Chapter 7 Console Input/Output

CHAPTER 7

Console Input/Output

Keynote

7.1 Console Input/Output

Console Input/Output means input from keyboard and output to screen.

7.2 Console Input

Console input can be received using the built-in input( ) function. General form of input( ) function is s = input('prompt') - prompt is a string that is displayed on the screen, soliciting a value. input( ) returns a string. If 123 is entered as input, '123' is returned.

# receive full name 
name = input('Enter full name') 
# separate first name, middle name and surname
fname, mname, lname = input('Enter full name: ').split( )

split( ) function will split the entered fullname with space as a delimiter. The split values will then be assigned to fname, mname, lname.

If we are to receive multiple int values, we can receive them as strings and then convert them to ints.

Receiving multiple int values

n1, n2, n3 = input('Enter three values: ').split( ) 
n1, n2, n3 = int(n1), int(n2), int(n3)
print(n1 + 10, n2 + 20, n3 + 30)

The same thing can be done using in a more compact manner using a feature called list comprehension. It applies int( ) function to every element of the list returned by the split( ) function.

List Comprehension

n1, n2, n3 = [int(n) for n in input('Enter three values: ').split( )] 
print(n1 + 10, n2 + 20, n3 + 30)

- The expression enclosed within [ ] is called list comprehension. It is discussed in detail in Chapter 12.

input( ) can be used to receive arbitrary number of values.

Receiving arbitrary number of values

numbers = [int(x) for x in input('Enter values: ').split( )] 
for n in numbers :
    print(n + 10)

input( ) can be used to receive different types of values at a time.

Receiving different types of values

data = input('Enter name, age, salary: ').split( ) 
name = data[0]
age = int(data[1])
salary = float(data[2])
print(name, age, salary)

7.3 Console Output

• Built-in function print( ) is used to send output to screen.

print( ) function has this form:

print(objects, sep = ' ', end = '\n', file = sys.stdout, flush = False)

• This means that by default objects will be printed on screen (sys.stdout), separated by space (sep = ' ') and last printed object will be followed by a newline (end = '\n'). flush = False indicates that output stream will not be flushed.

Python has a facility to call functions and pass keyword-based values as arguments. So while calling print( ) we can pass specific values for sep and end. In this case, default values will not be used; instead the values that we pass will be used.

Keyword-based arguments

print(a, b, c, sep = ',', end = '!') # prints ',' after each value, ! at end
print(x, y, sep = '...', end = '#') # prints '...' after each value, # at end

7.4 Formatted Printing

There are 4 ways to control the formatting of output:

• a. Using formatted string literals - easiest
• b. Using the format( ) method - older
• c. C printf( ) style - legacy
• d. Using slicing and concatenation operation - difficult

Today (a) is most dominantly used method followed by (b).

r, l, b = 1.5678, 10.5, 12.66
print(f'radius = {r}')
print(f'length = {l} breadth = {b} radius = {r}')

name = 'Sushant Ajay Raje'
for n in name.split( ) :
    print(f'{n:10}') # print in 10 columns

Using format( ) method of string object:

Using format( ) method

r, l, b = 1.5678, 10.5, 12.66
name, age, salary = 'Rakshita', 30, 53000.55

# print in order by position of variables using empty {}
print('radius = {} length = {} breadth ={}'.format(r, l, b))
print('name = {} age = {} salary = {}'.format(name, age, salary))

# print in any desired order
print('radius = {2} length = {1} breadth ={0}'.format(r, l, b))
print('age={1} salary={2} name={0}'.format(name, age, salary))

# print name in 15 columns, salary in 10 columns
print('name = {0:15} salary = {1:10}'.format(name, salary))

# print radius in 10 columns, with 2 digits after decimal point
print('radius = {0:10.2f}'.format(r))

• On execution, the above code snippet will produce the following output:

  radius = 1.5678 length = 10.5 breadth =12.66
  name = Rakshita age = 30 salary = 53000.55
  radius = 12.66 length = 10.5 breadth =1.5678
  age=30 salary=53000.55 name=Rakshita
  name = Rakshita salary = 53000.55
  radius = 1.57
  

Problems

Problem 7.1

Write a program to receive radius of a circle, and length and breadth of a rectangle in one call to input( ). Calculate and print the circumference of circle and perimeter of rectangle.

Program

r, l, b = input('Enter radius, length and breadth: ').split( ) 
radius = int(r)
length = int(l)
breadth = int(b)
circumference = 2 * 3.14 * radius 
perimeter = 2 * ( length + breadth ) 
print(circumference)
print(perimeter)

Output

Enter radius, length and breadth: 3 4 5
18.84
18

Tips

• input( ) returns a string, so it is necessary to convert it into int or float suitably, before performing arithmetic operations.

Problem 7.2

Write a program to receive 3 integers using one call to input( ). The three integers signify starting value, ending value and step value for a range. The program should use these values to print the number, its square and its cube, all properly right-aligned. Also output the same values left-aligned.

