Introduction to Reading and Writing Files

File handling is an essential skill for any Python programmer. It allows you to store, retrieve, and manipulate data in files on your computer.

In this lesson, you’ll learn how to open, read, write, and close files using Python's built-in functions.

Opening Files

To work with a file in Python, you first need to open it using the open() function. The function takes the file name and mode as arguments:

• 'r': Read mode (default).
• 'w': Write mode.
• 'a': Append mode.
• 'b': Binary mode.

# Opening a file in read mode
file = open("example.txt", "r")
# Always remember to close the file after use
file.close()

Reading Files

You can read the contents of a file using methods like read(), readline(), and readlines():

# Reading the entire content of a file
file = open("example.txt", "r")
content = file.read()
print(content)
file.close()

Writing to Files

To write to a file, open it in write ('w') or append ('a') mode. Writing in 'w' mode overwrites the file, while 'a' mode appends to it:

# Writing to a file
file = open("example.txt", "w")
file.write("Hello, World!\n")
file.close()

Using the with Statement

The with statement simplifies file handling by automatically closing the file:

# Using with statement to open and read a file
with open("example.txt", "r") as file:
    content = file.read()
    print(content)  # File is automatically closed after this block

Appending to Files

Appending allows you to add new content to the end of an existing file without overwriting it:

# Appending to a file
with open("example.txt", "a") as file:
    file.write("This is additional content.\n")

Reading Files Line by Line

You can use a loop to read a file line by line, which is useful for large files:

# Reading a file line by line
with open("example.txt", "r") as file:
    for line in file:
        print(line.strip())  # Removes the trailing newline

Common Mistakes with File Handling

Here are some mistakes to avoid:

• Forgetting to close a file after opening it (use with statement).
• Using write mode ('w') unintentionally, which overwrites the file.
• Not handling file-related exceptions.

What Did We Learn?

In this lesson, you learned:

• How to open, read, write, and append to files in Python.
• How to use the with statement for safer file handling.
• Common mistakes to avoid when working with files.

Great job! Let’s move to the next topic.