Packages

Packages

• Packages are namespaces which contain multiple packages and modules. They are simply directories.

• Along with packages and modules the package contains a file named __init_ _.py. In fact to be a package, there must be a file called __init_ _.py in the folder.

• Packages can be nested to any depth, provided that the corresponding directories contain their own _init__.py file.

•  The arrangement of packages is as shown in Fig. 5.5.1.

Fig. 5.5.1

For example :

We can access the package and various subpackages and modules in it as follows:

import My_Package #loads My_Package/ _init__.py

import My_Package.module1 #loads My_Package/module1.py

from My_Package import module2

import My_Package.SubPackage1

When we import Main package then there is no need to import subpackage. For example

import My_Package My_Package.

SubPackage1.my_function1( )

• Thus we need not have to import SubPackage1.

• The primary use of __init__.py is to initialize Python packages. Simply putting the subdirectories and modules inside a directory does not make a directory a package, what it needs is a __init_.py inside it. Then only Python treats that directory as package.

How to Create a Package ?

• To understand how to create a package, let us take an example. We will perform arithmetic operations addition, multiplication, division and subtraction operations by creating a package. Just follow the given steps to create a package.

Step 1: Create a folder named MyMaths in your working drive. I have created it on D:drive.

Step 2: Inside MyMaths directory create _init_.py file. Just create an empty file.

Step 3: Create a folder named Add inside MyMaths. Inside Add folder create file named addition.py. The addition.py will be as follows

addition.py

def add_fun(a,b):

return a + b

Step 4: Similarly the folder Sub insider MyMaths is created. Inside which create a file subtraction.py. The code for this file is

subtraction.py

def sub_fun(a,b):

return(a-b)

Step 5: Similarly the folder Mul insider MyMaths is created. Inside which create a file multiplication.py. The code for this file is

multiplication.py

def mul_fun(a,b):

return(a*b)

Step 6: Similarly the folder Div insider MyMaths is created. Inside which create a file division.py. The code for this file is

division.py

def div_fun(a,b):

return (a/b)

Step 7: The overall directory Structure will be as given below. Note that _pycache_is automatically generated directory.

Step 8: Now on the D: drive create a driver program which will invoke all the above functionalities present in the MyMaths package. I have named this driver program as testing_arithmetic.py. It is as follows

print("The addition of 10 and 20 is: ",MyMaths.Add.addition.add_fun(10,20))

print("The multiplication of 10 and 20 is: ",MyMaths.Mul.multiplication.mul_fun(10,20))

print("The division of 10 and 5 is: ",MyMaths.Div.division.div_fun(10,5))

print("The subtraction of 20 and 10 is: ",MyMaths.Sub.subtraction.sub_fun(20,10))

Step 9: Now just run this testing program and you will get following output

Output

The addition of 10 and 20 is:30

The multiplication of 10 and 20 is:200

 Illustrative Programs

 

1. Word Count

This program counts the number of words present in the given file. If the specified file is not present, then exception is raised.

Step 1:

Python Program

try:

inFile = open("D:\\test.txt",'rt')

except:

print("Error: File not found")

else:

data inFile.read()

words = data.split()

print(words)

print('-'*80)

print("Total number of words are ",len(words))

print('-'*80)

Step 2:

The input file used for reading and for word counting is as follows

Step 3:

The output for the Python program created in Step 1 is as follows –

 

2. Copy File

In this program, the contents of one file are copied line by line to another file. For that purpose I have created a file named one.txt in which some contents are stored. These contents are copied to another file named two.txt. The python program for this is as given below -

Step 1: The python program is as follows –

print("\t Program for Copying the File")

with open("d:\\one.txt") as inFile:

with open("d:\\two.txt","w") as outFile:

for line in inFile:

outFile.write(line)

inFile.close()

outFile.close()

print("The contents of original File are... \n")

with open("D:\\one.txt") as inFile:

print(inFile.read()).

inFile.close()

print("\nThe contents of copied File are... \n")

with open("D:\\two.txt") as in File:

print(inFile.read())

inFile.close()

Step 2: The input file one.txt is as follows –

one.txt

Step 3: The output of the python program created in step 1 is as follows -

3. Voter's Age Validation

Python Program

try:

age = int(input("Enter your age: "))

if age > 18:

print("Eligible to vote!!!")

else:

print("Not eligible to vote!!!")

except ValueError as err:

print(err)

finally:

# code to be executed whether exception occurs or not

#typically for closing files and other resources

print("Good Bye!!!")

Output(Run 1)

Enter your age: 20

Eligible to vote!!!

Good Bye!!!

>>> 

Output(Run 2)

Enter your age: twenty

invalid literal for int() with base 10: 'twenty'

Good Bye!!!

>>> 

 

4. Marks Range Validation (0-100)

Python Program

while True :

try:

num = int(input("Enter a number between 1 and 100: "))

if num in range(1,100):

print("Valid number!!!")

break

else :

print("Invalid number. Try again.")

except :

print("That is not a number. Try again.")

Output

Enter a number between 1 and 100: -1

Invalid number. Try again.

Enter a number between 1 and 100-10000

Invalid number. Try again.

Enter a number between 1 and 100- five

This not a number . Try again

Enter a number between 1 and 100: 99

Valid number

>>> 

Review Question

1. Design a Python code to count the number of words in a Python file.

AU : May-19,Dec.-19, Marks 8