Python - Modules

Python Modules

The concept ofmodulein Python further enhances the modularity. You can define more than one related functions together and load required functions. A module is a file containing definition of functions,classes,variables, constants or any other Python object. Contents of this file can be made available to any other program. Python has theimportkeyword for this purpose.

Afunctionis a block of organized, reusable code that is used to perform a single, related action. Functions provide better modularity for your application and a high degree of code reusing.

Example of Python Module

PYTHON CODE

import math
print ("Square root of 100:", math.sqrt(100))

It will produce the followingoutput−

PYTHON CODE

Square root of 100: 10.0

Python Built-in Modules

Python’s standard library comes bundled with a large number of modules. They are called built-in modules. Most of these built-in modules are written in C (as the reference implementation of Python is in C), and pre-compiled into the library. These modules pack useful functionality like system-specific OS management, disk IO, networking, etc.

Here is a select list of built-in modules −

Sr.No.	Name & Brief Description
1	osThis module provides a unified interface to a number of operating system functions.
2	stringThis module contains a number of functions for string processing
3	reThis module provides a set of powerful regular expression facilities. Regular expression (RegEx), allows powerful string search and matching for a pattern in a string
4	mathThis module implements a number of mathematical operations for floating point numbers. These functions are generally thin wrappers around the platform C library functions.
5	cmathThis module contains a number of mathematical operations for complex numbers.
6	datetimeThis module provides functions to deal with dates and the time within a day. It wraps the C runtime library.
7	gcThis module provides an interface to the built-in garbage collector.
8	asyncioThis module defines functionality required for asynchronous processing
9	CollectionsThis module provides advanced Container datatypes.
10	functoolsThis module has Higher-order functions and operations on callable objects. Useful in functional programming
11	operatorFunctions corresponding to the standard operators.
12	pickleConvert Python objects to streams of bytes and back.
13	socketLow-level networking interface.
14	sqlite3A DB-API 2.0 implementation using SQLite 3.x.
15	statisticsMathematical statistics functions
16	typingSupport for type hints
17	venvCreation of virtual environments.
18	jsonEncode and decode the JSON format.
19	wsgirefWSGI Utilities and Reference Implementation.
20	unittestUnit testing framework for Python.
21	randomGenerate pseudo-random numbers
22	sysProvides functions that acts strongly with the interpreter.
23	requestsIt simplifies HTTP requests by offering a user-friendly interface for sending and handling responses.
24	itertoolsAn iterator object is used to traverse through a collection (i.e., list, tuple etc..). This module provides various tools which are used to create and manipulate iterators.
25	localeThelocalemodule in Python is used to set and manage cultural conventions for formatting data. It allows programmers to adapt their programs to different languages and regional formatting standards by changing how numbers, dates, and currencies are displayed.

Python User-defined Modules

Any text file with.pyextension and containing Python code is basically a module. It can contain definitions of one or more functions, variables, constants as well as classes. Any Python object from a module can be made available to interpreter session or another Python script by import statement. A module can also include runnable code.

Creating a Python Module

Creating a module is nothing but saving a Python code with the help of any editor. Let us save the following code asmymodule.py

PYTHON CODE

def SayHello(name):
   print ("Hi {}! How are you?".format(name))
   return

You can now import mymodule in the current Python terminal.

PYTHON CODE

&gt;&gt;&gt; import mymodule
&gt;&gt;&gt; mymodule.SayHello("Harish")
Hi Harish! How are you?

You can also import one module in another Python script. Save the following code as example.py

PYTHON CODE

import mymodule
mymodule.SayHello("Harish")

Run this script from command terminal

PYTHON CODE

Hi Harish! How are you?

The import Statement

In Python, theimportkeyword has been provided to load a Python object from one module. The object may be a function, class, a variable etc. If a module contains multiple definitions, all of them will be loaded in the namespace.

Let us save the following code having three functions asmymodule.py.

PYTHON CODE

def sum(x,y):
   return x+y

def average(x,y):
   return (x+y)/2

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

Theimport mymodulestatement loads all the functions in this module in the current namespace. Each function in the imported module is an attribute of this module object.

PYTHON CODE

&gt;&gt;&gt; dir(mymodule)
['__builtins__', '__cached__', '__doc__', '__file__', '__loader__', '__name__', '__package__', '__spec__', 'average', 'power', 'sum']

To call any function, use the module object’s reference. For example, mymodule.sum().

