4/9/19

Python Interview Questions and Answers Part-2


29)  Tell me about a few string operations in Python?
Here are the most commonly used text processing methods.

#Creating strings
name = "John" # a string
mychar = 'S' # a character
print(name)
print(mychar)

#you can also use the following syntax to create strings.
name1 = str() # this will create empty string object
name2 = str("newstring") # string object containing 'newstring'
print(name1)
print(name2)

#====Strings are immutable====
str1="welcome"
str2="welcome"

print(id(str1),id(str2))  #57660416 ,57660416

str2=str2+"to python"
print(id(str1),id(str2))  #57660416 ,59955200(changed means immutable)

#==== + and * with string=====
str="welcome"
print(str+" to Python programming") # welcome to Python programming
print(str *3) #welcomewelcomewelcome

#=======Slicing ==============
str="welcome"
print(str[1:3]) #el
print(str[:6])#welcom
print(str[4:])#ome
print(str[1:-1]) #elcom #elimate 1 char from end
print(str[1:-2]) #elco  #eleminate 2 chars from end

#=======String Functions in Python=======
print(len("hello")) #5
print(max("abc")) #c
print(min("abc")) #a

#========in  and not in  operators=====
s1 = "Welcome"
print("come" in s1)# True
print("come" not in s1) #False

#========Strings comparison=======
print("tim" == "tie") #False
print("free" != "freedom") #True
print ("arrow" > "aron") #True
print ("right" >= "left") #True
print ("teeth" < "tee") #False
print ("yellow" <= "fellow") #False
print ("abc" > "") #True

#======Testing strings===========
s = "welcome to python"
print(s.isalnum()) #False
print("Welcome".isalpha()) #True
print("2012".isdigit()) #True
print("first Number".isidentifier())#False
print(s.islower()) #True
print("WELCOME".isupper()) #True
print(" ".isspace()) #True

#======Searching for Substrings========
s = "welcome to python"
print(s.endswith("thon")) #True
print(s.startswith("good")) #False
print(s.find("come")) #3
print(s.find("become")) #-1
print(s.count("o")) #3

#=========Converting Strings==========
s = "String in PYTHON"
s1 = s.capitalize()
print(s1) #String in python

s2 = s.title()
print(s2)#String In Python

s3 = s.lower()
print(s3) #string in python

s4 = s.upper()
print(s4) #STRING IN PYTHON

s5 = s.swapcase()
print(s5) #sTRING IN python

s6 = s.replace("in", "on")
print(s6) #String on PYTHON

print(s) #String in PYTHON

30) How do you create a list which is a reverse version on another list in Python?
Python provides a function called reversed(), which will return a reversed iterator. Then, one can use a list constructor over it to get a list.

Example:
a =[10,20,30,40,50]
print(a)
b = list(reversed(a))#[10, 20, 30, 40, 50]
print(b) #[50, 40, 30, 20, 10]

31) What is a dictionary in Python?
In Python, dictionaries are kind of hash or maps in another language. Dictionary consists of a key and a value. Keys are unique, and values are accessed using keys. Here are a few examples of creating and accessing dictionaries.

Examples:

######Retrieving, modifying and adding elements in the dictionary########
friends = {'tom' : '111-222-333','jerry' : '666-33-111'}
print(friends) #{'tom': '111-222-333', 'jerry': '666-33-111'}

#Retrieving elements from the dictionary
print(friends['tom']) # 111-222-333

#Adding elements into the dictionary
friends['bob'] = '888-999-666'
print(friends) #{'tom': '111-222-333', 'jerry': '666-33-111', 'bob': '888-999-666'}

#Modify elements into the dictionary
friends['bob'] = '888-999-777'
print(friends) #{'tom': '111-222-333', 'jerry': '666-33-111', 'bob': '888-999-777'}

#Delete element from the dictionary
del friends['bob']
print(friends) #{'tom': '111-222-333', 'jerry': '666-33-111'}

32) How do you merge one dictionary with the other?
Python provides an update() method which can be used to merge one dictionary on another.
Example:
a = {'a':1}
b = {'b':2}
a.update(b)
print(a) #{'a': 1, 'b': 2}

33) How to walk through a list in a sorted order without sorting the actual list?
In Python we have function called sorted(), which returns a sorted list without modifying the original list. 

Here is the code:

a=[500,300,400,200,100]
print(a)#[500, 300, 400, 200, 100]
print(sorted(a)) #[100, 200, 300, 400, 500]

34) names = [‘john’, ‘fan’, ‘sam’, ‘megha’, ‘popoye’, ’tom’, ‘jane’, ‘james’,’tony’]
       Write one line of code to get a list of names that start with character ‘j’?
Solution:
names = ['john', 'fan', 'sam', 'megha', 'popoye', 'tom', 'jane', 'james', 'tony']
jnames=[name for name in names if name[0] == 'j']     #One line code to filter names that start with ‘j’
print(jnames)

35) What is a set?
A Set is an unordered collection of unique objects.

