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.
Python🐍 Functions And File Handling📂

User-Defined Function

It is the function which is defined by the user.
Syntax
  1. def function_name(arg1, arg2, arg3,…):
  2. statements….
  3. return
  4. [expression]
Example
In this example: a and b are arguments and it is stored in sum function.
Python🐍 Functions And File Handling📂
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
Python🐍 Functions And File Handling📂

PASSING BY REFERENCE

Example
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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
  1. lambda arguments: expression
Example
Python🐍 Functions And File Handling📂
def Functions VS Lambda Functions
Python🐍 Functions And File Handling📂
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🐍 Functions And File Handling📂

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
  1. Define Class
  2. class class_name:
  3. define objects/methods/functions
Example
  1. class py_class:
  2. a=3
  3. Call an Object:
  4. Object_nm=class_name()
  5. Print statement…
Example
  1. Obj1=py_class()
  2. print(Obj1.a)
Python🐍 Functions And File Handling📂

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
  1. 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
Python🐍 Functions And File Handling📂
Let’s check that filehandling.txt is created in D:/meta/ folder…
Python🐍 Functions And File Handling📂

READ

It is to read the contents of the file.
Example
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Read some parts of the file,
Example
Python🐍 Functions And File Handling📂
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
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If I want to read the first two lines of my file then I have to readline() twice.
Example
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Loop through the file

If I want to read my file contents line by line then I have to use a FOR Loop.
Example
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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
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This is for append. Now we will check with write.
Example
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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
Python🐍 Functions And File Handling📂
f=open(“D:/meta/filehandling.txt”, “x”) This will create a file myfile.txt, otherwise, it will return an error if it already exists.
Python🐍 Functions And File Handling📂

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
  1. import os
  2. os.remove(“filename with path”)
Example
Python🐍 Functions And File Handling📂
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.