Python Interview Questions and answers

  • date 18th May, 2019 |
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Python Interview Questions and answers

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Python Interview Questions and answers for Fresher

 

What is Python?





 

Ans: Python is a powerful high-level object-oriented programming language. A great language for beginners because of its readability and other structural elements designed to make it easy to understand, Python is not limited to basic usage. In fact, it powers some of the world’s most complex applications and websites. First developed in the late 80s by Guido van Rossum, Python is currently in its third version, released in 2008, although the second version originally released in 2000 is still in common usage.
Python is an interpreter-based programming language, interactive and object-oriented scripting language. Python is designed to be highly readable. It is an interpreter based language which means that, unlike other languages like C and variants, the compilation doesn’t require before running. It’s dynamically typed, which means you need not to define the datatypes of the declared variables and anything like that.

 

What are the uses of Python?





 

Ans: Some of the uses of Python are :

1.Web Development: Python can be used to build server-side web applications. While a web framework is not required to build web apps, it’s rare that developers would not use existing open-source libraries to speed up their progress in getting their application working.
Python is not used in a web browser. The language executed in browsers such as Chrome, Firefox and Internet Explorer is JavaScript. Projects such as pyjs can compile from Python to JavaScript. However, most Python developers write their web applications using a combination of Python and JavaScript. Python is executed on the server-side while JavaScript is downloaded to the client and run by the web browser.

2.Software Development: Python is often used as a support language for software developers, to build control and management, testing, and in many other ways.

SCons for build control.

Buildbot and Apache Gump for automated continuous compilation and testing.

Roundup or Trac for bug tracking and project management.

Mathematics Calculation: Python can be used to perform various mathematical calculations such as addition, subtraction, Multiple and division. Another than these commands there are various mathematical which can be used such as :

1.abs(value) – absolute value
2.ceil(value) – rounds up
3.cos(value) – cosine, in radian
4.floor(value) – rounds down
5.log(value) – logarithm, base e
6.log10(value) – logarithm, base 10
7.max(value 1,value 2) – larger of two number
8.min(value 1,value 2) – smaller of two number
9.sqrt(value) – square root

 

System scripting: Scripting languages are often used to do repetitive, tedious work at a rate and with an accuracy that far surpasses what you could accomplish without them. All languages are tools. They are simply a means to get work done. They have value only insofar as they help you get your job done better. We believe that Python is a valuable tool, specifically because it enables you to get your work done efficiently.

So is Python better than Perl, Bash, Ruby, or any other language? It’s really difficult to put that sort of qualitative label on a programming language since the tool is so closely tied to the thought process of the programmer who is using it. Programming is a subjective, deeply personal activity. For the language to be excellent, it must fit the person using it.

 

What are the features of Python?





 

Ans: Some of the features of Python are :

Simple Language:

Coding in Python is very simple. A user with the non-coding background can easily learn this language if they have the good logical skill as python use basic English language for coding.

Free and Open Source:

Python is a freeware and open-source software so it can be easily downloaded and used. It doesn’t require any activation key or subscription to work on it.

Portability :

Python can run any operating system. Also, we use the python code written on one system onto another system without making any changes to the code.

Extensible and Embeddable:

This feature is provided to the user as to extend python from its initial state.

An extensible software program, for example, might support add-ons or plug-ins that add extra functionality to the program.

 

High-level Interpreted Language:

In this feature, the code executes instruction directly and freely, without previously compiling a program into machine language instructions.

Object-Oriented :

Python is object-oriented so it is organized around objects rather than “actions” and data rather than logic.

 

Python Demo for Beginners And Experienced

 

Differentiate between tuples and lists in python?





 

Ans: The major difference is tuples are immutable while a list is mutable. It means once you create tuple you cannot edit or make changes in the value in tuple while in a list we can edit the value in it.

         Tuples                                List
A tuple is a sequence of immutable  objects List are versatile datatype which are Mutable
The syntax for Tuples are shown by parenthesis {} Syntax for List is shown by square brackets []
They are of fixed length List can be of variable length
Eg: tup_1 = { 10,’john’,5} Eg :  list_1 = [10, ‘john’, 5]

 

What are the basic Data Types Supported by Python?

Ans: Numeric Data types: int, long, float, NoneType

String: str

Boolean: (True, False)

NoneType: None

 

What is a Variable in Python?

Ans: When we say Name = ‘Prwatech’ in Python, the name is not storing the value ‘Prwatech’. But, ‘Name’ acts as a tag to refer to the object ‘Prwatech’. The object has types in Python but variables do not, all variables are just tags. All identifiers are variables in Python. Variables never store any data in Python.

