Python – Write to File

Writing to a file involves opening the file in a specific mode, writing data to it, and then closing the file to ensure that all data is saved and resources are released. Python provides a built-in function open() to handle file operations and various methods for writing data.

Opening a File for Writing

Opening a file for writing is the first step in performing write operations in Python. The open() function is used to open files in different modes, each suited for specific use cases.

The open() Function

The open() function in Python is used to open a file. It requires at least one argument, the name of the file, and can take an optional second argument that specifies the mode in which the file should be opened.

File Modes for Writing

Following are the main modes you can use to open a file for writing −

Example: Opening a File in Write Mode

This mode is used when you want to write data to a file, starting from scratch each time the file is opened −

file = open("example.txt", "w")
file.write("Hello, World!")
file.close()
print("File opened successfully!!")

Example: Opening a File in Append Mode

This mode is used when you want to add data to the end of the file without altering its existing contents −

file = open("example.txt", "a")
file.write("Appending this line.\n")
file.close()
print("File opened successfully!!")

Writing to a File Using write() Method

The write() method is used to write a single string to a file. This makes it suitable for various text-based file operations.

The write() method takes a single argument: the string that you want to write to the file. It writes the exact content of the string to the file without adding any additional characters, such as newlines.

# Open a file in write mode
with open("example.txt", "w") as file:
   file.write("Hello, World!\n")
   file.write("This is a new line.\n")
print("File opened successfully!!")

Writing to a File Using writelines() Method

The writelines() method is used to write a list of strings to a file. Each string in the list is written to the file sequentially without adding any newline characters automatically.

# List of lines to write to the file
lines = ["First line\n", "Second line\n", "Third line\n"]
# Open a file in write mode
with open("example.txt", "w") as file:
    file.writelines(lines)
print("File opened successfully!!")

Writing to a New File

Writing to a new file in Python involves creating a new file (or overwriting an existing one) and writing the desired content to it. Here, we will explain the steps involved in writing to a new file −

• Open the File − Use the open() function to create or open a file in write mode (“w” or “wb” for binary files).
• Write Data − Use the write() or writelines() method to write data to the file.
• Close the File − Ensure the file is properly closed after writing, generally using the “with” statement for automatic handling.

# Open a file
fo = open("foo.txt", "w")
fo.write("Python is a great language.\nYeah its great!!\n")
# Close opened file
fo.close()

Writing to a New File in Binary Mode

By default, read/write operations on a file object are performed on text string data. If we need to handle files of different types, such as media files (mp3), executables (exe), or pictures (jpg), we must open the file in binary mode by adding the ‘b’ prefix to the read/write mode.

Writing Binary Data to a File

To write binary data to a file, open the file in binary write mode (‘wb’). The following example demonstrates this −

# Open a file in binary write mode
with open('test.bin', 'wb') as f:
   # Binary data
   data = b"Hello World"  
   f.write(data)

Converting Text Strings to Bytes

Conversion of a text string to bytes can be done using the encode() function. This is useful when you need to write text data as binary data −

# Open a file in binary write mode
with open('test.bin', 'wb') as f:
   # Convert text string to bytes
   data = "Hello World".encode('utf-8')  
   f.write(data)

Writing to an Existing File

When an existing file is opened in write mode (‘w’), its previous contents are erased. Opening a file with write permission treats it as a new file. To add data to an existing file without erasing its contents, you should open the file in append mode (‘a’).

# Open a file in append mode
fo = open("foo.txt", "a")
text = "TutorialsPoint has a fabulous Python tutorial"
fo.write(text)
# Close opened file
fo.close()

Writing to a File in Reading and Writing Modes

When a file is opened for writing using ‘w’ or ‘a’, it is not possible to perform write operations at any earlier byte position in the file. The ‘w+’ mode, however, allows both reading and writing operations without closing the file. The seek() function is used to move the read/write pointer to any desired byte position within the file.

Using the seek() Method

The seek() method is used to set the position of the read/write pointer within the file. The syntax for the seek() method is as follows −

fileObject.seek(offset[, whence])

Example

The following program demonstrates how to open a file in read-write mode (‘w+’), write some data, seek a specific position, and then overwrite part of the file’s content −

# Open a file in read-write mode
fo = open("foo.txt", "w+")
# Write initial data to the file
fo.write("This is a rat race")
# Move the read/write pointer to the 10th byte
fo.seek(10, 0)
# Read 3 bytes from the current position
data = fo.read(3)
# Move the read/write pointer back to the 10th byte
fo.seek(10, 0)
# Overwrite the existing content with new text
fo.write('cat')
# Close the file
fo.close()

Key Takeaway: Master file writing with open() modes (‘w’, ‘a’, ‘w+’), write(), writelines(), and seek()—essential tools for file manipulation!