Program

start, end, step = input('Enter start, end, step values: ').split( )
# right aligned printing
for n in range(int(start), int(end), int(step)) :
print(f'{n:>5}{n**2:>7}{n**3:>8}')
print( ) 

# left aligned printing
for n in range(int(start), int(end), int(step)) :
print('{0:<5}{1:<7}{2:<8}'.format(n, n ** 2, n ** 3))

Output

Enter start, end, step values: 1 10 2
1 1 1
3 9 27
5 25 125
7 49 343
9 81 729

1 1 1 
3 9 27 
5 25 125 
7 49 343 
9 81 729 

Tips

• {n:>5} will print n right-justified within 5 columns. Use < to left-justify.
• {0:<5} will left-justify 0^th parameter in the list within 5 columns. Use > to right-justify.

Problem 7.3

Write a program to maintain names and cell numbers of 4 persons and then print them systematically in a tabular form.

Program

contacts = {

'David' : 9823077892, 'Shine' : 6784512345,
'Vivad' : 9823011245, 'Rosanna' : 9766556779 

}
for name, cellno in contacts.items( ) :
print(f'{name:15} : {cellno:10d}')

Output

David : 9823077892
Shine : 6784512345
Vivad : 9823011245
Rosanna : 9766556779

Problem 7.4

Suppose there are 5 variables in a program—max, min, mean, sd and var, having some suitable values. Write a program to print these variables properly aligned using multiple fstrings, but one call to print( ).

Program

min, max = 25, 75
mean = 35
sd = 0.56
var = 0.9
print(
    f'\n{"Max Value:":<15}{max:>10}',
    f'\n{"Min Value:":<15}{min:>10}',
    f'\n{"Mean:":<15}{mean:>10}',
    f'\n{"Std Dev:":<15}{sd:>10}',
    f'\n{"Variance:":<15}{var:>10}' )

Output

Max Value: 75 
Min Value: 25 
Mean: 35 
Std Deviation: 0.56 
Variance: 0.9

Problem 7.5

Write a program that prints square root and cube root of numbers from 1 to 10, up to 3 decimal places. Ensure that the output is displayed in separate lines, with number center-justified and square and cube roots, right-justified.

Program

import math
width = 10
precision = 4
for n in range(1, 10) :
s = math.sqrt(n)
c = math.pow(n,1/3)
print(f'{n:^5}{s:{width}.{precision}}{c:{width}.{precision}}')

Output

1 1.0 1.0
2 1.414 1.26
3 1.732 1.442
4 2.0 1.587
5 2.236 1.71
6 2.449 1.817
7 2.646 1.913
8 2.828 2.0
9 3.0 2.08

Exercises

[A] Attempt the following questions:

a. How will you make the following code more compact?

print('Enter ages of 3 persons')
age1 = input( )
age2 = input( )
age3 = input( )

b. How will you print "Rendezvous" in a line and retain the cursor in the same line in which the output has been printed?

c. What will be the output of the following code snippet?

l, b = 1.5678, 10.5
print('length = {l} breadth = {b}')

d. In the following statement what do > 5, > 7 and > 8 signify?

print(f'{n:>5}{n ** 2:>7}{n ** 3:>8}')

e. What will be the output of the following code segment?

name = 'Shine'
cellno = 9823017892
print(f'{name:15} : {cellno:10}')

f. How will you print the output of the following code segment using fstring?

x, y, z =10, 20, 40
print('{0:<5}{1:<7}{2:<8}'.format(x, y, z))

g. How will you receive arbitrary number of floats from keyboard?

h. What changes should be made in

print(f'{'\nx = ':4}{x:>10}{'\ny = ':4}{y:>10}')
to produce the output given below:
x = 14.99 
y = 114.39 

i. How will you receive a boolean value as input?

j. How will you receive a complex number as input?

k. How will you display price in 10 columns with 4 places beyond decimal points? Assume value of price to be 1.5567894.

l. Write a program to receive an arbitrary number of floats using one input( ) statement. Calculate the average of floats received.

m. Write a program to receive the following using one input( ) statement.

Name of the person
Years of service
Diwali bonus received
Calculate and print the agreement deduction as per the following 
formula:
deduction = 2 * years of service + bonus * 5.5 / 100

n. Which import statement should be added to use the built-in functions input( ) and print( )?

o. Is the following statement correct?

print('Result = ' + 4 > 3)

p. Write a program to print the following values

a = 12.34, b = 234.39, c = 444.34, d = 1.23, e = 34.67

as shown below:

a = 12.34 
b = 234.39 
c = 444.34 
d = 1.23 
e = 34.67

[B] Match the following pairs:

Option A	Option B
a. Default value of sep in print( )	1. ' '
b. Default value of end in print( )	2. Using fstring
c. Easiest way to print output	3. Right justify num in 5 columns
d. Return type of split( )	4. Left justify num in 5 columns
e. print('{num:>5}')	5. list
f. print('{num:<5}')	6. \n

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