Reading/Writing Files

Python provides a variety of functions and methods for working with files. In this lecture, we'll cover how to read from and write to files in Python.

Opening a File

Before you can read from or write to a file, you need to open it. To do this, you use the open() function. The open() function takes two arguments: the filename and the mode in which you want to open the file.

The mode argument is optional, and if you don't specify it, the file will be opened in read mode by default. Here are the different modes you can use:

• 'r' - read mode (default)
• 'w' - write mode
• 'a' - append mode
• 'x' - exclusive mode (creates a new file, but fails if the file already exists)
• 'b' - binary mode
• 't' - text mode (default)

Closing a File

After you're done working with a file, you should close it using the close() method. Here's an example:

            f = open('example.txt', 'r')
            content = f.read()
            f.close()
        

Reading from a file

To read data from a file, you can use the open() function with the 'r' mode. The syntax for opening a file in read mode is as follows:

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

This will open the file named example.txt in read mode and assign it to the variable f. Once you have opened a file, you can use various methods to read data from it. Here are some of the commonly used methods:

• read(size) : This method reads the specified number of characters from the file. If no size is specified, it reads the entire file.
• readline() : This method reads a single line from the file.
• readlines() : This method reads all the lines of the file and returns a list of strings.

Here's an example of how to read data from a file:

            file = open('example.txt', 'r')
            content = file.read()
            print(content)
            file.close()
        

Writing to a file

To write data to a file, you can use the open() function with the 'w' mode. The syntax for opening a file in write mode is as follows:

            file = open('filename', 'w')
        

Once you have opened a file in write mode, you can use the write() method to write data to it. This method takes a string as an argument and writes it to the file.

Here's an example of how to write data to a file:

            file = open('example.txt', 'w')
            file.write('This is an example of writing to a file.')
            file.close()
        

Appending to a file

To append data to a file, you can use the open() function with the 'a' mode. The syntax for opening a file in append mode is as follows:

            file = open('filename', 'a')
        

Once you have opened a file in append mode, you can use the write() method to write data to it. This method takes a string as an argument and appends it to the end of the file.

Here's an example of how to append data to a file:

            file = open('example.txt', 'a')
            file.write('This is an example of appending to a file.')
            file.close()
        

Using 'with' statement:

It is a good practice to use the with statement when working with files. This statement ensures that the file is closed properly after the block of code is executed. Here's an example of how to use the with statement to read data from a file:

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

Similarly, here's an example of how to use the with statement to write data to a file:

            with open('example.txt', 'w') as file:
                file.write('This is an example of writing to a file using the with statement.')
        

And here's an example of how to use the with statement to append data to a file:

            with open('example.txt', 'a') as file:
                file.write('This is an example of appending to a file using the with statement.')
        

Conclusion

Reading and writing files is an essential skill for any Python programmer. With the techniques covered in this tutorial, you should be able to read and write files of various types and sizes in Python. Remember to always close the file when you're done using it and to handle any errors that may occur while reading or writing.