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Lectures 11: IO Operations

Course Leader: Jishmi Jos Choondal Department of Computer Science and Engineering Faculty of Engineering and Technology M. S. Ramaiah University of Applied Sciences

Objectives

• (^) At the end of this lecture, student will be able to
  • (^) Explain library functions and format used to perform input/output operations
  • (^) Use strings for the terminal input and output of text
  • (^) Construct a simple Python program that performs inputs, calculations, and outputs

Input From The User

• (^) Python has the input() built in function to display a prompt on screen, and then accept keyboard input, returning what was entered as a string to the code Note: Python takes all the input as a string input by default. To convert it to any other data type we have to convert the input explicitly.

  res = input('What is your favorite programming language: ') What is your favorite programming language: Python res Python res = input('What is your favorite programming language: ') print(res) What is your favorite programming language: Python Python

Reading a Numeric Value

• (^) Python takes all the input as a string input by default. To convert it to any other data type we have to convert the input explicitly.
• (^) For example, to convert the input to int or float we have to use the int() and float() method respectively.
• (^) When reading a numeric value from the user
  1. programmer must use the input() function to get the string of characters
  2. use the int or float syntax to construct the numeric value that character string represents

     year = int(input(“What is your age?” ))

Display on the Screen

Printing Multiple Items

• (^) To print multiple items, pass all the items in sequence separated by commas
• (^) They are automatically separated by commas print(“hello”,”world”) hello world print(“2+3=”,2+3) 2+3= 5 # there is a space after the = operator

Separating Items

• (^) To print multiple items but do not want space to be the separator, pass the separator string as an argument to print() print("hello","world",sep=',') hello,world print("hello","world",sep='<->') hello<->world print("welcome","to","python",sep='-') welcome-to-python

Terminating Items

• (^) By default, print() function prints a newline character ( \n ) after printing all the items
• (^) To control the termination of items, use the keyword end print("Is Python a dynamic language?",end="\nPython") Is Python a dynamic language? Python print("Is Python a dynamic language?\n",end="Python") Is Python a dynamic language? Python print("Is Python a dynamic language?\t",end="Python") Is Python a dynamic language? Python

Quotation Marks contd.

Double quotes

• (^) Any double quote character inside the string needs to be escaped by prefixing it with backslash
• (^) Example print(“Hello, World!”) print(“ ‘Hi’ from \”India\” “)
• (^) The output is Hello, World! ‘Hi’ from “India”

Formatting Strings Using format()

• (^) The format() function searches the string for placeholders
• (^) These placeholders are indicated by braces ( { } ) and indicate that some value needs to be substituted there
• (^) The format() takes any number of parameters
• (^) It is divided into two types of parameters:
  1. Positional parameters - list of parameters that can be accessed with index of parameter inside curly braces {index}
  2. Keyword parameters - list of parameters of type key=value, that can be accessed with key of parameter inside curly braces {key}

Keyword Arguments

• (^) Instead of just the parameters, a key-value for the parameters is used; name="Adam" and blc=230.

Formatting Strings - Examples

default arguments

print("Hello {}, your balance is {}.".format("Adam", 230.2346))

positional arguments

print("Hello {0}, your balance is {1}.".format("Adam", 230.2346)) #keyword arguments print("Hello {name}, your balance is {blc}.".format(name="Adam", blc=230.2346))

mixed arguments

print("Hello {0}, your balance is {blc}.".format("Adam", blc=230.2346))

• (^) All the above statements displays the same output Hello Adam, your balance is 230.2346.

Summary

• (^) The print() function prints a list of items
• (^) The input() function prints an optional prompt message and reads in a single line of input
• (^) Output formatting can be done using format() method of String class