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File Operations: Reading and Writing

In this tutorial, we'll delve into an important aspect of Python programming - File Operations. More specifically, we'll focus on how to read and write files in Python. This is a crucial skill because data is often stored in files, and being able to interact with these files can significantly expand the functionality of your programs.

Opening a File​

Before you can read or write a file, you first need to open it using Python's built-in open() function. This function takes two parameters: the name of the file and the mode.

file = open("test.txt", "r")

In the example above, "test.txt" is the name of the file we want to open, and "r" is the mode. The mode determines how we interact with the file. Here are some common modes:

  • "r" - Read mode. This is the default mode, which allows you to read the file but not modify it.
  • "w" - Write mode. This mode allows you to write data into the file. If the file does not exist, it creates a new one. If it exists, it will overwrite the existing file.
  • "a" - Append mode. This mode allows you to add new data to the end of the file. It does not overwrite the existing data.
  • "x" - Exclusive Creation mode. This mode creates a new file. If the file already exists, the operation fails.

Reading a File​

Once a file is opened in read mode, you can use the read() method to read its contents.

file = open("test.txt", "r")
print(file.read())

You can also read a file line by line using the readline() method.

file = open("test.txt", "r")
print(file.readline())

When you're done with a file, you should always close it using the close() method to free up resources.

file.close()

Writing to a File​

To write to a file, you open it in write or append mode and use the write() method. 

file = open("test.txt", "w")
file.write("Hello, World!")
file.close()

This code opens "test.txt", writes "Hello, World!" to it, then closes it. If "test.txt" did not exist, the open() function would create it.

Using 'with' Statement​

While opening a file using open() and closing it using close() is perfectly valid, there's a more efficient way to handle file operations in Python - by using the with statement.

The with statement automatically takes care of closing the file once it leaves the with block, even in cases of error. This makes it a good practice to open and handle files.

with open("test.txt", "r") as file:
    print(file.read())

In this code, the with statement opens "test.txt", and the read() method reads the entire file. After this, the file is automatically closed.

And that's it! You've now learned how to read from and write to files in Python. This is a fundamental skill in Python programming, so make sure to practice it. Happy coding!