c09_file

Chapter 9: File Handling in Python

Table of Contents:

• Chapter 9: File Handling in Python
  • Introduction to File Handling
  • File Opening Modes
  • Opening and closing a file in python
  • Reading a file
    • The newer approach using with keyword
  • Writing into a file
  • Appending into a file
  • Reading a file line by line

Introduction to File Handling

• Python is capable of handling or manipulating data stored in files.
• We can open a file using inbuilt open() function.
• While opening a file, we have to pass different modes as a parameter to specify what we're trying to do with the file.

File Opening Modes

1. r: Reading mode

   • The default mode.
   • It allows you only to read the file, not to modify it.
   • When using this mode the file must exist.

2. w: Writing mode

   • It will create a new file if it does not exist, otherwise will erase the file and allow you to write to it.

3. a: Append mode

   • It will write data to the end of the file.
   • It does not erase the file, and the file must exist for this mode

4. rb: Binary Reading mode

   • same as r but reading is forced in binary mode.
   • This is also a default choice.

5. wb: Binary Writing mode

   • same as w but writing is forced in binary mode.

6. ab: Binary Apend mode

   • same as a but appending is forced in binary mode.

7. r+: Reading mode plus Writing mode at the same time

   • This allows you to read and write into files at the same time without having to use r and w.

8. w+: Writing mode plus Reading mode at the same time.

   • If the file does not exist, a new one is made. otherwise overwritten.

9. a+: Apend mode

   • similar to w+

10. rb+: Binary Reading mode

    • same as r+ mode but forced in binary mode

11. wb+: Binary Writing mode

    • same as w+ mode but forced in binary mode

12. ab+: Binary Apend mode

    • same as a+ mode but forced in binary mode

Opening and closing a file in python

• We use open() function to open the file.
• We use file.close() method to close the file.

Basic Syntax:

file_obj = open("<filename>", "<mode>")
# do our stuff over here
file_obj.close()

Reading a file

file = open("my_file.txt", "r")
file.read()
file.close()

The newer approach using with keyword

• If we open the file with with keyword, then we do not need to explicitly close the file.
• It automatically closes the file whenever it goes out of the scope.

with open('my_file.txt', 'r') as f:
    # do our stuff here
    f.read()
print("At this point, the file is closed")

Writing into a file

with open('my_file.txt', 'w') as f:
    f.write("This is the content to the file.")

Appending into a file

with open('my_file.txt', 'a') as f:
    f.write("This is the appended content to the file.")

Reading a file line by line

with open ('my_file.txt', 'r') as f:
    for line in f:
        print(line)

we can also achieve the same result using readlines() method.

with open ('my_file.txt', 'r') as f:
    for line in f.readlines():
        print(line)