PYTHON CODE

import mymodule
print ("sum:",mymodule.sum(10,20))
print ("average:",mymodule.average(10,20))
print ("power:",mymodule.power(10, 2))

It will produce the followingoutput−

PYTHON CODE

sum:30
average:15.0
power:100

The from … import Statement

The import statement will load all the resources of the module in the current namespace. It is possible to import specific objects from a module by using this syntax. For example −

Out of three functions inmymodule, only two are imported in following executable scriptexample.py

PYTHON CODE

from mymodule import sum, average
print ("sum:",sum(10,20))
print ("average:",average(10,20))

It will produce the following output −

PYTHON CODE

sum: 30
average: 15.0

Note that function need not be called by prefixing name of its module to it.

The from…import * Statement

It is also possible to import all the names from a module into the current namespace by using the following import statement −

PYTHON CODE

from modname import *

This provides an easy way to import all the items from a module into the current namespace; however, this statement should be used sparingly.

The import … as Statement

You can assign an alias name to the imported module.

PYTHON CODE

from modulename as alias

Thealiasshould be prefixed to the function while calling.

Take a look at the followingexample−

PYTHON CODE

import mymodule as x
print ("sum:",x.sum(10,20))
print ("average:", x.average(10,20))
print ("power:", x.power(10, 2))

Locating Modules

When you import a module, the Python interpreter searches for the module in the following sequences −

The current directory.
If the module isn’t found, Python then searches each directory in the shell variable PYTHONPATH.
If all else fails, Python checks the default path. On UNIX, this default path is normally /usr/local/lib/python/.

The module search path is stored in the system module sys as thesys.pathvariable. The sys.path variable contains the current directory, PYTHONPATH, and the installation-dependent default.

ThePYTHONPATHVariable

The PYTHONPATH is an environment variable, consisting of a list of directories. The syntax of PYTHONPATH is the same as that of the shell variable PATH.

Here is a typical PYTHONPATH from a Windows system −

PYTHON CODE

set PYTHONPATH = c:\python20\lib;

And here is a typical PYTHONPATH from a UNIX system −

PYTHON CODE

set PYTHONPATH = /usr/local/lib/python

Namespaces and Scoping

Variables are names (identifiers) that map to objects. Anamespaceis a dictionary of variable names (keys) and their corresponding objects (values).

A Python statement can access variables in alocal namespaceand in theglobal namespace. If a local and a global variable have the same name, the local variable shadows the global variable.
Each function has its own local namespace. Class methods follow the same scoping rule as ordinary functions.
Python makes educated guesses on whether variables are local or global. It assumes that any variable assigned a value in a function is local.
In order to assign a value to a global variable within a function, you must first use the global statement.
The statementglobal VarNametells Python that VarName is a global variable. Python stops searching the local namespace for the variable.

Example

For example, we define a variableMoneyin the global namespace. Within the functionMoney, we assignMoneya value, therefore Python assumesMoneyas a local variable. However, we accessed the value of the local variableMoneybefore setting it, so an UnboundLocalError is the result. Uncommenting the global statement fixes the problem.

PYTHON CODE

Money = 2000
def AddMoney():
   # Uncomment the following line to fix the code:
   # global Money
   Money = Money + 1
print (Money)
AddMoney()
print (Money)

Module Attributes

In Python, a module is an object of module class, and hence it is characterized by attributes.

Following are the module attributes −

file returns the physical name of the module.
package returns the package to which the module belongs.
doc returns the docstring at the top of the module if any
dict returns the entire scope of the module
name returns the name of the module

Example

Assuming that the following code is saved asmymodule.py

PYTHON CODE

"The docstring of mymodule"
def sum(x,y):
   return x+y

def average(x,y):
   return (x+y)/2
   
def power(x,y):
   return x**y

Let us check the attributes of mymodule by importing it in the following script −

PYTHON CODE

import mymodule

print ("__file__ attribute:", mymodule.__file__)
print ("__doc__ attribute:", mymodule.__doc__)
print ("__name__ attribute:", mymodule.__name__)

It will produce the followingoutput−

PYTHON CODE

__file__ attribute: C:\math\examples\mymodule.py
__doc__ attribute: The docstring of mymodule
__name__ attribute: mymodule

The nameAttribute

The name attribute of a Python module has great significance. Let us explore it in more detail.

In an interactive shell, name attribute returns ‘main’

PYTHON CODE

&gt;&gt;&gt; __name__
'__main__'

If you import any module in the interpreter session, it returns the name of the module as the name attribute of that module.

PYTHON CODE

&gt;&gt;&gt; import math
&gt;&gt;&gt; math.__name__
'math'

From inside a Python script, the name attribute returns ‘main’

PYTHON CODE

#example.py
print ("__name__ attribute within a script:", __name__)

Run this in the command terminal −

PYTHON CODE

__name__ attribute within a script: __main__

This attribute allows a Python script to be used as executable or as a module. Unlike in C++, Java, C# etc., in Python, there is no concept of the main() function. The Python program script with .py extension can contain function definitions as well as executable statements.

