8.8. Writing files

To write a file, you have to open it with mode “w” as a second parameter:

>>> fout = open('output.txt', 'w')
>>> print(fout)
<_io.TextIOWrapper name='output.txt' mode='w' encoding='cp1252'>

If the file already exists, opening it in write mode clears out the old data and starts fresh, so be careful! If the file doesn’t exist, a new one is created.

The write method of the file handle object puts data into the file, returning the number of characters written. The default write mode is text for writing (and reading) strings.

>>> line1 = "This here's the wattle,\n"
>>> fout.write(line1)

Again, the file object keeps track of where it is, so if you call write again, it adds the new data to the end.

We must make sure to manage the ends of lines as we write to the file by explicitly inserting the newline character when we want to end a line. The print statement automatically appends a newline, but the write method does not add the newline automatically.

>>> line2 = 'the emblem of our land.\n'
>>> fout.write(line2)

When you are done writing, you have to close the file to make sure that the last bit of data is physically written to the disk so it will not be lost if the power goes off.

>>> fout.close()

We should close the files which we open for read as well, but we can be a little sloppy if we are only opening a few files since Python makes sure that all open files are closed when the program ends. When we are writing files, we want to explicitly close the files so as to leave nothing to chance.

Put the following pieces of code in order so a file is opened for writing, two lines are defined, two lines are written to the file, and the file is closed. Watch out for extra code blocks.

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