09 file handling
title: Python File Handling description: Python allows us to read, write, create and delete files. keywords: [Python File Handling, creating files in python, deleting files in python, modifying files in python, reading files in python] author: Juma Shafara date: "2023-11"¶
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 openedmode- 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.txtmain_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.txtmain_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
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