In python 2.x I could do this:
import sys, array
a = array.array('B', range(100))
a.tofile(sys.stdout)Now however, I get a TypeError: can't write bytes to text stream. Is there some secret encoding that I should use?
4 Answers
A better way:
import sys
sys.stdout.buffer.write(b"some binary data")
8 Comments
csl
Using
sys.stdout.buffer also lets you do things like using shutil.copyfileobj even when the source file object gives bytes, and not strings. +1
Damian Yerrick
Programs using this can't be tested in IDLE 3:
AttributeError: 'PseudoOutputFile' object has no attribute 'buffer'
Artyer
@DamianYerrick in IDLE (in Windows at least)
pythonw.exe runs IDLE, which means that there is no stdout. It is emulated with tkinter. It physically can't handle bytes. In this case, .decode('UTF-8', errors='replace') your string, or run python3 -I <filename> to get a REPL instead of using IDLE.
Kotauskas
Messes up order of writes when writing to
stderr if using along with print(file=sys.stderr).
sivann
@VincentAlex
sys.stdout.flush() |
An idiomatic way of doing so, which is only available for Python 3, is:
with os.fdopen(sys.stdout.fileno(), "wb", closefd=False) as stdout:
stdout.write(b"my bytes object")
stdout.flush()
The good part is that it uses the normal file object interface, which everybody is used to in Python.
Notice that I'm setting closefd=False to avoid closing sys.stdout when exiting the with block. Otherwise, your program wouldn't be able to print to stdout anymore. However, for other kind of file descriptors, you may want to skip that part.
8 Comments
Martin
Why do you flush? Isn't it better to let Python decide when to flush stdout?
Mikhail T.
Can't the existing channel -- such as
sys.stdout -- be somehow turned into binary mode (and then back) without opening a new one on top of it?
Yajo
I don't think so. BTW I flush because otherwise the fd will be closed. Maybe python would flush anyways... you can try and report.
Marcel
sys.stdout.buffer is in binary mode
Karl Knechtel
"Notice that I'm setting closefd=False to avoid closing sys.stdout when exiting the with block. " Is it actually valid to re-open it when it's already open, though?
|
import os
os.write(1, a.tostring())
or, os.write(sys.stdout.fileno(), …) if that's more readable than 1 for you.
answered May 25, 2009 at 23:11
Alex Martelli
887k175 gold badges1.3k silver badges1.4k bronze badges
2 Comments
Ivan Baldin
Thanks, that worked. Feels a bit hack-ish but I guess it's not that common thing to do.
mic_e
The problem with
os.write is that you'll have to check the return value, as it doesn't guarantee that everything will be written.In case you would like to specify an encoding in python3 you can still use the bytes command like below:
import os
os.write(1,bytes('Your string to Stdout','UTF-8'))
where 1 is the corresponding usual number for stdout --> sys.stdout.fileno()
Otherwise if you don't care of the encoding just use:
import sys
sys.stdout.write("Your string to Stdout\n")
If you want to use the os.write without the encoding, then try to use the below:
import os
os.write(1,b"Your string to Stdout\n")
3 Comments
Damian Yerrick
Programs using
os.write(sys.stdout.fileno(), some_bytes) won't work in IDLE. io.UnsupportedOperation: fileno
Marco smdm
@DamianYerrick: You are right...the IDLE should not be used anyway to test something like that. Shortly: try to open the IDLE (I had the python3.5.1 shell) and simply import sys and sys.stdout.fileno() it will throw you io error, because in IDLE this is not supported operation :-) It is always important to remember in which environment you are working and try to get what is possible ;) Hope this clarify your query :-) Have a nice weekend.
Kotauskas
You only mention one way of writing actual binary data to
stdout, the last one.
os.writewill work on both Py2 and Py3.