Python 🐍 Functions And File Handling 📂

Introduction

 

Python Basics cover all the Python Datatypes and Python Tokens. After that, we learned the Python Flow Controls. Let's keep moving forward with Python Functions and Python Class/Objects and Python File Handling.

 

What is a Function?

 

A function is a block of organized, reusable sets of instructions used to perform some related actions. A function is a code that might to use again and again at some point in time.

 

 

User-Defined Function

 

It is the function which is defined by the user.

 

Syntax

def function_name(arg1, arg2, arg3,…):
statements….
return
[expression]

Example

 

In this example: a and b are arguments and it is stored in sum function.

 

 

Built-In Functions

 

It is the predefined set of functions in Python.

• abs(): It returns the absolute value of a number.
• all(): It returns true if all items in an iterable object are true.
• any(): It returns true if any items in an iterable object are true.
• ascii(): It returns a readable version of an object. It replaces non-ascii characters with an escape character.
• bin(): It returns the binary versions of numbers.
• bool(): It returns the Boolean value of specified objects.

And many more built-in functions are available.

 

How to call a Function?

 

There are two ways to call a function either by PASSING A VALUE or PASSING REFERENCE.

 

PASSING BY VALUE

 

Example

 

 

 

PASSING BY REFERENCE

 

Example

 

 

Lambda Function

 

Lambda function is a small anonymous function of Python. It means it’s not having the name of the function. Lambda function can take any number of arguments but with only one expression.

 

Note

A lambda function cannot contain more than one expression.

 

Syntax

lambda arguments: expression

Example 

 

 

def Functions VS Lambda Functions

 

 

2. A normal function declared with the def keyword.

 

Anonymous functions are declared with the lambda keyword.

 

3. We can say that a+b is a normal function. On the other hand, k=a+b is the lambda function.

 

Plus Point of Lambda Function

 

An anonymous function inside a normal function,

 

Example

 

 

Python Classes/Objects

• Python is an object-oriented programming language.
• Moreover, we can say that everything in Python is an object, with properties and methods.
• A class is a “blueprint” for creating an object.

Syntax

Define Class
class class_name:
define objects/methods/functions

Example

class py_class:
a=3
Call an Object:
Object_nm=class_name()
Print statement…

Example

Obj1=py_class()
print(Obj1.a)

 

 

File Handling in Python

 

File handling is an important part of a web application.

 

There are four features of File handling in Python,

1. Open
2. Read
3. Write/Create
4. Delete

OPEN

 

Python users can take open() to open a file. It takes two parameters, filename and mode.

 

Syntax

f=open(“Path of the File”,mode)

mode

 

There are four different types of modes,

• “r” READ: READ mode has a default value. Opens a file for any errors in the file does not exists.
• "a” APPEND: APPEND mode opens a file for appending, creates the file if it does not exists.
• “w” WRITE: WRITE mode opens a file for writing, creates the file if it does not exists.
• “x” CREATE: CREATE mode creates the specified file returns an error if the file with the same name exists

Example 

 

 

Let’s check that filehandling.txt is created in D:/meta/ folder…

 

 

READ

 

It is to read the contents of the file.

 

Example

 

 

Read some parts of the file,

 

Example 

 

 

For example, if we want to read the first 3 characters of the file:

 

Reading the first line from the file we will use the readline() function,

 

Example

 

 

 

If I want to read the first two lines of my file then I have to readline() twice.

 

Example 

 

 

 

Loop through the file

 

If I want to read my file contents line by line then I have to use a FOR Loop. 

 

Example 

 

 

 

WRITE/CREATE

 

Writing and creating this mode used when we would like to add to the file or create a new file. To write to an existing file, you must add a parameter to the open() function.

• a-Append: will append to the end of the file.
• w-Write: will overwrite any existing content. 

Here, the write() function is going to be used.

 

Example

 

 

 

This is for append. Now we will check with write.

 

Example

 

 

Creating a new file

 

We can create a file using x-create, a-append or w-write modes.

• x-Create: It creates a file, returns an error if the file already exists.
• a-Append: Create a file if the specified file doesn’t exist.
• w-Write: Create a file if the specified file doesn’t exist.

Example

 

 

 

f=open(“D:/meta/filehandling.txt”, “x”) This will create a file myfile.txt, otherwise, it will return an error if it already exists.

 

 

DELETE

 

When we want to import an OS module we have to delete the file. Before deleting a file we must have to close that file. For closing a file we should use the close() function.

 

Syntax

import os
os.remove(“filename with path”)

Example

 

 

You can see in the folder filehandling.txt is removed.

 

Note

 

Find the file attached to this article: funcs_filehandling.rar.

 

Reference Links

• https://www.w3schools.com/python/ 
• https://thepythonguru.com/python-lambda-function/

Summary

 

In this article, we have seen all the major functions with syntax and example with the difference of def function with a lambda function. Moreover, we have seen in detail how file handling works in Python along with its modes.