 

Python Tutorial for Beginners

 

Python Interview Questions and answers for Experienced

 

How Python is interpreted?

Ans: 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.

 

What is a dictionary in Python programming?





 

Ans: A dictionary is a data structure known as an associative array in Python which stores a collection of objects. The collection is a set of keys having a single associated value. We can call it a hash, a map, or a hashmap as it gets called in other programming languages.

 

What is the set object in Python?

Ans: Sets are unordered collection objects in Python. They store unique and immutable objects. Python has its implementation derived from mathematics.

 

What is the use of the dictionary in Python?

Ans: A dictionary has a group of objects (the keys) map to another group of objects (the values). A Python dictionary represents a mapping of unique Keys to Values.

They are mutable and hence will not change. The values associated with the keys can be of any Python types.

Python Commands Tutorials

 

What is the difference between list and tuples in Python?

LIST vs TUPLES
LIST TUPLES
Lists are mutable i.e they can be edited. Tuples are immutable (tuples are lists which can’t be edited).
Lists are slower than tuples. Tuples are faster than the list.
Syntax: list_1 = [10, ‘Chelsea’, 20] Syntax: tup_1 = (10, ‘Chelsea’, 20)

 

What are the key features of Python?

Python is an interpreted language. That means that, unlike languages like C and its variants, Python does not need to be
compiled before it is run. Other interpreted languages include PHP and Ruby.
Python is dynamically typed; this means that you don’t need to state the types of variables when you declare them or
anything like that. You can do things like x=111 and then x=”I’m a string” without error
Python is well suited to object-orientated programming in that it allows the definition of classes along with composition
and inheritance. Python does not have access specifiers (like C++’s public, private).
In Python, functions are first-class objects. This means that they can be assigned to variables, returned from other
functions and passed into functions. Classes are also first-class objects
Writing Python code is quick but running it is often slower than compiled languages. Fortunately, , Python allows the
inclusion of C based extensions so bottlenecks can be optimized away and often are. The numpy package is a good
example of this, it’s really quite quick because a lot of the number-crunching it does isn’t actually done by Python
Python finds use in many spheres – web applications, automation, scientific modeling, big data applications and many
more. It’s also often used as a “glue” code to get other languages and components to play nice.

 

What type of language is python? Programming or scripting?

Ans: Python is capable of scripting, but in general sense, it is considered as a general-purpose programming language. To know
more about Scripting, you can refer to the Python Scripting Tutorial.

 

How is Python an interpreted language?

Ans: An interpreted language is any programming language that is not in machine-level code before runtime. Therefore,
Python is an interpreted language.

 

What is pep 8?

Ans: PEP stands for Python Enhancement Proposal. It is a set of rules that specify how to format Python code for maximum
readability.

 

How is memory managed in Python?

Ans:

1. Memory management in python is managed by Python private heap space. All Python objects and data structures are
located in a private heap. The programmer does not have access to this private heap. The python interpreter takes care of
this instead.
2. The allocation of heap space for Python objects is done by Python’s memory manager. The core API gives access to some
tools for the programmer to code.
3. Python also has an inbuilt garbage collector, which recycles all the unused memory and so that it can be made available to
the heap space.

 

What is namespace in Python?

Ans: A namespace is a naming system used to make sure that names are unique to avoid naming conflicts.

 

What is PYTHONPATH?

Ans: It is an environment variable that is used when a module is imported. Whenever a module is imported, PYTHONPATH is
also looked up to check for the presence of the imported modules in various directories. The interpreter uses it to determine
which module to load.

 

What are python modules? Name some commonly used built-in modules in Python?

Ans: Python modules are files containing Python code. This code can either be function classes or variables. A Python module is
a .py file containing executable code.
Some of the commonly used built-in modules are:
os
sys
math
random
data time
JSON

 

What are local variables and global variables in Python?

Global Variables:
Variables declared outside a function or in global space are called global variables. These variables can be accessed by any
function in the program.
Local Variables:
Any variable declared inside a function is known as a local variable. This variable is present in the local space and not in the
global space.
Example:
a=2
def add():
b=3
c=a+b
print(c)
add()
Output: 5
When you try to access the local variable outside the function add(), it will throw an error.

 

Is python case sensitive?

Ans: Yes. Python is a case sensitive language.

 

What is type conversion in Python?

