File Handling

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Python allows us to read, write, create and delete files. This process is called file handling. This is what we will discuss in this lesson

The `open()` function

The open() function allows us to read, create and update files

It takes 2 parameters:

file - the file or file path to be opened
mode - the mode in which a file is opened for

The mode is a string that can either be any of the following:

Mode	Meaning
`'r'`	Open a file for reading
`'w'`	Open a file for writing, creates the file if it does not exist
`'a'`	Open a file for writing, appends to the end of the file
`'x'`	Open a file for creating, fails if file already exists

Python File reading

To better explain this, let us say we have a folder named my_folder.

Inside my_folder we have the following files:

demo.txt
main_code.py

The content of the demo.txt file is the following

Hello World!
I love Python

Now our goal is to read the content of the demo.txt file and then print it using the main_code.py file

To achieve this, we will use the open() function with 'r' mode.

# this is main code

file = open(
    file='demo.txt',
    mode='r'
)
content = file.read()
print(content)

Hello World!
I love Python

Reading Lines

We can also read each line using the readline() method.

# this is main_code.py

file = open(
    file='demo.txt',
    mode='r'
)

first_line = file.readline()
second_line = file.readline()

print('First line:', first_line)
print('Second line:', second_line)

First line: Hello World!

Second line: I love Python

Writing a File

In simplest terms, writing a file means modifying the content of a file or creating it if it doesnot exist yet.

In Python, there are 2 modes to write to file.

'w' - overwrites content of a file, creates file if it does not exist
'a' - appends content to the end of a file, creates the file if it does not exist

Example To better explain this, lets say we have a folder named my_folder. Inside my_folder we have the following files

demo.txt
main_code.py

The content of the demo.txt file is the following

I love Python

In this example, we will use the 'w' mode which will overwrite(replace) the content of the file

# this is main_code.py

file = open(
    file='demo.txt',
    mode='w'
)
file.write('I love JavaScript')
file.close()

When the above code is run, the content of the file demo.txt will be this:

I love JavaScript

Another example, this time we will use the a mode which will append or add content to the end of the file

# this is main_code.py

file = open(
    file='demo.txt',
    mode='a'
)
file.write(' and JavaScript')
file.close()

When the above script is run, the content of the demo.txt file will be this:

I love Python and JavaScript

Deleting a file

To delete a file, use the os module. The os modules contains the remove() method which we can use to delete files.

# this is main_code.py

# import os

# os.remove('demo.txt')

Exercise

Develop a simple telephone directory which saves your friends contact information in a file named directory.txt. The program should have a menu similar to the following:
```
----------------Menu-------------------------
1. Add new friend.
2. Display contact info.
3. Exit
------------------------------------------------
Enter menu number:
```
When you press “1” it should request you to enter following data:
```
---------New friend info--------
Name : Saman
Phone-No: 011-2123456
e-Mail : saman@cse.mrt.ac.lk
```
After adding new contact information it should again display the menu. When you press “2” it should display all the contact information stored in the directory.txt file as follows:

--------------Contact info---------------
Name            Tel-No          e-Mail
Kamala          077-7123123     kamala@yahoo.com
Kalani          033-4100101     kalani@gmail.com
Saman           011-2123456     saman@cse.mrt.ac.lk
-----------------------------------------