Opening Files

To start working with files in Python, you must first open them. The built-in open() function requires two parameters: the filename (or path) and the mode. There are several modes available, but we will focus on three primary ones:

• 'r': Opens a file in read mode, which is used when you only need to retrieve information. An error will occur if the file does not exist.

file = open('example.txt', 'r')

• 'w': Opens a file in write mode, clearing its previous content. If the file didn’t exist, it creates a new one.

file = open('new_file.txt', 'w')

• 'a': Appends to an existing file; if the file does not exist, it behaves like 'w'.

file = open('existing_file.txt', 'a')

Writing Data to Files

To write to files, you need to call the write() method followed by closing the file. Here’s how:

data_to_save = 'Hello World!nLine Two!'

file.write(data_to_save)

file.close()

A more efficient method is to use context managers with the with statement (see Section 6).

Closing Files

Always remember to close your files after you’re finished with them. This practice frees system resources and helps avoid potential issues. You can do this manually with file.close(), but context managers offer a more streamlined approach by automatically managing resources for you.

Handling Exceptions

Sometimes, opening a file might fail due to permission issues, non-existent paths, or other errors. To manage exceptions effectively, wrap your open() calls within try-except blocks:

try:

file = open('non_existent_file.txt', 'r')

except Exception as e:

print(f'Error Occurred: {e}')

Context Managers and the 'with' Statement

Context managers ensure that resources are properly cleaned up upon completion, regardless of whether an error occurred. They simplify file management significantly. Here’s how you can use the with statement:

with open('example.txt', 'r') as file:

# Perform any needed operation here

pass

# No explicit call to .close() required!

This approach guarantees that the file object is closed, releasing associated resources automatically.

Working with Text vs Binary Files

Text mode ('r', 'w', 'a') deals with strings, while binary mode ('rb', 'wb', 'ab') works with bytes. Unless specific requirements necessitate otherwise, it’s generally advisable to stick with text mode.

Absolute vs Relative Paths

An absolute path specifies the complete location starting from the root directory, while relative paths depend on the current working directory. Here’s an example of both:

abs_path = '/home/user/documents/file.txt'

rel_path = '../folder/file.txt'

Useful Functions: os.path & shutil

Python offers numerous useful functions under the os.path module for tasks such as checking existence, obtaining file size, and splitting paths. The shutil module can be utilized for high-level file operations including copying, moving, and deleting:

import os

import shutil

if os.path.exists('file.txt'):

print("File exists.")

size = os.path.getsize('large_file.zip')

print(f'Size of large_file.zip: {size} bytes')

dest_dir = './backup/'

shutil.copytree('./files', dest_dir)

Best Practices

To ensure effective file handling in Python, adhere to the following guidelines:

• Explicitly close files or use context managers.
• Prefer the with statement over manual file closures.
• Always specify the encoding format when opening files.
• Use appropriate modes based on your intended actions.
• Choose descriptive names for variables that hold file objects.