Writing to a file

Writing to a file in Python is a fundamental operation that allows you to store data persistently. This can be done in several ways, depending on the mode in which you open the file and the type of data you’re writing. Here’s a detailed overview of writing to a file, including different methods, modes, and error handling.

Opening a File for Writing

You can open a file for writing using the open() function. There are several modes you can use:

• 'w': Write mode. Opens the file for writing and truncates the file to zero length (i.e., it deletes the content of the file if it already exists).
• 'a': Append mode. Opens the file for writing, appending to the end of the file if it exists.
• 'x': Exclusive creation. Opens the file for writing only if it does not exist. Raises a FileExistsError if the file exists.
• 'b': Binary mode. Used with other modes (e.g., 'wb', 'ab') to write binary data.
• '+': Update mode. Used with other modes (e.g., 'w+', 'a+') to open a file for updating (reading and writing).

Writing Text to a File

Using write()

The write() method writes a string to the file.

# Write mode
with open('example.txt', 'w') as file:
    file.write('Hello, world!\n')
    file.write('This is a new line.\n')

# Append mode
with open('example.txt', 'a') as file:
    file.write('Appending a new line.\n')

Using writelines()

The writelines() method writes a list of strings to the file. Each string in the list will be written exactly as it is.

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

Writing Binary Data to a File

To write binary data, open the file in binary mode ('wb', 'ab').

# Writing binary data
data = b'\x00\x01\x02\x03\x04'
with open('binary_file.bin', 'wb') as file:
    file.write(data)

Using the with Statement

Using the with statement is recommended because it ensures that the file is properly closed after its suite finishes, even if an exception is raised.

with open('example.txt', 'w') as file:
    file.write('Hello, world!')

Example: Comprehensive Writing to a File

Combining all these aspects into a comprehensive example:

def write_text_file(file_name, lines, mode='w'):
    try:
        with open(file_name, mode) as file:
            file.writelines(lines)
        print(f"Data written to {file_name} successfully.")
    except FileNotFoundError:
        print(f"The file {file_name} was not found.")
    except PermissionError:
        print(f"You do not have permission to write to the file {file_name}.")
    except Exception as e:
        print(f"An unexpected error occurred: {e}")

# Example usage
lines_to_write = ['Hello, world!\n', 'This is a new line.\n']
write_text_file('example.txt', lines_to_write, 'w')

# Appending to the same file
append_lines = ['Appending this line.\n']
write_text_file('example.txt', append_lines, 'a')