.write not working in Python

Question

I'm fairly new to Python so hopefully I'm just missing something obvious here, but it has me stumped. Snippet of my program below:

outFile = open('P4Output.txt', 'w') outFile.write(output) print output print "Output saved to \"P4Output.txt\"\n"

output prints correctly to the console, but if I go open up the file it's blank. If I delete the file and execute my program again, the file is created but still is empty. I used this exact same block of code in another program of mine previously and it worked, and still works. However, if I open up Python and try something simple like:

f = open('test.txt', 'w') f.write("test")

Again, test.txt is created but is left blank. What gives?

hugomg · Accepted Answer · 2023-05-25 22:48:17Z

84

Did you remember to f.close() at the end of your program?

edited May 25, 2023 at 22:48

answered May 12, 2011 at 1:08

hugomg

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2 Comments

dcrosta Over a year ago

do files not .close() themselves when the interpreter exits?

poke Over a year ago

Files are closed when Python exists, but file output is usually buffered and if there is no newline, pending output will not be flushed to the file system.

hugomg · Accepted Answer · 2013-12-05 06:30:32Z

Due to buffering, the string may not actually show up in the file until you call flush() or close(). So try to call f.close() after f.write(). Also using with with file objects is recommended, it will automatically close the file for you even if you break out of the with block early due to an exception or return statement.

with open('P4Output.txt', 'w') as f: f.write(output)

tzot · Accepted Answer · 2011-05-12 10:22:06Z

You need to do a

outFile.flush()

if you want the buffered contents to be written to the disk. If you're done writing to the file, a file.close call will implicitly flush the buffered data before closing the file.

mkrieger1 · Accepted Answer · 2022-09-05 19:01:13Z

Try to enclose your statements in a try/except block to know if something happens during opening or writing to the file:

try: outFile = open('P4Output.txt', 'w') outFile.write(output) outFile.close() except IOError as (errno, strerror): print "I/O error({0}): {1}".format(errno, strerror)

And always close your file so the system can flush your data to the file before closing it.

Soltius · Accepted Answer · 2017-03-30 12:07:13Z

-9

maybe you should use absolute path instead of relative one.

edited Mar 30, 2017 at 12:07

Soltius

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answered Mar 30, 2017 at 9:41

Andy Ding

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