-in method which either returns the type of the object or returns a new type object based on the arguments passed.
ex: a = 100
type(a)
o/p: int

50. What is split() function used for?
Split fuction is used to split a string into shorter string using defined seperatos. letters = (' A, B, C')
n = text.split(',')
print(n)
o/p: ['A', 'B', 'C' ]

51. What are the built-in types does python provide?
Python has following built-in data types:

Numbers: Python identifies three types of numbers:
Integer: All positive and negative numbers without a fractional part
Float: Any real number with floating-point representation
Complex numbers: A number with a real and imaginary component represented as x+yj. x and y are floats and j is -1(square root of -1 called an imaginary number)
Boolean: The Boolean data type is a data type that has one of two possible values i.e. True or False. Note that 'T' and 'F' are capital letters.
String: A string value is a collection of one or more characters put in single, double or triple quotes.
List: A list object is an ordered collection of one or more data items which can be of different types, put in square brackets. A list is mutable and thus can be modified, we can add, edit or delete individual elements in a list.
Set: An unordered collection of unique objects enclosed in curly brackets
Frozen set: They are like a set but immutable, which means we cannot modify their values once they are created.
Dictionary: A dictionary object is unordered in which there is a key associated with each value and we can access each value through its key. A collection of such pairs is enclosed in curly brackets. For example {'First Name' : 'Tom' , 'last name' : 'Hardy'} Note that Number values, strings, and tuple are immutable while as List or Dictionary object are mutable.

52. What is docstring in Python?
Python docstrings are the string literals enclosed in triple quotes that appear right after the definition of a function, method, class, or module. These are generally used to describe the functionality of a particular function, method, class, or module. We can access these docstrings using the __doc__ attribute. Here is an example:

def square(n):
   '''Takes in a number n, returns the square of n'''
   return n**2
print(square.__doc__)
Ouput: Takes in a number n, returns the square of n.

53. How to Reverse a String in Python?
In Python, there are no in-built functions that help us reverse a string. We need to make use of an array slicing operation for the same.

str_reverse = string[::-1]
Learn more: How To Reverse a String In Python

54. How to check Python Version in CMD?
To check the Python Version in CMD, press CMD + Space. This opens Spotlight. Here, type 'terminal' and press enter. To execute the command, type python - version or python -V and press enter. This will return the python version in the next line below the command.

55. Is Python case sensitive when dealing with identifiers?
Yes. Python is case sensitive when dealing with identifiers. It is a case sensitive language. Thus, variable and Variable would not be the same.

Python Interview Questions for Experienced Professionals

1. How to create a new column in pandas by using values from other columns?
We can perform column based mathematical operations on a pandas dataframe. Pandas columns containing numeric values can be operated upon by operators.
Code
import pandas as pd
a=[1,2,3]
b=[2,3,5]
d={"col1":a,"col2":b}
df=pd.DataFrame(d)
df["Sum"]=df["col1"]+df["col2"]
df["Difference"]=df["col1"]-df["col2"]
df
Output
pandas

2. What are the different functions that can be used by grouby in pandas?
grouby() in pandas can be used with multiple aggregate functions. Some of which are sum(),mean(), count(),std().
Data is divided into groups based on categories and then the data in these individual groups can be aggregated by the aforementioned functions.

3. How to select columns in pandas and add them to a new dataframe? What if there are two columns with the same name?
If df is dataframe in pandas df.columns gives the list of all columns. We can then form new columns by selecting columns.
If there are two columns with the same name then both columns get copied to the new dataframe.
Code
print(d_new.columns)
d=d_new[["col1"]]
d
Output
output

4. How to delete a column or group of columns in pandas? Given the below dataframe drop column 'col1'.
drop() function can be used to delete the columns from a dataframe. 
d={"col1":[1,2,3],"col2":["A","B","C"]}
df=pd.DataFrame(d)
df=df.drop(["col1"],axis=1)
df
Output

5. Given the following data frame drop rows having column values as A.
Code
d={"col1":[1,2,3],"col2":["A","B","C"]}
df=pd.DataFrame(d)
df.dropna(inplace=True)
df=df[df.col1!=1]
df
Output

6. Given a dataset find the highest paid player in each college in each team.
df.groupby(["Team","College"])["Salary"].max()

7. Given a dataset find the min max and average salary of a player collegewise and teamwise.
Code
df.groupby(["Team","College"])["Salary"].max.agg([('max','max'),('min','min'),('count','count'),('avg','min')])
Output