Ans: Type conversion refers to the conversion of one data type into another.
int() – converts any data type into integer type
􀃖oat() – converts any data type into 􀃖oat type
ord() – converts characters into integer
hex() – converts integers to hexadecimal
oct() – converts an integer to the octal
tuple() – This function is used to convert to a tuple.
set() – This function returns the type after converting to set.
list() – This function is used to convert any data type to a list type.
dict() – This function is used to convert a tuple of order (key, value) into a dictionary.
str() – Used to convert an integer into a string.
complex(real,imag) – This function converts real numbers to complex(real,imag) number.

 

How to install Python on Windows and set path variable?

Ans: To install Python on Windows, follow the below steps:
Install python from this link: https://www.python.org/downloads/
After this, install it on your PC. Look for the location where PYTHON has been installed on your PC using the following
command on your command prompt: cmd python.
Then go 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%

 

Is indentation required in python?

Ans: Indentation is necessary for Python. It specifies a block of code. All code within loops, classes, functions, etc is specified
within an indented block. It is usually done using four space characters. If your code is not indented necessarily, it will not
execute accurately and will throw errors as well.

 

What is the difference between Python Arrays and lists?

Ans: Arrays and lists, in Python, have the same way of storing data. But, arrays can hold only a single data type elements whereas
lists can hold any data type elements.
Example:
import array as arr
My_Array=arr.array(‘i’,[1,2,3,4])
My_list=[1,’abc’,1.20]
print(My_Array)
print(My_list)
Output:
array(‘i’, [1, 2, 3, 4]) [1, ‘abc’, 1.2]

 

What are functions in Python?

Ans: A function is a block of code which is executed only when it is called. To define a Python function, the def keyword is used.
Example:
def Newfunc():
print(“Hi, Welcome to Prwatech”)
Newfunc(); #calling the function
Output: Hi, Welcome to Prwatech

 

What is __init__?

Ans: __init__ is a method or constructor in Python. This method is automatically called to allocate memory when a new object/
the instance of a class is created. All classes have the __init__ method.
Here is an example of how to use it.
class Employee:
def __init__(self, name, age,salary):
self.name = name
self.age = age
self.salary = 20000
E1 = Employee(“XYZ”, 23, 20000)
# E1 is the instance of class Employee.
#__init__ allocates memory for E1.
print(E1.name)
print(E1.age)
print(E1.salary)
Output:
XYZ
23
20000

 

What is a lambda function?

Ans: An anonymous function is known as a lambda function. This function can have any number of parameters but, can have
just one statement.
Example:
a = lambda x,y : x+y
print(a(5, 6))
Output: 11

 

What is self in Python?

Ans: Self is an instance or an object of a class. In Python, this is explicitly included as the first parameter. However, this is not the
case in Java where it’s optional. It helps to differentiate between the methods and attributes of a class with local variables.
The self-variable in the init method refers to the newly created object while in other methods, it refers to the object whose
the method was called.

 

How does break, continue and pass work?

Break
Allows loop termination when some condition is met and the control is transferred
to the next statement.
Continue
Allows skipping some part of a loop when some specific condition is met and the
control is transferred to the beginning of the loop
Pass
Used when you need some block of code syntactically, but you want to skip its
execution. This is basically a null operation. Nothing happens when this is executed.

 

What does [::-1] do?

Ans: [::-1] is used to reverse the order of an array or a sequence.
For example:
import array as arr
My_Array=arr.array(‘i’,[1,2,3,4,5])
My_Array[::-1]
Output: array(‘i’, [5, 4, 3, 2, 1])
[::-1] reprints a reversed copy of ordered data structures such as an array or a list. the original array or list remains unchanged.

 

How can you randomize the items of a list in place in Python?

Ans: Consider the example shown below:
from random import shuffle
x = [‘Keep’, ‘The’, ‘Blue’, ‘Flag’, ‘Flying’, ‘High’]
shuffle(x)
print(x)
The output of the following code is as below.
[‘Flying’, ‘Keep’, ‘Blue’, ‘High’, ‘The’, ‘Flag’]

 

What are python iterators?

Ans: Iterators are objects which can be traversed through or iterated upon.

 

How can you generate random numbers in Python?

Ans: The random module is the standard module that is used to generate a random number. The method is defined as:
import random
.random()
The statement random. the random() method returns the floating-point number that is in the range of [0, 1). The function generates
random float numbers. The methods that are used with the random class are the bound methods of the hidden instances. The
instances of the Random can be done to show the multi-threading programs that create a different instance of individual
threads. The other random generators that are used in this are:
1. randrange(a, b): it chooses an integer and defines the range in-between [a, b). It returns the elements by selecting them
randomly from the range that is specified. It doesn’t build a range object.
2. uniform(a, b): it chooses a floating-point number that is defined in the range of [a,b).Iyt returns the floating-point number
3. normalvariate(mean, sdev): it is used for the normal distribution where the mu is a mean and the sdev is a sigma that is
used for standard deviation.
4. The Random class that is used and instantiated creates an independent multiple random number generator.

