2.3 KiB
(streams)=
Redirecting standard streams
Pyodide has three functions {js:func}pyodide.setStdin,
{js:func}pyodide.setStdout, and {js:func}pyodide.setStderr that change the
behavior of reading from {py:data}~sys.stdin and writing to {py:data}~sys.stdout and
{py:data}~sys.stderr respectively.
setStdin({stdin?, isatty?, error?}) takes a function which should take zero
arguments and return either a string or an ArrayBufferView of information read
from stdin. The isatty argument signals whether {py:func}isatty(stdin) <os.isatty> should be true
or false. If you pass error: true then reading from stdin will return an
error. If setStdin is called with no arguments, the default value is restored.
In Node the default behavior is to read from {js:data}process.stdin and in the browser
it is to throw an error.
setStdout({batched?, raw?, isattty?}) sets the standard out handler and
similarly setStderr (same arguments) sets the stdandard error handler. If a
raw handler is provided then the handler is called with a number for each
byte of the output to stdout. The handler is expected to deal with this in
whatever way it prefers. isattty again controls whether {py:func}isatty(stdout) <os.isatty>
returns true or false.
On the other hand, a batched handler is only called with complete lines of
text (or when the output is flushed). A batched handler cannot have isatty
set to true because it is impossible to use such a handler to make something
behave like a tty.
Passing neither raw nor batched sets the default behavior. In Node the
default behavior is to write directly to {js:data}process.stdout and
{js:data}process.stderr (in this case isatty depends on whether
{js:data}process.stdout and {js:data}process.stderr are ttys). In browser,
the default behavior is achieved with pyodide.setStdout({batched: console.log})
and pyodide.setStderr({batched: console.warn}).
The arguments stdin, stdout, and stderr to loadPyodide provide a
diminished amount of control compared to setStdin, setStdout, and
setStderr. They all set isatty to false and use batched processing for
setStdout and setStderr. In most cases, nothing is written or read to any of
these streams while Pyodide is starting, so if you need the added flexibility
you can wait until Pyodide is loaded and then use the pyodide.setStdxxx apis.