file access - What is sys.stdin.fileno() in python -

i sorry if it's basic or asked before (i googled couldn't find simple & satisfactory explanation).

i want know sys.stdin.fileno() is?

i saw in code , didn't understand does. here's actual code block,

fileno = sys.stdin.fileno() if fileno not none:     new_stdin = os.fdopen(os.dup(fileno))

i executed print sys.stdin.fileno() in python command line , returned 0.

i searched google, , this (nullage.com) reference find, says,

fileno() -> integer "file descriptor".

this needed lower-level file interfaces, such os.read().

so, mean?

file descriptor low-level concept, it's integer represents open file. each open file given unique file descriptor.

in unix, convention, 3 file descriptors 0, 1, , 2 represent standard input, standard output, , standard error, respectively.

>>> import sys >>> sys.stdin.fileno() 0 >>> sys.stdout.fileno() 1 >>> sys.stderr.fileno() 2

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