9.3.1 Writing to a Text File: Introducing the with Statement

  • Many applications acquire resources
    • files, network connections, database connections and more
  • Should release resources as soon as they’re no longer needed
  • Ensures that other applications can use the resources
  • with statement
    • Acquires a resource and assigns its corresponding object to a variable
    • Allows the application to use the resource via that variable
    • Calls the resource object’s close method to release the resource
In [1]:
with open('accounts.txt', mode='w') as accounts:
    accounts.write('100 Jones 24.98\n')
    accounts.write('200 Doe 345.67\n')
    accounts.write('300 White 0.00\n')
    accounts.write('400 Stone -42.16\n')
    accounts.write('500 Rich 224.62\n')
  • Can also write to a file with print, which automatically outputs a \n, as in
    print('100 Jones 24.98', file=accounts)
In [2]:
# macOS/Linux Users: View file contents
!cat accounts.txt

100 Jones 24.98
200 Doe 345.67
300 White 0.00
400 Stone -42.16
500 Rich 224.62
In [ ]:
# Windows Users: View file contents
!more accounts.txt

Built-In Function open

  • Opens the file accounts.txt and associates it with a file object
  • mode argument specifies the file-open mode
    • whether to open a file for reading from the file, for writing to the file or both.
  • Mode 'w' opens the file for writing, creating the file if it does not exist
  • If you do not specify a path to the file, Python creates it in the current folder
  • Be careful—opening a file for writing deletes all the existing data in the file
  • By convention, the .txt file extension indicates a plain text file

Writing to the File

  • with statement assigns the object returned by open to the variable accounts in the as clause
  • with statement’s suite uses accounts to interact with the file
    • file object’s write method writes one record at a time to the file
  • At the end of the with statement’s suite, the with statement implicitly calls the file object’s close method to close the file

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