 

What is the difference between range & xrange?

Ans: For the most part, xrange and range are the exact same in terms of functionality. They both provide a way to generate a list
of integers for you to use, however you please. The only difference is that range returns a Python list object and x range returns
an xrange object.
This means that xrange doesn’t actually generate a static list at run-time as the range does. It creates the values as you need them
with a special technique called yielding. This technique is used with a type of object known as generators. That means that if you
have a really gigantic range you’d like to generate a list for, say one billion, xrange is the function to use.
This is especially true if you have a real memory sensitive system such as a cell phone that you are working with, as the range will
use as much memory as it can to create your array of integers, which can result in a Memory Error and crash your program. It’s a
memory hungry beast.

 

How do you write comments in python?

Ans: Comments in Python start with a # character. However, alternatively, at times, commenting is done using docstrings(strings
enclosed within triple quotes).
Example:
#Comments in Python start like this
print(“Comments in Python start with a #”)
Output: Comments in Python start with a #

 

What is pickling and unpickling?

Ans: 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.

 

What are the generators in python?

Ans: Functions that return an iterable set of items are called generators.

 

How will you capitalize the first letter of string?

Ans: In Python, the capitalize() method capitalizes the first letter of a string. If the string already consists of a capital letter at the
beginning, then, it returns the original string.

 

How will you convert a string to all lowercase?

Ans: To convert a string to lowercase, lower() function can be used.
Example:
stg=’ABCD’
print(stg.lower())
Output: abcd

 

How to comment on multiple lines in python?

Ans: Multi-line comments appear in more than one line. All the lines to be commented are to be prefixed by a #. You can also a
very good shortcut method to comment on multiple lines. All you need to do is hold the ctrl key and left-click in every place
wherever you want to include a # character and type a # just once. This will comment on all the lines where you introduced your
cursor.

 

What are docstrings in Python?

Ans: Docstrings are not actually comments, but, they are documentation strings. These docstrings are within triple quotes.
They are not assigned to any variable and therefore, at times, serve the purpose of comments as well.
Example:
“””
Using docstring as a comment.
This code divides 2 numbers
“””
x=8
y=4
z=x/y
print(z)
Output: 2.0

 

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

Ans: Operators are special functions. They 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

 

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

Ans: Help() and dir() both functions are accessible from the Python interpreter and used for viewing a consolidated dump of
built-in functions.
1. 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.
2. Dir() function: The dir() function is used to display the de􀃕ned symbols.

 

Whenever Python exits, why isn’t all the memory de-allocated?

Ans:
1. Whenever Python exits, especially those Python modules which are having circular references to other objects or the
objects that are referenced from the global namespaces are not always de-allocated or freed.
2. It is impossible to de-allocate those portions of memory that are reserved by the C library.
3. On exit, because of having its own e􀃞client clean up mechanism, Python would try to de-allocate/destroy every other
object.

 

What is a dictionary in Python?

Ans: The built-in data types in Python are called a dictionary. It defines a one-to-one relationship between keys and values. Dictionaries
contain a pair of keys and their corresponding values. Dictionaries are indexed by keys.
Let’s take an example:
The following example contains some keys. Country, Capital & PM. Their corresponding values are India, Delhi, and Modi
respectively.
dict={‘Country’:’India’,’Capital’:’Delhi’,’PM’:’Modi’}
print dict[Country]
India
print dict[Capital]
Delhi
print dict[PM]
Modi

 

How can the ternary operators be used in python?

Ans: The Ternary operator is the operator that is used to show the conditional statements. This consists of the true or false
values with a statement that has to be evaluated for it.
Syntax:
The Ternary operator will be given as:
[on_true] if [expression] else [on_false]x, y = 25, 50big = x if x < y else y
Example:
The expression gets evaluated like if x then big=y will be sent as a result.

 

What does this mean: *args, **kwargs? And why would we use it?

Ans: We use *args when we aren’t sure how many arguments are going to be passed to a function, or if we want to pass a stored
list or tuple of arguments to a function. **kwargs is used when we don’t know how many keyword arguments will be passed to a
function, or it can be used 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 wise.

 

What does len() do?

Ans: It is used to determine the length of a string, a list, an array, etc.
Example:
stg=’ABCD’
len(stg)

 

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

Ans: To modify the strings, Python’s “re” module is providing 3 methods. They are:
split() – uses a regex pattern to “split” a given string into a list.
sub() – finds all substrings where the regex pattern matches and then replace them with a different string
subn() – it is similar to sub() and also returns the new string along with the no. of replacements.

