On 8/29/2019 10:16 AM, Eryk Sun wrote:
On 8/29/19, Rhodri James <rho...@kynesim.co.uk> wrote:
"isatty()" is a method of the io.IOBase class that checks to see
if the stream is connected to a tty, or to use less jargon, if it is
interactive. "tty" was I think originally an abbreviation for
"teletype", but nowadays it refers to any terminal, anywhere you
get a command line prompt.
In Windows, isatty() is true for any character-type file.
Does that mean one that can either send or receive data a character at a
time, as opposed to a block at a time?
This does
not necessarily mean an interactive stream. In particular, NUL is a
character device:
C:\>python -c "import sys;print(sys.stderr.isatty())" 2>NUL
True
Aha. So this is why
https://pubs.opengroup.org/onlinepubs/009695399/functions/isatty.html
follows the doc for isatty, which says 'associated with a terminal
device', with an information section that contradicts that with
"The isatty() function does not necessarily indicate that a human being
is available for interaction via fildes. It is quite possible that
non-terminal devices are connected to the communications line."
But a pipe is not:
C:\>python -c "import sys;print(sys.stderr.isatty())" 2>&1 | more
False
What makes a pipe on Windows not a character file? Is data sent between
processes a block at a time? Are posix pipes different?
https://stackoverflow.com/questions/1312922/detect-if-stdin-is-a-terminal-or-pipe
notes that 'cat | python' does not launch the REPL' and asks how to
detect if connected to a pipe (or not a terminal). I presume the system
in not Windows. The answers include both isatty and a stat call. For
CPython, the answer is in the code. On Windows, I got the following
with one 'Enter' after 'NUL'
---
C:\Users\Terry>python 0<NUL
Python 3.7.4 (tags/v3.7.4:e09359112e, Jul 8 2019, 20:34:20) [MSC v.1916
64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>>
---
It appears that Python sees NUL as a tty, as you said, and the first
read indicated EndOfFile, nearly the same as entering ^Z<enter>.
I don't understand the following.
---
C:\Users\Terry>python -c "print('hello\n') | python
hello
Traceback (most recent call last):
File "<string>", line 1, in <module>
NameError: name 'python' is not defined
---
This illustrates that pipe input is not seen as a tty as python exits
without a prompt.
---
C:\Users\Terry>py -c "print('''print('alpha')''')" | py
alpha
C:\Users\Terry>
---
--
Terry Jan Reedy
--
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