All the IPython Notebooks in Python Introduction lecture series by Dr. Milaan Parmar are available @ GitHub
This class focuses on two built-in functions print() and input() to perform I/O task in Python. Also, you will learn to import modules and use them in your program.
Python provides numerous built-in functions that are readily available to us at the Python prompt.
Some of the functions like print() and input() are widely used for standard input and output operations respectively. Let us see the output section first.
print() function¶We use 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 of its use is given below.
# Example 1:
print('This sentence is output to the screen')
This sentence is output to the screen
# Example 2:
a = 9
print('The value of a is', a)
The value of a is 9
In the second print() statement, we can notice that space was added between the string and the value of variable a. This is by default, but we can change it.
Syntax of the print() function is:
print(*objects, sep=' ', end='\n', file=sys.stdout, flush=False)
Here, objects is the value(s) to be printed.
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.
The file is the object where the values are printed and its default value is sys.stdout (screen). Here is an example to illustrate this.
print(1, 2, 3, 4)
print(1, 2, 3, 4, sep='#') # It will separate your elements with '#'
print(1, 2, 3, 4, sep='*', end='&') # It will separate your elements with '*' and end with '&'
1 2 3 4 1#2#3#4 1*2*3*4&
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 = 6; y = 12
print('The value of x is {} and y is {}'.format(x,y))
The value of x is 6 and y is 12
Here, the curly braces {} are used as placeholders. We can specify the order in which they are printed by using numbers (tuple index).
print('I love {0} and {1}'.format('Mango','Banana'))
print('I love {1} and {0}'.format('Mango','Banana'))
I love Mango and Banana I love Banana and Mango
We can even use keyword arguments to format the string.
print('Hello {name}, {greeting}!'.format(greeting = 'Good morning', name = 'Mark'))
Hello Mark, Good morning!
We can also format strings like the old sprintf() style used in C programming language. We use the % operator to accomplish this.
x = 12.34567890
print('The value of x is %0.2f' %x) # "%0.2" means only 2 number after decimal
print('The value of x is %0.3f' %x) # "%0.3" means only 3 number after decimal
The value of x is 12.35 The value of x is 12.346
input() function¶Up until now, our programs were static. The value of variables was defined or hard coded into the source code.
To allow flexibility, we might want to take the input from the user. In Python, we have a built-in function input() to accept user input.
Syntax:
input([prompt])
where prompt is the string we wish to display on the screen. It is optional.
num = input('Enter a number: ')
num
Enter a number: 90
'90'
Here, we can see that the entered value 90 is a string, not a number. To convert this into a number we can use int() or float() functions.
int('90') # converting string '90' to integer
90
float('90')
90.0
a = "6" # Is this a STRING character
b = "P" # IS this a STRING chracter
c = a + b
print(c)
6P
int('6+3') # ERROR! cannot add numbers as string data type
--------------------------------------------------------------------------- ValueError Traceback (most recent call last) <ipython-input-12-b4c816180ad9> in <module> ----> 1 int('6+3') # ERROR! cannot add numbers as string data type ValueError: invalid literal for int() with base 10: '6+3'
This same operation can be performed using the eval() function. But eval takes it further. It can evaluate even expressions, provided the input is a string.
eval('6+3') # Eval function can add numbers in string data type
9
eval('3*6')
18
input(prompt) prompts for and returns input as a string. Hence, if the user inputs a integer, the code should convert the string to an integer and then proceed.
a = input("Hello, \nHow are you?") # \n means new line
Hello, How are you?I'm fine, thanks and you?
abc = input("Type something here and it will be stored in variable abc \t")
Type something here and it will be stored in variable abc 999999
type(abc)
str
Note: type( ) returns the format or the type of a variable or a number
name = input("Enter Student Name: ")
major = input("Enter Major: ")
university = input("Enter University: ")
print("\n")
print("Printing Student Details")
print("Name", "Major", "University")
print(name, major, university)
Enter Student Name: Arthur Enter Major: IT Enter University: Oxford Printing Student Details Name Major University Arthur IT Oxford
number = input("Enter number: ")
name = input("Enter name: ")
print("\n")
print("Printing type of a input value")
print("type of number", type(number))
print("type of name", type(name))
Enter number: 007 Enter name: Bond Printing type of a input value type of number <class 'str'> type of name <class 'str'>
A useful function to use in conjunction with this is eval() which takes a string and evaluates it as a python expression.
