Packages in Python Programming

19/04/2018 Suryateja Pericherla Categories: Python Programming. No Comments

Contents

1 Introduction
2 Creating a Package
3 PyPI and Pip
4 Standard Library Modules
5 globals(), locals(), and reload()

Introduction

A package is a directory structure which can contain modules and sub packages. Every package in Python is a directory which must contain a special file called __init.py__. The file __init.py__ can be empty. To allow only certain modules to be imported, we can use the __all__ variable in __init.py__ file as follows:

__all__ = [“Stat”]

1	__all__ = [“Stat”]

The above line says that only Stat module in the package can be imported.

Every package must be a folder in the system. Packages should be placed in the path which is pointed by sys.path. If the package is not available, then ImportError is raised.

Creating a Package

A package (folder) named CustomMath is created with an empty __init__.py file inside it. In the package CustomMath, a single module named BasicMath is created which contains three functions as follows:

def prod(x, y):
	return x*y 

def rem(x, y):
	return x%y 


def lastdigit(x):
	return x%10

def prod(x, y):

return x*y

def rem(x, y):

return x%y

def lastdigit(x):

return x%10

A new Python script is written which uses our custom package named CustomMath as follows:

from  CustomMath.BasicMath  import  *
print(prod(4,3))
print(rem(4,3))
print(lastdigit(99))

from CustomMath.BasicMath import *

print(prod(4,3))

print(rem(4,3))

print(lastdigit(99))

PyPI and Pip

Third party packages are available in Python Package Index (PyPI). We can import the modules available in the third party packages by using the pip tool. Pip is a command line tool for maintaing Python packages.

To install a package using pip we write:

pip  install  package-name

1	pip install package-name

To see the list of existing packages, we write:

pip list

pip list

Standard Library Modules

Python comes with several built-in modules. We can use them when necessary. These built-in modules forms the Python’s standard library. Some of the modules in standard library are:

string
re
datetime
math
random
os
multiprocessing
subprocess
email
json
doctest
unittest
pdb
argparse
socket
sys

globals(), locals(), and reload()

The globals() function returns all the names in the global namespace that can be accessed from inside a function.

The locals() function returns all the names in the local namespace i.e., within the function. Both the above functions returns the names as a dictionary.

The reload() function can be used to reload a module again the program if need as follows:

reload(module_name)

1	reload(module_name)