Python Interview Questions and Answers
Category : News
Python Interview questions and Answers
In simple way Meaning of Analogy is “Similarity ” or compassion between one thing and other thing base d on some similarity
250 + Python interview Question and Answer
1.Explain Python
Python, a programming language that has modules, threads, automatic memory management, objects, and exceptions. Pythons are easy and simple to use, open-source, extensible, transferrable, and build-in data structure.
2) Which Is is the Shortest way to read a file ?
Two memory-efficient ways in ranked order (first
is best) –
use of with – supported from python 2.5 and above
2. use of yield if you really want to have control over how much to read
1.USE OF WITH
with is the nice and efficient pythonic way to read large files.
Advantages:
1) File object is automatically closed after exiting from with execution block.
2) Exception handling inside the with block. 3) memory for loop iterates through the f file object line by line. internally it does buffered IO (to optimized on costly IO operations) and memory management. with open(“x.txt”) as f: for line in f: do something with data.
3)The with statement handles opening and closing the file, including if an exception is raised in the inner block. The for line in f treats the file object f as an iterable, which automatically uses buffered IO and memory management so you don’t have to worry about large files.
USE OF YIELD
Sometimes one might want more fine-grained control over how much to read in each iteration. In that case use iter & yield. Note with this method one explicitly needs close the file at the end.
def readInChunks(fileObj, chunkSize=2048):
“””
Lazy function to read a file piece by piece.
Default chunk size: 2kB.
“””
while True:
data = fileObj.read(chunkSize)
if not data:
break
yield data
f = open(‘bigFile’)
for chuck in readInChunks(f):
do_something(chunk)
f.close()
3) Why is <__init__.py> module used in Python?
he <__init__.py> module can help in fulfilling following objectives.
1. It makes Python interpret directories as containing packages by excluding the ones with a common name such as string.
It grants a programmer with the control to decide which directory is a package and which is not.
However, the <__init__.py> can also be an empty file. It can then help in executing the initialization code for a package or setting the <__all__> variable.
4) What are the different methods Python provides for copying an object?
We can either use a “Shallow Copy” or follow a “Deep Copy” approach.
Shallow Copy method.
The content of an object (say dictionary) doesn’t get copied by value but by creating a new reference.
SHALLOW COPY METHOD.
>>> a = {1: [1,2,3]}
>>> b = a.copy()
>>> a, b
({1: [1, 2, 3]}, {1: [1, 2, 3]})
>>> a[1].append(4)
>>> a, b
({1: [1, 2, 3, 4]}, {1: [1, 2, 3, 4]})
1
2
3
4
5
6
7
>>> a = {1: [1,2,3]}
>>> b = a.copy()
>>> a, b
({1: [1, 2, 3]}, {1: [1, 2, 3]})
>>> a[1].append(4)
>>> a, b
({1: [1, 2, 3, 4]}, {1: [1, 2, 3, 4]})
DEEP COPY METHOD.
It copies all the contents by value.
>>> c = copy.deepcopy(a)
>>> a, c
({1: [1, 2, 3, 4]}, {1: [1, 2, 3, 4]})
>>> a[1].append(5)
>>> a, c
({1: [1, 2, 3, 4, 5]}, {1: [1, 2, 3, 4]})
1
2
3
4
5
6
>>> c = copy.deepcopy(a)
>>> a, c
({1: [1, 2, 3, 4]}, {1: [1, 2, 3, 4]})
>>> a[1].append(5)
>>> a, c
({1: [1, 2, 3, 4, 5]}, {1: [1, 2, 3, 4]})
5)How will you set a global variable inside a function?
You can use a global variable in other functions by declaring it as global in each function that assigns to it:
globvar = 0
def set_globvar_to_one():
global globvar # Needed to modify global
copy of globvar
globvar = 1
def print_globvar():
print globvar # No need for global
declaration to read value of globvar
set_globvar_to_one()
print_globvar() # Prints 1
1
2
3
4
5
6
7
8
I imagine the reason for it is that, since global variables are so dangerous, Python wants to make sure that you really know that’s what you’re playing with by explicitly requiring the global keyword.
6) forelse in python
Python has an interesting for statement which lets you specify an else suite.
In a construct like this one:
for i in foo:
if bar(i):
break
else:
baz()
the else suite is executed after the for, but only if the for terminates normally (not by a break).
Here’s some code written without for…else:
def contains_even_number(l):
“Prints whether or not the list l contains an even number.”
has_even_number = False
for elt in l:
if elt % 2 == 0:
has_even_number = True
break
if has_even_number:
print “list contains an even number”
else:
print “list does not contain an even number”
The equivalent code snippet below illustrates how the use of for…else lets you remove an extraneous flag variable from that loop:
def contains_even_number(l):
“Prints whether or not the list l contains an even number.”
for elt in l:
if elt % 2 == 0:
print “list contains an even number”
break
else:
print “list does not contain an even number”
Use your good judgment when deciding whether to use the for…else construct.
It’s not unequivocally better, but when there’s an asymmetry between the two possibilities, you can make your code more readable by using for…else to keep the “happy path” logic at the top and the exceptional/error case at the bottom
9) What is difference between c++ and Java ?
Interface
- Java is platform independent
- There are no pointers in java
- There is no operator overloading in java
- There is garbage collection in java
- Supports multithreading
- There are no templates in java
- There are no global variables in java
Abstract Class
- C++ is platform dependent.
- There are pointers in C++
- C ++ has operator overloading.
