Reading and writing data
Reading Data
In a Python program we use the predefined function input() to read data entered on the standard input stream (keyboard).
Example
name = input()
city = input()
When the interpreter encounters the input() function, it waits for the user to enter data on the standard input stream (keyboard) until the Enter key is pressed.
The entered character sequence can be stored in a variable of type str (string) for later use.
When the Enter key is read, the program moves to the next instruction.
To display a prompt message, it is passed as an argument to the input() function.
Example
name = input('Enter your name : ')
city = input('Enter your city : ')
Reading a Numeric Data
The type of a data read using the input() function is str (string).
To read a numeric data type, we use the predefined functions int(), float() to convert the data read using the input() function.
Example
width = int(input("Enter width : "))
height = int(input("Enter height : "))
print(width * height)
Writing Data
In a Python program we use the predefined function print() to write (display) data to the standard output stream (screen.)
Example
print('Hello World!')
The print() function accepts multiple arguments that are valid expressions.
Example
width = 7
height = 5
print('width : ', width)
print('height : ', height)
print('area : ', width * height)
The print() function emits a newline character ( \n ) at the end.
Consequently, the message displayed by the next print() statement appears on the next line of the console.
To display the results of two successive print() statements on the same line, we tell the print() function to emit a string as a separator at the end, and we do this by passing it as an argument named end.
Example
width = 7
height = 5
print('width : ', width, end=' ')
print('height : ', height, end=' ')
print('area : ', width * height)
The print() function displays its arguments separated by a space.
To use another character as a separator, we pass it as an argument named sep to the print() function.
Example: arguments separated by a comma.
width = 7
height = 5
area = width * height
print(width, height, area, sep=',')
Formatted Writing of Data
The str.format() method is used to format the display with the print() function.
The curly braces { } are used to specify the location and order of the arguments passed to the print() function.
Example
width = 7
height = 5
print('width : {} height : {}'.format(width, height))
f-Strings Format
The f-Strings format makes it easy to display values and variables.
Example
name = 'apple'
family = 'fruit'
print(f'{name} is a {family}')
Formatted Writing of Integers
Example: using the format() method.
i = 255
print('left : {:<8}'.format(i))
print('center : {:^8}'.format(i))
print('right : {:>8}'.format(i))
print('zero : {:08}'.format(i))
print('bin : {:b}'.format(i))
print('oct : {:o}'.format(i))
print('hex : {:x}'.format(i))
Executing these instructions displays the following messages:
left : 255
center : 255
right : 255
zero : 00000255
bin : 11111111
oct : 377
hex : ff
Example: using f-Strings format.
i = 255
print(f'left : {i:<8}')
print(f'center : {i:^8}')
print(f'right : {i:>8}')
print(f'zero : {i:08}')
print(f'bin : {i:b}')
print(f'oct : {i:o}')
print(f'hex : {i:x}')
Executing these instructions displays the following messages:
left : 255
center : 255
right : 255
zero : 00000255
bin : 11111111
oct : 377
hex : ff
Formatted Writing of Floats
Example: using the format() method.
r = 0.1234
print('digit : {:.2}'.format(r))
print('digit : {:.6f}'.format(r))
print('exp : {:.4e}'.format(r))
print('percent : {:.0%}'.format(r))
Executing these instructions displays the following messages:
digit : 0.12
digit : 0.123400
exp : 1.2340e-01
percent : 12%
Example: using f-Strings format.
r = 0.1234
print(f'digit : {r:.2}')
print(f'digit : {r:.6f}')
print(f'exp : {r:.4e}')
print(f'percent : {r:.0%}')
Executing these instructions displays the following messages:
digit : 0.12
digit : 0.123400
exp : 1.2340e-01
percent : 12%