Note: In notebooks it is often easier just to modify the code than to prompt for input.
xyz = input("xyz = ")
print(xyz)
print(type(xyz))
xyzValue=eval(xyz) # change input to integer data type from string data type
print(xyz,'=',xyzValue)
xyz = 66 66 <class 'str'> 66 = 66
int("99")
99
# program to calculate addition of two input numbers
first_number = int(input("Enter first number: ")) # converting input value to integer
second_number = int(input("Enter second number: ")) # converting input value to integer
print("\n")
print("First Number: ", first_number)
print("Second Number: ", second_number)
sum1 = first_number + second_number
print("Addition of two number is: ", sum1)
Enter first number: 3 Enter second number: 6 First Number: 3 Second Number: 6 Addition of two number is: 9
Accept one integer and one float number from the user and calculate the addition of both the numbers.
num1 = int(input("Enter first number: "))
num2 = float(input("Enter second number: "))
result=(num1+num2)
print("Final result is: ", result)
Enter first number: 6 Enter second number: 3.9 Final result is: 9.9
# Write code to get three numbers and add first 2 number and multiply with third number
num1 = int(input("Enter first number: ")) # converting input value to integer
num2 = int(input("Enter second number: ")) # converting input value to integer
num3 = int(input("Enter third number: ")) # converting input value to integer
print("\n")
print("First Number: ", num1)
print("Second Number: ", num2)
print("Third Number: ", num3)
result=(num1+num2)*num3
print("Final result is: ", result)
Enter first number: 1 Enter second number: 2 Enter third number: 3 First Number: 1 Second Number: 2 Third Number: 3 Final result is: 9
# Write a code to get four numbers:
#Step 1. Multiply first and fourth number
#Step 2. Divide second and third number
#Step3. Add Step 1 and Step 2 outputs.
num1 = int(input("Enter first number: "))
num2 = int(input("Enter second number: "))
num3 = int(input("Enter third number: "))
num4 = int(input("Enter fourth number: "))
print("\n")
print("First Number: ", num1)
print("Second Number: ", num2)
print("Third Number: ", num3)
print("Fourth number: ", num4)
result=(num1*num4)+(num2/num3)
print("Final result is: ", result)
Enter first number: 5 Enter second number: 6 Enter third number: 7 Enter fourth number: 8 First Number: 5 Second Number: 6 Third Number: 7 Fourth number: 8 Final result is: 40.857142857142854
# Write a code to get cube of the number
def cube(x):
return x*x*x
a=int(input("Enter number: "))
print("cube of",a,"is",cube(a))
Enter number: 3 cube of 3 is 27
Let’s see how to accept float value from a user in Python. You need to convert user input to the float number using the float() function as we did for the integer value.
float_number = float(input("Enter float number: ")) # converting input value to float
print("\n")
print("input float number is: ", float_number)
print("type is:", type(float_number))
Enter float number: 9 input float number is: 9.0 type is: <class 'float'>
In Python, It is possible to get multiple values from the user in one line. i.e., In Python, we can accept two or three values from the user in one input() call.
For example, in a single execution of the input() function, we can ask the user his/her name, age, and phone number and store it in three different variables. Lets see how to do this.
name, age, phone = input("Enter your Name, Age, Phone_number separated by space: ").split()
print("\n")
print("User Details: ", name, age, phone)
Enter your Name, Age, Phone_number separated by space: Clark 36 13756537093 User Details: Clark 36 13756537093
As you know, the input() function does not allow the user to enter put lines separated by a newline. If the user tries to enter multiline input, it prints back only the first line. Let’s see how to gets multiple line input.
As you know, the input() function does not allow the user to enter put lines separated by a newline. If the user tries to enter multiline input, it prints back only the first line. Let’s see how to gets multiple line input.
We can use for loop. In each iteration, we can get input string from the user and then .join() them using \n, or you can also concatenate each input string using + operator separated by \n.
