14.5. File Append

Important

• Appends data at the end of file

• Creates file if not exists

• Works with both relative and absolute path

• Fails when directory with file cannot be accessed

• mode parameter to open() function is required

• .writelines() does not add a line separator!!

14.5.1. Open File for Appending

• Python will create file if it does not exist

• By default, file is opened in text mode

• Always remember to close file

✘

>>> file = open('/tmp/myfile.txt', mode='a')   # write in text mode
>>> file = open('/tmp/myfile.txt', mode='at')  # write in text mode
>>> file = open('/tmp/myfile.txt', mode='ab')  # write in binary mode

14.5.2. Append to File

• Append line at the end of a file

• Remember to add a newline character at the end of the line

• Remember to close the file

✘

>>> line = 'This is a line\n'
>>>
>>> file = open('/tmp/myfile.txt', mode='a')
>>> file.write(line)
15
>>> file.close()

14.5.3. Context Manager

• Context managers use with ... as ...: syntax

• Context manager closes the file automatically upon block exit (dedent)

• Remember to add a newline character at the end of the line

✘

>>> line = 'This is a line\n'
>>>
>>> with open('/tmp/myfile.txt', mode='a') as file:
...     file.write(line)
15