Python Practice Questions & Answers

Write short notes on the following:

Arrays in python can only contain elements of same data types i.e., data type of array should be homogeneous. It is a thin wrapper around C language arrays and consumes far less memory than lists. Lists in python can contain elements of different data types i.e., data type of lists can be heterogeneous. It has the disadvantage of consuming large memory.

import array
a = array.array('i', [1, 2, 3])
for i in a:
    print(i, end=' ')

OUTPUT:

 1 2 3

a = array.array('i', [1, 2, 'string'])

OUTPUT:

TypeError: an integer is required (got type str)

a = [1, 2, 'string']
for i in a:
   print(i, end=' ')

OUTPUT:

1 2 string

The if…elif…else statement is used in Python for decision making. Python if Statement Syntax

if test expression:
    statement(s)

Decorators are used to add some design patterns to a function without changing its structure. Decorators generally are defined before the function they are enhancing. To apply a decorator we first define the decorator function. Then we write the function it is applied to and simply add the decorator function above the function it has to be applied to. For this, we use the @ symbol before the decorator.

Constructors are generally used for instantiating an object. The task of constructors is to initialize(assign values) to the data members of the class when an object of the class is created. In Python the init() method is called the constructor and is always called when an object is created.

Inheritance allows us to define a class that inherits all the methods and properties from another class. Parent class is the class being inherited from, also called base class. Child class is the class that inherits from another class, also called derived class.

To create a class, use the keyword class:

Example

Create a class named MyClass, with a property named x:

class MyClass:
x = 5  X = 5

An Object is an instance of a Class. A class is like a blueprint while an instance is a copy of the class with actual values.

Now we can use the class named MyClass to create objects:

Example

Create an object named p1, and print the value of x:

p1 = MyClass()
print(p1.x)

a. input()

The input() function allows a user to insert a value into a program. input() returns a string value. You can convert the contents of an input using any data type. For instance, you can convert the value a user inserts to a floating-point number.

b. list()

A list is defined as an ordered, mutable, and heterogeneous collection of objects. Lists are contained within a collection of square brackets [ ].

c. pow()

The pow(X, y) function returns the value of x to the power of y (xy). If a third parameter is present, it returns x to the power of y, modulus z.

d. pop()

The pop() in python removes and returns the last value from the list or the given index value.

Difference Between List and Tuple in Python:

List Tuples
Lists are mutable Tuples are immutable
Implication of iterations is Time-consuming The implication of iterations is comparatively Faster
The list is better for performing operations, such as insertion and deletion. Tuple data type is appropriate for accessing the elements
Lists consume more memory Tuple consume less memory as compared to the list
Lists have several built-in methods Tuple does not have many built-in methods.
The unexpected changes and errors are more likely to occur In tuple, it is hard to take place.
  1. Lists and Tuples are ordered. They can be accessed by indexing
  2. Lists and Tuples can hold duplicate values.
  3. Lists and Tuples can hold mutable objects like lists.

Dictionary and list comprehensions are just another concise way to define dictionaries and lists.

Example of list comprehension is-

x = [i for i in range(5)]

The above code creates a list as below-

4
[0,1,2,3,4]

Example of dictionary comprehension is-

x = [i : i+2 for i in range(5)]

The above code creates a list as below-

[0: 2, 1: 3, 2: 4, 3: 5, 4: 6]

A literal in python source code represents a fixed value for primitive data types. There are 5 types of literals in python-

  1. String literals

A string literal is created by assigning some text enclosed in single or double quotes to a variable. To create multiline literals, assign the multiline text enclosed in triple quotes. Eg.name=”Tanya”

  1. Character literals

It is created by assigning a single character enclosed in double quotes. Eg. a=’t’

  1. Numeric literals

They include numeric values that can be either integer, floating point value, or a complex number. Eg. a=50

  1. Boolean literals

These can be 2 values- either True or False.

