< Scope
Mutability >

A file is where data is stored. Python allows you to:

  • Read data from files.
  • Write data to files.
  • Manage files (e.g., delete or rename them).

Files can store text (.txt) or binary data (images, videos, etc.).

2. Opening a File

To work with files, you need to open them first using the open() function.

file = open("example.txt", "r")  # Opens the file 'example.txt' in read mode

Common Modes:

  • "r": Read (default mode).
  • "w": Write (creates a new file or overwrites an existing one).
  • "a": Append (adds data to an existing file).
  • "rb"/"wb": Read/Write binary files.

3. Reading Files

Example 1: Read the Entire File

with open("example.txt", "r") as file:
    content = file.read()
    print(content)

Explanation:

  • with open(...) as file: Automatically closes the file after the block is done.
  • file.read(): Reads the whole file content.

Sample Output:

Hello, this is an example text file.
It has multiple lines of text.

Example 2: Read Line by Line

with open("example.txt", "r") as file:
    for line in file:
        print(line.strip())  # `.strip()` removes extra spaces or newline characters

Sample Output:

Hello, this is an example text file.
It has multiple lines of text.

4. Writing to Files

Use "w" mode to write new data. Be careful—it will overwrite the file!

with open("output.txt", "w") as file:
    file.write("Python makes file handling easy!\n")
    file.write("This is another line.\n")

Sample Output in output.txt:

Python makes file handling easy!
This is another line.

5. Appending to Files

Use "a" mode to add content without overwriting.

with open("output.txt", "a") as file:
    file.write("This is an appended line.\n")

Updated output.txt:

Python makes file handling easy!
This is another line.
This is an appended line.

6. Checking if a File Exists

Sometimes, you want to avoid errors if a file doesn’t exist. Use the os module.

import os

if os.path.exists("example.txt"):
    print("The file exists!")
else:
    print("The file does not exist.")

Sample Output:

The file exists!

7. Deleting a File

Use os.remove() to delete files.

import os

if os.path.exists("output.txt"):
    os.remove("output.txt")
    print("File deleted!")
else:
    print("File not found.")

Sample Output:

File deleted!

8. Writing a List of Data to a File

You can write multiple lines using a list.

lines = ["First line\n", "Second line\n", "Third line\n"]

with open("list_output.txt", "w") as file:
    file.writelines(lines)

Output in list_output.txt:

First line
Second line
Third line

9. Reading Files into a List

You can read all lines into a list for easy processing.

with open("list_output.txt", "r") as file:
    lines = file.readlines()
    print(lines)

Sample Output:

['First line\n', 'Second line\n', 'Third line\n']

10. Working with CSV Files

Python has a built-in csv module to handle comma-separated values.

Writing a CSV File:

import csv

data = [["Name", "Age"], ["Alice", 25], ["Bob", 30]]

with open("data.csv", "w", newline="") as file:
    writer = csv.writer(file)
    writer.writerows(data)

Sample data.csv:

Name,Age
Alice,25
Bob,30

Reading a CSV File:

import csv

with open("data.csv", "r") as file:
    reader = csv.reader(file)
    for row in reader:
        print(row)

Sample Output:

['Name', 'Age']
['Alice', '25']
['Bob', '30']

11. File Paths

You can work with files in different folders using full paths.

Example:

with open("C:/Users/YourName/Documents/example.txt", "r") as file:
    print(file.read())

12. Error Handling with Files

Avoid crashes using try-except blocks.

try:
    with open("nonexistent.txt", "r") as file:
        print(file.read())
except FileNotFoundError:
    print("The file does not exist.")

Sample Output:

The file does not exist.

13. File Management Utilities

  • Rename a File: import os os.rename("oldname.txt", "newname.txt")
  • Create a File: with open("newfile.txt", "w") as file: pass # Creates an empty file

14. Binary Files

Binary files store data like images or videos. Use "rb" and "wb" modes.

Reading Binary Files:

with open("image.jpg", "rb") as file:
    data = file.read()
    print(f"File size: {len(data)} bytes")

Writing Binary Files:

with open("copy.jpg", "wb") as file:
    file.write(data)
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Mutability >