MultiLine = []
print("Tell me about yourself")
while True:
line = input()
if line:
MultiLine.append(line)
else:
break
finalText = '\n'.join(MultiLine)
print("\n")
print("Final text input")
print(finalText)
Tell me about yourself Hello! I am happy to learn Python and I love travelling. Also, I love cooking and singing. Final text input Hello! I am happy to learn Python and I love travelling. Also, I love cooking and singing.
firstName = input("Enter First Name: ")
lastName = input("Enter Last Name: ")
organization = input("Enter Organization Name: ")
print("\n")
print('{0}, {1} works at {2}'.format(firstName, lastName, organization))
print('{1}, {0} works at {2}'.format(firstName, lastName, organization))
print('FirstName {0}, LastName {1} works at {2}'.format(firstName, lastName, organization))
print('{0}, {1} {0}, {1} works at {2}'.format(firstName, lastName, organization))
Enter First Name: Ethan Enter Last Name: Hunt Enter Organization Name: Mission Impossible Ethan, Hunt works at Mission Impossible Hunt, Ethan works at Mission Impossible FirstName Ethan, LastName Hunt works at Mission Impossible Ethan, Hunt Ethan, Hunt works at Mission Impossible
name = input("Enter Name: ")
marks = input("Enter marks: ")
print("\n")
print('Student: Name: {firstName}, Marks: {percentage}%'.format(firstName=name, percentage=marks))
Enter Name: David Enter marks: 85 Student: Name: David, Marks: 85%
text = input("Enter text: ")
print("\n")
# left aligned
print('{:<25}'.format(text)) # Right aligned print('{:>25}'.format(text))
# centered
print('{:^25}'.format(text))
# right aligned
print('{:>25}'.format(text))
Enter text: Python
Python
Python
Python
positive_number = float(input("Enter Positive Number: "))
negative_number = float(input("Enter Negative Number: "))
print("\n")
# sign '+' is for both positive and negative number
print('{:+f}; {:+f}'.format(positive_number, negative_number))
# sign '-' is only for negative number
print('{:f}; {:-f}'.format(positive_number, negative_number))
Enter Positive Number: 9 Enter Negative Number: -4 +9.000000; -4.000000 9.000000; -4.000000
number = int(input("Enter number: "))
print("\n")
# 'd' is for integer number formatting
print("The number is:{:d}".format(number))
# 'o' is for octal number formatting, binary and hexadecimal format
print('Output number in octal format : {0:o}'.format(number))
# 'b' is for binary number formatting
print('Output number in binary format: {0:b}'.format(number))
# 'x' is for hexadecimal format
print('Output number in hexadecimal format: {0:x}'.format(number))
Enter number: 63 The number is:63 Output number in octal format : 77 Output number in binary format: 111111 Output number in hexadecimal format: 3f
number = float(input("Enter float Number: "))
print("\n")
# 'f' is for float number arguments
print("Output Number in The float type :{:f}".format(number))
# padding for float numbers
print('padding for output float number{:5.2f}'.format(number))
# 'e' is for Exponent notation
print('Output Exponent notation{:e}'.format(number))
# 'E' is for Exponent notation in UPPER CASE
print('Output Exponent notation{:E}'.format(number))
Enter float Number: 33 Output Number in The float type :33.000000 padding for output float number33.00 Output Exponent notation3.300000e+01 Output Exponent notation3.300000E+01
Let’s see how to use str.rjust(), str.ljust() and str.center() to justify text output on screen and console.
text = input("Enter String: ")
print("\n")
print("Left justification", text.ljust(60, "*"))
print("Right justification", text.rjust(60, "*"))
print("Center justification", text.center(60, "*"))
Enter String: Jupyter Left justification Jupyter***************************************************** Right justification *****************************************************Jupyter Center justification **************************Jupyter***************************
Import function¶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 the following line:
>import math
We can use the module in the following ways:
import math
print(math.pi) # do not have to make vairable for pi
3.141592653589793
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:\\Users\\Deepak\\01_Learn_Python4Data\\01_Python_Introduction', 'C:\\ProgramData\\Anaconda3\\python38.zip', 'C:\\ProgramData\\Anaconda3\\DLLs', 'C:\\ProgramData\\Anaconda3\\lib', 'C:\\ProgramData\\Anaconda3', '', 'C:\\Users\\Deepak\\AppData\\Roaming\\Python\\Python38\\site-packages', 'C:\\ProgramData\\Anaconda3\\lib\\site-packages', 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\locket-0.2.1-py3.8.egg', 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\win32', 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\win32\\lib', 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\Pythonwin', 'C:\\ProgramData\\Anaconda3\\lib\\site-packages\\IPython\\extensions', 'C:\\Users\\Deepak\\.ipython']
We can also add our own location to this list.