Using "with open() as file" method, how to write more than once?

Question

Usually to write a file, I would do the following:

the_file = open("somefile.txt","wb")
the_file.write("telperion")

but for some reason, iPython (Jupyter) is NOT writing the files. It's pretty weird, but the only way I could get it to work is if I write it this way:

with open('somefile.txt', "wb") as the_file:
    the_file.write("durin's day\n")

with open('somefile.txt', "wb") as the_file:
    the_file.write("legolas\n")

But obviously it's going to recreate the file object and rewrite it.

Why does the code in the first block not work? How could I make the second block work?

Opening a file in `"w"` mode removes all the data in the file if it exists. — Colonel Thirty Two, Mar 05 '16 at 18:37
Try: `the_file = open("somefile.txt", "wb", buffering=False)`. — Mike Müller, Mar 05 '16 at 18:57
Lets go back to your original write. Your writes are buffered until you've either written a block of data or you close the file. So you may not see the data on disk yet. — tdelaney, Mar 05 '16 at 19:03

Antti Haapala -- Слава Україні · Accepted Answer · 2016-03-05T18:48:14.170

17

The w flag means "open for writing and truncate the file"; you'd probably want to open the file with the a flag which means "open the file for appending".

Also, it seems that you're using Python 2. You shouldn't be using the b flag, except in case when you're writing binary as opposed to plain text content. In Python 3 your code would produce an error.

Thus:

with open('somefile.txt', 'a') as the_file:
    the_file.write("durin's day\n")

with open('somefile.txt', 'a') as the_file:
    the_file.write("legolas\n")

As for the input not showing in the file using the filehandle = open('file', 'w'), it is because the file output is buffered - only a bigger chunk is written at a time. To ensure that the file is flushed at the end of a cell, you can use filehandle.flush() as the last statement.

edited Mar 05 '16 at 18:48

answered Mar 05 '16 at 18:37

Antti Haapala -- Слава Україні

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I guess the part that's confusing for me is that I'm passing this file object around to different functions so I'm declaring it as a variable. If I create the file w/ `var = open("file","w")` then how can I append to that variable later? – O.rka Mar 05 '16 at 18:44
2

@O.rka: About the buffering in the file: the `with` statement creates a context manager that takes care of calling `the_file.close()` at the end and thereby flushing the file to disk. If you quit your Jupyter-process, the files should appear. – Georg Schölly Mar 05 '16 at 18:50

Using "with open() as file" method, how to write more than once?

1 Answers1