36) a = “this is a sample string with many characters”
      Write a Python code to find how many different characters are present in this string?
Solution:
a = "this is a sample string with many characters"
print(len(set(a))) #16

37) Name some standard Python errors you know?
TypeError: Occurs when the expected type doesn’t match with the given type of a variable.
ValueError: When an expected value is not given- if you are expecting 4 elements in a list and you gave 2.
NameError: When trying to access a variable or a function that is not defined.
IOError: When trying to access a file that does not exist. 
IndexError: Accessing an invalid index of a sequence will throw an IndexError.
KeyError: When an invalid key is used to access a value in the dictionary.

38) How Python supports encapsulation with respect to functions?
Python supports inner functions. A function defined inside a function is called an inner function, whose behavior is not hidden. This is how Python supports encapsulation with respect to functions.

39) How do you open an already existing file and add content to it?
In Python, open(,) is used to open a file in different modes. The open function returns a handle to the file, using which one can perform read, write and modify operations.

Example:

    F = open(“simplefile.txt”,”a+”) #Opens the file in append mode
    F.write(“some content”)    #Appends content to the file.
    F.close()    # closes the file.

39) 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

40) 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.

41) Explain how can you generate random numbers in Python?
To generate random numbers in Python, you need to import command as
import random
print(random.random())
This returns a random floating point number in the range [0,1)

42) How to connect to the Oracle Database using python script?
Using cx_Oracle module.

Example:

import os
import cx_Oracle
# Set folder in which Instant Client is installed in system path
os.environ['PATH'] = 'E:\\app\\OracleHomeUser1\\instantclient_18_3'
# Connect to hr account in Oracle Database 11g Express Edition
con = cx_Oracle.connect("hr", "hr", "localhost:1521/pdborcl")
cur = con.cursor()
query="select * from employees"
cur.execute(query)
for cols in cur:
    print(cols[0],"  ",cols[1],"  ",cols[2])
print("Completed!!!")
cur.close()
con.close()

43) How to connect to the Microsoft Excel and read write data in to excel using python script?

Reading data from Excel:

# import openpyxl module
import openpyxl

# Give the location of the file
path = "C:\SeleniumPractice\data3.xlsx"

workbook = openpyxl.load_workbook(path)
sheet = workbook["Sheet1"]

rows=sheet.max_row
cols=sheet.max_column

print(rows) # print the total number of rows
print(cols) # ptint total number of column

for r in range(1,rows+1):
    for c in range(1,cols+1):
        print(sheet.cell(row=r, column=c).value,end='     ')
    print()

Writing  data into Excel:

# import openpyxl module
import openpyxl

# Give the location of the file
path = "C:\SeleniumPractice\Test2.xlsx"

workbook = openpyxl.load_workbook(path)
sheet= workbook.active

for r in range(1,5):
    for c in range(1,3):
        sheet.cell(row=r, column=c).value = "abcdef" #(or)sheet.cell(row=r, column=c, value='xyz')

workbook.save(path)

44) What is the difference between list and 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 list.
Syntax: list_1 = [10, ‘Chelsea’, 20]
Syntax: tup_1 = (10, ‘Chelsea’ , 20)

45). Explain Inheritance in Python with an example.
Inheritance allows One class to gain all the members(say attributes and methods) of another class. Inheritance provides code reusability, makes it easier to create and maintain an application. The class from which we are inheriting is called super-class and the class that is inherited is called a derived / child class.

They are different types of inheritance supported by Python:
1. Single Inheritance – where a derived class acquires the members of a single super class.
2. Multi-level inheritance – a derived class d1 in inherited from base class base1, and d2 are inherited from base2.
3. Hierarchical inheritance – from one base class you can inherit any number of child classes
4. Multiple inheritance – a derived class is inherited from more than one base class.

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

Consider the example shown below:

from random import shuffle
x = ['Keep', 'The', 'Blue', 'Flag', 'Flying', 'High']
shuffle(x)
print(x)

47). Write a sorting algorithm for a numerical dataset in Python.
The following code can be used to sort a list in Python:

list = ["1", "4", "0", "6", "9"]
list = [int(i) for i in list]
list.sort()
print (list)

48) How to print current date &  time?
Time module is available.

Example:

import time;
localtime = time.asctime( time.localtime(time.time()) )
print ("Local current time :", localtime)




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