8. What is reindexing in pandas?
Reindexing is the process of re-assigning the index of a pandas dataframe.
Code
import pandas as pd
bikes=["bajaj","tvs","herohonda","kawasaki","bmw"]
cars=["lamborghini","masserati","ferrari","hyundai","ford"]
d={"cars":cars,"bikes":bikes}
df=pd.DataFrame(d)
a=[10,20,30,40,50]
df.index=a
df
Output

9. What do you understand by lambda function? Create a lambda function which will print the sum of all the elements in this list -> [5, 8, 10, 20, 50, 100]
from functools import reduce
sequences = [5, 8, 10, 20, 50, 100]
sum = reduce (lambda x, y: x+y, sequences)
print(sum)

10. What is vstack() in numpy? Give an example
vstack() is a function to align rows vertically. All rows must have same number of elements.

Code
import numpy as np
n1=np.array([10,20,30,40,50])
n2=np.array([50,60,70,80,90])
print(np.vstack((n1,n2)))
Output

11. How do we interpret Python?
When a python program is written, it converts the source code written by the developer into intermediate language, which is then coverted into machine language that needs to be executed.

12. How to remove spaces from a string in Python?
Spaces can be removed from a string in python by using strip() or replace() functions. Strip() function is used to remove the leading and trailing white spaces while the replace() function is used to remove all the white spaces in the string:
string.replace(' ','') ex1: str1= 'fat skills'
print (str.strip())
o/p: fat skills
ex2: str2='fat skills'
print (str.replace(' ',''))
o/p: fatskills

13. Explain the file processing modes that Python supports.
There are three file processing modes in Python: read-only(r), write-only(w), read-write(rw) and append (a). So, if you are opening a text file in say, read mode. The preceding modes become 'rt' for read-only, 'wt' for write and so on. Similarly, a binary file can be opened by specifying 'b' along with the file accessing flags ('r', 'w', 'rw' and 'a') preceding it.

14. What is pickling and unpickling?
Pickling is the process of converting a Python object hierarchy into a byte stream for storing it into a database. It is also known as serialization. Unpickling is the reverse of pickling. The byte stream is converted back into an object hierarchy.

15. How is memory managed in Python?
Memory management in python comprises of a private heap containing all objects and data stucture. The heap is managed by the interpreter and the programmer does not have acess to it at all. The Python memory manger does all the memory allocation. Moreover, there is an inbuilt garbage collector that recycles and frees memory for the heap space.

16. What is unittest in Python?
Unittest is a unit testinf framework in Python. It supports sharing of setup and shutdown code for tests, aggregation of tests into collections,test automation, and independence of the tests from the reporting framework.

17. How do you delete a file in Python?
Files can be deleted in Python by using the command os.remove (filename) or os.unlink(filename)

18. How do you create an empty class in Python?
To create an empty class we can use the pass command after the definition of the class object. A pass is a statement in Python that does nothing.

19. What are Python decorators?
Decorators are functions that take another functions as argument to modify its behaviour without changing the function itself. These are useful when we want to dynamically increase the functionality of a function without changing it. Here is an example :
def smart_divide(func):
   def inner(a, b):
       print("Dividing", a, "by", b)
       if b == 0:
           print("Make sure Denominator is not zero")
           return
return func(a, b)
   return inner
@smart_divide
def divide(a, b):
   print(a/b)
divide(1,0)

Here, smart_divide is a decorator function that is used to add functionality to simple divide function.

 

Python OOPS Interview Questions

1. What do you understand by object oriented programming in Python?
Object oriented programming refers to the process of solving a problem by creating objects. This approach takes into account two key factors of an object- attributes and behaviour.

2. How are classes created in Python? Give an example
class Node(object):
 def __init__(self):
   self.x=0
   self.y=0

Here, Node is a class.

3. What is inheritance in Object oriented programming? Give an example of multiple inheritance.
Inheritance is one of the core concepts of object-oriented programming. It is a process of deriving a class from a different class and form a hierarchy of classes that share the same attributes and methods. It is generally used for deriving different kinds of exceptions, create custom logic for existing frameworks and even map domain models for database.

Example:
class Node(object):
 def __init__(self):
   self.x=0
   self.y=0
Here, class Node inherits from the object class.
 

4. What is multi-level inheritance? Give an example for multi-level inheritance?
If class A inherits from B and C inherits from A it's called multilevel inheritance.

class B(object):
 def __init__(self):
   self.b=0

class A(B):
 def __init__(self):
   self.a=0

class C(A):
 def __init__(self):
   self.c=0
 

 

Also see: Useful Python Programs for Interviews
All The Useful Python Interview Questions & Answers (For Beginners / Intermediate)