 

What are negative indexes and why are they used?

Ans: The sequences in Python are indexed and it consists of the positive as well as negative numbers. The numbers that are
positive uses ‘0’ that is uses as first index and ‘1’ as the second index and the process goes on like that.
The index for the negative number starts from ‘-1’ that represents the last index in the sequence and ‘-2’ as the penultimate index
and the sequence carries forward like the positive number.
The negative index is used to remove any new-line spaces from the string and allow the string to except the last character that is
given as S[:-1]. The negative index is also used to show the index to represent the string incorrect order.

 

What are Python packages?

Ans: Python packages are namespaces containing multiple modules.

 

How can files be deleted in Python?

Ans: To delete a file in Python, you need to import the OS Module. After that, you need to use the os.remove() function.
Example:
import os
os.remove(“xyz.txt”)

What are the built-in types of python?

Ans: Built-in types in Python are as follows –
Integers
Floating-point
Complex numbers
Strings
Boolean
Built-in functions

 

What advantages do NumPy arrays over (nested) Python lists?

Ans:
1. Python’s lists are efficient general-purpose containers. They support (fairly) efficient insertion, deletion, appending, and
concatenation, and Python’s list comprehensions make them easy to construct and manipulate.
2. They have certain limitations: they don’t support “vectorized” operations like elementwise addition and multiplication, and
the fact that they can contain objects of differing types mean that Python must store type information for every element,
and must execute type dispatching code when operating on each element.
3. NumPy is not just more efficient; it is also more convenient. You get a lot of vector and matrix operations for free, which
sometimes allow one to avoid unnecessary work. And they are also efficiently implemented.
4. NumPy array is faster and You get a lot built in with NumPy, FFTs, convolutions, fast searching, basic statistics, linear
algebra, histograms, etc.

 

How to add values to a python array?

Ans: Elements can be added to an array using the append(), extend() and the insert (i,x) functions.
Example:
a=arr.array(‘d’, [1.1 , 2.1 ,3.1] )
a.append(3.4)
print(a)
a.extend([4.5,6.3,6.8])
print(a)
a.insert(2,3.8)
print(a)
Output:
array(‘d’, [1.1, 2.1, 3.1, 3.4])
array(‘d’, [1.1, 2.1, 3.1, 3.4, 4.5, 6.3, 6.8])
array(‘d’, [1.1, 2.1, 3.8, 3.1, 3.4, 4.5, 6.3, 6.8])

How to remove values to a python array?

Ans: Array elements can be removed using pop() or remove() method. The difference between these two functions is that the
former returns the deleted value whereas the latter does not.
Example:
a=arr.array(‘d’, [1.1, 2.2, 3.8, 3.1, 3.7, 1.2, 4.6])
print(a.pop())
print(a.pop(3))
a.remove(1.1)
print(a)
Output:
4.6
3.1
array(‘d’, [2.2, 3.8, 3.7, 1.2])

 

Does Python have OOps concepts?

Ans: Python is an object-oriented programming language. This means that any program can be solved in python by creating an
object model. However, Python can be treated as procedural as well as structural language.

What is the difference between deep and shallow copy?

Ans: Shallow copy is used when a new instance type gets created and it keeps the values that are copied in the new instance.
Shallow copy is used to copy the reference pointers just like it copies the values. These references point to the original objects
and the changes made in any member of the class will also affect the original copy of it. Shallow copy allows faster execution of
the program and it depends on the size of the data that is used.
Deep copy is used to store the values that are already copied. Deep copy doesn’t copy the reference pointers to the objects. It
makes the reference to an object and the new object that is pointed by some other object gets stored. The changes made in the
original copy won’t affect any other copy that uses the object. Deep copy makes execution of the program slower due to making
certain copies for each object that is been called.

 

How is Multithreading achieved in Python?

Ans:
1. Python has a multi-threading package but if you want to multi-thread to speed your code up, then it’s usually not a good
idea to use it.
2. Python has a construct called the Global Interpreter Lock (GIL). The GIL makes sure that only one of your ‘threads’ can
execute at any one time. A thread acquires the GIL, does a little work, then passes the GIL onto the next thread.
3. This happens very quickly so to the human eye it may seem like your threads are executing in parallel, but they are really
just taking turns using the same CPU core.
4. All this GIL passing adds overhead to execution. This means that if you want to make your code run faster then using the
threading package often isn’t a good idea.

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