Literal Collections – These are of 4 types-

a) List collections-Eg.

a=[1,2,3,’Amit’]

b) Tuple literals- Eg.

a=(5,6,7,8)

c) Dictionary literals- Eg.

dict={1: ’apple’, 2: ’mango, 3: ’banana`’}

d) Set literals- Eg. {“Tanya”, “Rohit”, “Mohan”}

  1. Special literal- Python has 1 special literal None which is used to return a null variable.
# to create a database, you import sqlite3 from the library
import sqlite3
#next you create a connection to the database and store in a variable
#in the connect, directly parse the name of the database
con = sqlite3.connect ('customers.db')
#the database is automatically stored in the local computer

To run it locally on the computer:

  1. Open the command prompt on the computer
  2. change the directory to the directory of the database file. Assuming the directory for the database file is in the Users directory. cd /c/users/
  3. Then run it by putting python before creating the filename python database.py
  4. It has stored the python database in customers.db
#Create a cursor instance, it directs the database in creating tables
crs = con.cursor()
crs.execute ("""
                CREATE TABLE Customers (first_n TEXT, last_n TEXT, email TEXT,)
            """)
#commit and close the connection
con.commit()
con.close()

#run it at the commandline with python database.py

Insert Records into table:

import sqlite3
con = sqlite3.connect ('customers.db')
crs = con.cursor()
crs.execute (" INSERT INTO customers VALUES ('John', 'Elder', 'johne@gmail.com')")
con.commit()
con.close()

To Querry & Fetchall:

#to display we querry

import sqlite3
con = sqlite3.connect ('customers.db')
crs = con.cursor()
crs.execute (" SELECT * FROM customers")
crs.fetchall()
con.commit()
con.close()

print (crs.fetchall())

#run it through the command prompt

given_list = [5, 4, 3, 2, 1, -2, -3, -5]
total = 0
a= 0
while given_list [a] > 0:
    total += given_list[a]
    a+=1
print (total)

Output

15

A loop statement allows us to execute a statement or group of statements multiple times. Syntax:

for value in sequence:
    loop body

While loop is used to execute a block of statements repeatedly until a given a condition is satisfied. And when the condition becomes false, the line immediately after the loop in program is executed. Syntax :

while expression:
    statement(s)

A function is a collection of instructions. User-defined functions are codes or instructions that have been programmed and stored by the user for the purpose of calling it up. A user-defined function can also be used as a mapping. An example of a user-defined function:

def function1 ():
    print (“Lyrics one”)
    print (“Lyrics two”)
print (“This is outside the function”)
#to call up the function
print (function1 ())

OUTPUT:

Lyrics one
Lyrics two

A dictionary is a lookup table used to store data values in key:value pairs. Dictionaries are written with curly brackets, and have keys and values:

d = {key : value}

For example: Create and print a dictionary:

thisdict = {
  "brand": "Ford",
  "model": "Mustang",
  "year": 1964
}
print(thisdict)

OUTPUT:

{'brand': 'Ford', 'model': 'Mustang', 'year': 1964}

Slices are good for getting a subset of values in your list. For the example code below, it will return a list with the items from index 0 up to and not including index 2.

z= [3, 7, 4, 2]
index 0 1 2 3

First index is inclusive (before the :) and last (after the :) is not

# Define a list
z = [3, 7, 4, 2]
#slice to get between the 0th index and index before the 2nd
print(z[0:2])

OUTPUT:

[3, 7]

Enumerate() in Python is a built-in function used for assigning an index to each item of the iterable object. It adds a loop on the iterable objects while keeping track of the current item and returns the object in an enumerable form. This object can be used in a for loop to convert it into a list by using list() method.

Example of enumerate() is as follows:

Suppose we want to do numbering for our month ( Jan, Feb, Marc, ….June), so we declare the variable i that enumerate the numbers while m will print the number of month in list.

#use a for loop over a collection
Months = ["Jan","Feb","Mar","April","May","June"]
for i, m in enumerate (Months):
        print(i,m)
        
# use the break and continue statements
        
        #for x in range (10,20):
        #if (x == 15): break
        #if (x % 5 == 0) : continue
        #print x

n= 0
for a in range(1,100):
    if a%2 == 0:
        n += a
    elif a%4 == 0:
        n += a
print (n)

Output

2450

You can also copy the entire dictionary to a new dictionary. For example, here we have copied our original dictionary to the new dictionary name “Boys” and “Girls”.

Example

Dict = {'Tim': 18,'Charlie':12,'Tiffany':22,'Robert':25}    
Boys = {'Tim': 18,'Charlie':12,'Robert':25}
Girls = {'Tiffany':22}    
studentX=Boys.copy()
studentY=Girls.copy()
print(studentX)
print(studentY)