Added comment to output/vt100 regarding isatty.

jonathanslenders · jonathanslenders · commit 7d2ef1998d0e · 2019-12-07T22:35:13.000+01:00
Also changed isatty() check into a try/except in order to avoid race
conditions. (There was still a chance that another thread would turn stdout
into a non-tty device.)
diff --git a/prompt_toolkit/output/vt100.py b/prompt_toolkit/output/vt100.py
@@ -459,8 +459,14 @@ def get_size() -> Size:
             # https://github.com/ipython/ipython/issues/10071
             rows, columns = (None, None)
 
-            if stdout.isatty():
+            # It is possible that `stdout` is no longer a TTY device at this
+            # point. In that case we get an `OSError` in the ioctl call in
+            # `get_size`. See:
+            # https://github.com/prompt-toolkit/python-prompt-toolkit/pull/1021
+            try:
                 rows, columns = _get_size(stdout.fileno())
+            except OSError:
+                pass
             return Size(rows=rows or 24, columns=columns or 80)
 
         return cls(stdout, get_size, term=term)