Savemymodule.pyand with the following code −

PYTHON CODE

"The docstring of mymodule"
def sum(x,y):
   return x+y
   
print ("sum:",sum(10,20))

You can see that sum() function is called within the same script in which it is defined.

PYTHON CODE

sum: 30

Now let us import this function in another scriptexample.py.

PYTHON CODE

import mymodule
print ("sum:",mymodule.sum(10,20))

It will produce the followingoutput−

PYTHON CODE

sum: 30
sum: 30

The output “sum:30” appears twice. Once when mymodule module is imported. The executable statements in imported module are also run. Second output is from the calling script, i.e.,example.pyprogram.

What we want to happen is that when a module is imported, only the function should be imported, its executable statements should not run. This can be done by checking the value of name. If it is main, means it is being run and not imported. Include the executable statements like function calls conditionally.

Addifstatement inmymodule.pyas shown −

PYTHON CODE

"The docstring of mymodule"
def sum(x,y):
   return x+y

if __name__ == "__main__":
   print ("sum:",sum(10,20))

Now if you runexample.pyprogram, you will find that the sum:30 output appears only once.

PYTHON CODE

sum: 30

The dir( ) Function

The dir() built-in function returns a sorted list of strings containing the names defined by a module.

The list contains the names of all the modules, variables and functions that are defined in a module. Following is a simple example −

PYTHON CODE

# Import built-in module math
import math

content = dir(math)
print (content)

When the above code is executed, it produces the following result −

PYTHON CODE

['__doc__', '__file__', '__name__', 'acos', 'asin', 'atan', 
'atan2', 'ceil', 'cos', 'cosh', 'degrees', 'e', 'exp', 
'fabs', 'floor', 'fmod', 'frexp', 'hypot', 'ldexp', 'log',
'log10', 'modf', 'pi', 'pow', 'radians', 'sin', 'sinh', 
'sqrt', 'tan', 'tanh']

The reload() Function

Sometimes you may need to reload a module, especially when working with the interactive interpreter session of Python.

Assume that we have a test module (test.py) with the following function −

PYTHON CODE

def SayHello(name):
   print ("Hi {}! How are you?".format(name))
   return

We can import the module and call its function from Python prompt as −

PYTHON CODE

&gt;&gt;&gt; import test
&gt;&gt;&gt; test.SayHello("Deepak")
Hi Deepak! How are you?

However, suppose you need to modify the SayHello() function, such as −

PYTHON CODE

def SayHello(name, course):
   print ("Hi {}! How are you?".format(name))
   print ("Welcome to {} Tutorial by CodesCompiler".format(course))
   return

Even if you edit the test.py file and save it, the function loaded in the memory won’t update. You need to reload it, using reload() function in imp module.

PYTHON CODE

&gt;&gt;&gt; import imp
&gt;&gt;&gt; imp.reload(test)
&gt;&gt;&gt; test.SayHello("Deepak", "Python")
Hi Deepak! How are you?
Welcome to Python Tutorial by CodesCompiler

Packages in Python

A package is a hierarchical file directory structure that defines a single Python application environment that consists of modules, subpackages and, sub-subpackages, and so on.

Consider a filePots.pyavailable inPhonedirectory. This file has following line of source code −

PYTHON CODE

def Pots():
   print "I'm Pots Phone"

Similar way, we have another two files having different functions with the same name as above −

Phone/Isdn.pyfile having function Isdn()
Phone/G3.pyfile having function G3()

Now, create one more file init.py inPhonedirectory −

Phone/init.py

To make all of your functions available when you’ve imported Phone, you need to put explicit import statements in init.py as follows −

PYTHON CODE

from Pots import Pots
from Isdn import Isdn
from G3 import G3

After you add these lines to init.py, you have all of these classes available when you import the Phone package.

PYTHON CODE

# Now import your Phone Package.
import Phone

Phone.Pots()
Phone.Isdn()
Phone.G3()

When the above code is executed, it produces the following result −

PYTHON CODE

I'm Pots Phone
I'm 3G Phone
I'm ISDN Phone

In the above example, we have taken example of a single functions in each file, but you can keep multiple functions in your files. You can also define different Python classes in those files and then you can create your packages out of those classes.

PYTHON - Modules

Python - Modules

Python Modules

Example of Python Module

Python Built-in Modules

Python User-defined Modules

Creating a Python Module

The import Statement

The from … import Statement

The from…import * Statement

The import … as Statement

Locating Modules

ThePYTHONPATHVariable

Namespaces and Scoping

Example

Module Attributes

Example

The __name__Attribute

The dir( ) Function

The reload() Function

Packages in Python

The nameAttribute