- There is no garbage collection
- Does’nt support multithreading
- There are templates in java
- There are global variables in c++
10) What is bytecode in java ?
JIT compiler stands for Just in time compiler. JIT compiler compiles byte code in to executable code . JIT a part of JVM .JIT cannot convert complete java program in to executable code it converts as and when it is needed during execution.
11) What is bytecode in java ?
When a javac compiler compiler compiles a class it generates .class file. This .class file contains set of instructions called byte code. Byte code is a machine independent language and contains set of instructions which are to be executed only by JVM. JVM can understand this byte codes.
12) Difference between this() and super() in java ?
this() is used to access one constructor from another with in the same class while super() is used to access superclass constructor. Either this() or super() exists it must be the first statement in the constructor.
13) What is a class ?
Classes are fundamental or basic unit in Object Oriented Programming .A class is kind of blueprint or template for objects. Class defines variables, methods. A class tells what type of objects we are creating. For example take Department class tells us we can create department type objects. We can create any number of department objects.
All programming constructs in java reside in class. When JVM starts running it first looks for the class when we compile. Every Java application must have atleast one class and one main method. Class starts with class keyword. A class definition must be saved in class file that has same as class name. File name must end with .java extension.
public class FirstClass
{public static void main(String[] args)
{System.out.println(“My First class”);
}
}
If we see the above class when we compile JVM loads the FirstClass and generates a .class file(FirstClass.class). When we run the program we are running the class and then executes the main method.
14) What is an object ?
An Object is instance of class. A class defines type of object. Each object belongs to some class.Every object contains state and behavior. State is determined by value of attributes and behavior is called method. Objects are alos called as an instance.
To instantiate the class we declare with the class type.
public classFirstClass {public static voidmain(String[] args)
{
FirstClass f=new FirstClass();
System.out.println(“My First class”);
}
}
To instantiate the FirstClass we use this statement
FirstClass f=new FirstClass();
f is used to refer FirstClass object
15) What is an object ?
It contains the executable body that can be applied to the specific object of the class.
Method includes method name, parameters or arguments and return type and a body of executable code.
Syntax : type methodName(Argument List){
}
ex : public float add(int a, int b, int c) methods can have multiple arguments. Separate with commas when we have multiple arguments.
16) What is encapsulation ?
The process of wrapping or putting up of data in to a single unit class and keeps data safe from misuse is called encapsulation .
Through encapsulation we can hide and protect the data stored in java objects.Java supports encapsulation through access control. There are four access control modifiers in java public , private ,protected and default level.
For example take a car class , In car we have many parts which is not required for driver to know what all it consists inside. He is required to know only about how to start and stop the car. So we can expose what all are required and hide the rest by using encapsulation.
17) Why main() method is public, static and void in java ?
public : “public” is an access specifier which can be used outside the class. When main method is declared public it means it can be used outside class.
static : To call a method we require object. Sometimes it may be required to call a method without the help of object. Then we declare that method as static. JVM calls the main() method without creating object by declaring keyword static.
void : void return type is used when a method does’nt return any value . main() method does’nt return any value, so main() is declared as void.
Signature : public static void main(String[] args) {
18) Explain about main() method in java ?
Main() method is starting point of execution for all java applications.
public static void main(String[] args) {}
String args[] are array of string objects we need to pass from command line arguments.
Every Java application must have atleast one main method.
19)What is constructor in java ?
A constructor is a special method used to initialize objects in java.
we use constructors to initialize all variables in the class when an object is created. As and when an object is created it is initialized automatically with the help of constructor in java. We have two types of constructors
Default Constructor
Parameterized Constructor
Signature : public classname()
{
}
Signature : public classname(parameters list)
{
}
20) What is difference between length and length() method in java ?
length() : In String class we have length() method which is used to return the number of characters in string.
Ex : String str = “Hello World”;
System.out.println(str.length());
Str.length() will return 11 characters including space.
length : we have length instance variable in arrays which will return the number of values or objects in array.
For example :
String days[]={” Sun”,”Mon”,”wed”,”thu”,”fri”,”sat”};
Will return 6 since the number of values in days array is 6.
21) What is ASCII Code?
ASCII stands for American Standard code for Information Interchange. ASCII character range is 0 to 255. We can’t add more characters to the ASCII Character set. ASCII character set supports only English. That is the reason, if we see C language we can write c language only in English we can’t write in other languages because it uses ASCII code.
22) What is Unicode ?
Unicode is a character set developed by Unicode Consortium. To support all languages in the world Java supports Unicode values. Unicode characters were represented by 16 bits and its character range is 0-65,535.
Java uses ASCII code for all input elements except for Strings,identifiers, and comments. If we want to use Punjabi we can use Punjabi characters for identifiers.We can enter comments in Punjabi
23) What is Unicode ?
Character constant is enclosed in single quotes. String constants are enclosed in double quotes. Character constants are single digit or character. String Constants are collection of characters.
Ex :’2’, ‘A’
Ex : “Hello World”
24) What are constants and how to create constants in java?
Constants are fixed values whose values cannot be changed during the execution of program. We create constants in java using final keyword.
Ex : final int number =10;
final String str=”java-interview –questions”
25) Difference between ‘>>’ and ‘>>>’ operators in java?
>> is a right shift operator shifts all of the bits in a value to the right to a specified number of times.
int a =15;
a= a >> 3;
The above line of code moves 15 three characters right.
>>> is an unsigned shift operator used to shift right. The places which were vacated by shift are filled
with zeroes.
