3. Writing to a File

Quiz: 0/5

In Python, you can write to files using two main modes: w and a.

Mode w (Write mode):

When you open a file in write mode w, Python will create a new file if it doesn’t exist or overwrite the content of the file if it already exists.

This means if the file already has some text, it will delete everything and start fresh.

Mode a (Append mode):

When you open a file in append mode a, Python will add new content to the end of the file, without touching or deleting the existing content.

This is useful when you want to add new data to an existing file without overwriting it.

Writing methods

.write()

Example:

with open("example.txt", "w") as file:
    file.write("Hello, World!\n")
    file.write("This is a new line.")

In this case, "Hello, World!" and "This is a new line." will be written to the file example.txt.

The .write() method allows you to write a single string to a file.

It doesn’t add a newline automatically after the string, so you need to manually include \n if you want to start a new line.

.writelines():

Example:

lines = ["First line\n", "Second line\n", "Third line\n"]
with open("example.txt", "w") as file:
    file.writelines(lines)

This will write the lines "First line", "Second line", and "Third line" to the file, each on a new line.

• The .writelines() method is used to write a list of strings to a file.
• Unlike .write(), it doesn’t automatically add newlines, so each string in the list should have a newline (\n) if needed.

Difference between w and a

• w (write): If you open a file in write mode w, it will overwrite any existing content in the file. This is like starting with a clean slate.

• a (append): If you open a file in append mode a, it will add new content to the end of the file without affecting the current content.

Example to illustrate:

Using w mode (overwrite):

with open("test.txt", "w") as file:
    file.write("This is the first line.")

If test.txt already had some content, it will now only contain "This is the first line."

Using a mode (append):

with open("test.txt", "a") as file:
    file.write("\nThis is an added line.")

After this, the file test.txt will contain:

This is the first line.
This is an added line.