Python write to a file returns empty file

问题:

I am trying to do simple commands to write hello world to a file:

50 complexity:test% python2.7
Python 2.7.3 (default, Feb 11 2013, 12:48:32)
[GCC 4.4.6 20120305 (Red Hat 4.4.6-4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> f=open("/export/home/vignesh/resres.txt","w")
>>> f.write("hello world")
>>> f.write("\t".join(["hello","world"]))

This returns an empty file.

回答1:

Python won't flush the file after each write. You'll either need to flush it manually using flush:

>>> f.flush()

or close it yourself with close:

>>> f.close()

When using files in a real program, it is recommended to use with:

with open('some file.txt', 'w') as f:
    f.write('some text')
    # ...

This ensures that the file will be closed, even if an exception is thrown. If you want to work in the REPL, though, you might want to stick with closing it manually, as it'll try to read the entirety of the with before trying to execute it.

回答2:

You need to close the file:

>>> f.close()

Also, I would recommend using the with keyword with opening files:

with open("/export/home/vignesh/resres.txt","w") as f:
    f.write("hello world") 
    f.write("\t".join(["hello","world"]))

It will automatically close them for you.