Unit2 input output

Python provides numerous built-in functions that are
readily available to us at the Python prompt.
Some of the functions like input() and print() are
widely used for standard input and output operations
respectively
Python Input and Output

Python Input
• In Python, we have the input() function to allow to take the input
from the user. The syntax for input() is
input([prompt])
where prompt is the string we wish to display on the screen. It is
optional.
>>> num = input('Enter a number: ')
Enter a number: 10
>>> num
'10'
Here, we can see that the entered value 10 is a string, not a number. To
convert this into a number we can use int() or float() functions.
>>> int('10')
10
>>> float('10')
10.0

• This same operation can be performed using the eval() function. But
it takes it further. It can evaluate even expressions, provided the input
is a string
>>> int('2+3')
Traceback (most recent call last):
File "<string>", line 301, in runcode
File "<interactive input>", line 1, in <module>
ValueError: invalid literal for int() with base 10: '2+3'
>>> eval('2+3')
5

Python Output Using print() function
The print() function to output data to the standard output device
(screen).
• We can also output data to a file, but this will be discussed later. An
example use is given below.
print('This sentence is output to the screen')
# Output: This sentence is output to the screen
a = 5
print('The value of a is', a)
# Output: The value of a is 5

• In the second print() statement, we can notice that a space was
added between the string and the value of variable a. This is by
default, but we can change it.
• The actual syntax of the print() function is
print(*objects, sep=' ', end='n', file=sys.stdout, flush=False)
• Here,
• The sep separator is used between the values. It defaults into a space
character.
• After all values are printed, end is printed. It defaults into a new line.
objects is the value(s) to be printed.
• The file is the object where the values are printed and its default
value is sys.stdout (screen).

Here are an example to illustrate this
print(1,2,3,4)
# Output: 1 2 3 4
print(1,2,3,4,sep='*')
# Output: 1*2*3*4
print(1,2,3,4,sep='#',end='&')
# Output: 1#2#3#4&

Output formatting
• Sometimes we would like to format our output to make it look
attractive. This can be done by using the str.format() method. This
method is visible to any string object.
>>> x = 5; y = 10
>>> print('The value of x is {} and y is {}'.format(x,y))
The value of x is 5 and y is 10
• Here the curly braces {} are used as placeholders. We can specify the
order in which it is printed by using numbers (tuple index).
print('I love {0} and {1}'.format('bread','butter'))
# Output: I love bread and butter
print('I love {1} and {0}'.format('bread','butter'))
# Output: I love butter and bread

• We can even use keyword arguments to format the string.
>>> print('Hello {name}, {greeting}'.format(greeting = 'Goodmorning', name =
'John'))
Hello John, Goodmorning
We can even format strings like the old sprintf() style used in C
programming language. We use the % operator to accomplish this.
>>> x = 12.3456789
>>> print('The value of x is %3.2f' %x)
The value of x is 12.35
>>> print('The value of x is %3.4f' %x)
The value of x is 12.3457

Python Import
• When our program grows bigger, it is a good idea to break it into
different modules.
• A module is a file containing Python definitions and statements.
Python modules have a filename and end with the extension .py.
• Definitions inside a module can be imported to another module or
the interactive interpreter in Python. We use the import keyword to
do this.
• For example, we can import the math module by typing in import
math.
import math
print(math.pi)

• Now all the definitions inside math module are available in our scope. We can also
import some specific attributes and functions only, using the from keyword. For example:
>>> from math import pi
>>> pi
3.141592653589793
While importing a module, Python looks at several places defined in sys.path. It is a list of
directory locations.
>>> import sys
>>> sys.path
['', 'C:UsersDeepakAppDataLocalProgramsPythonPython37-32Libidlelib',
'C:UsersDeepakAppDataLocalProgramsPythonPython37-32python37.zip',
'C:UsersDeepakAppDataLocalProgramsPythonPython37-32DLLs',
'C:UsersDeepakAppDataLocalProgramsPythonPython37-32lib',
'C:UsersDeepakAppDataLocalProgramsPythonPython37-32',
'C:UsersDeepakAppDataLocalProgramsPythonPython37-32libsite-packages']

Unit2 input output

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Unit2 input output