Add support for NO_COLOR

CHANGELOG.md

@@ -20,9 +20,13 @@ You can find out backwards-compatibility policy [here](https://github.com/hynek/
 - `structlog.stdlib.BoundLogger` now has, analogously to our native logger, a full set of async log methods prefixed with an `a`: `await log.ainfo("event!")`
   [#502](https://github.com/hynek/structlog/issues/502)
 
-- The default configuration now respects the presence of `FORCE_COLOR` (regardless of its value except empty string).
+- The default configuration now respects the presence of `FORCE_COLOR` (regardless of its value, unless an empty string).
   This disables all heuristics whether it makes sense to use colors.
-  [#338](https://github.com/hynek/structlog/issues/338)
+  [#503](https://github.com/hynek/structlog/issues/503)
+
+- The default configuration now respects the presence of [`NO_COLOR`](https://no-color.org) (regardless of its value, unless an empty string).
+  This disables all heuristics whether it makes sense to use colors and overrides `FORCE_COLOR`.
+  [#504](https://github.com/hynek/structlog/issues/504)
 
 
 ### Fixed

docs/console-output.md

@@ -47,6 +47,17 @@ structlog.configure(
 ```
 
 
+## Standard Environment Variables
+
+*structlog*'s default configuration uses colors if standard out is a TTY (i.e. an interactive session).
+
+It's possible to override this behavior by setting two standard environment variables to any value except an empty string:
+
+- `FORCE_COLOR` *activates* colors, regardless of where output is going.
+- [`NO_COLOR`](https://no-color.org) *disables* colors, regardless of where the output is going and regardless the value of `FORCE_COLOR`.
+  Please note that `NO_COLOR` disables _all_ styling, including bold and italics.
+
+
 ## Disabling Exception Pretty-Printing
 
 If you prefer the default terse Exception rendering, but still want *Rich* installed, you can disable the pretty-printing by instantiating {class}`structlog.dev.ConsoleRenderer()` yourself and passing `exception_formatter=structlog.dev.plain_traceback`.

src/structlog/_config.py

@@ -36,12 +36,15 @@
     set_exc_info,
     TimeStamper(fmt="%Y-%m-%d %H:%M:%S", utc=False),
     ConsoleRenderer(
-        colors=os.environ.get("FORCE_COLOR") is not None
-        or (
-            _has_colors
-            and sys.stdout is not None
-            and hasattr(sys.stdout, "isatty")
-            and sys.stdout.isatty()
+        colors=os.environ.get("NO_COLOR", "") == ""
+        and (
+            os.environ.get("FORCE_COLOR", "") != ""
+            or (
+                _has_colors
+                and sys.stdout is not None
+                and hasattr(sys.stdout, "isatty")
+                and sys.stdout.isatty()
+            )
         )
     ),
 ]

tox.ini

@@ -79,6 +79,12 @@ set_env = FORCE_COLOR=1
 commands = python -c "import structlog; structlog.get_logger().warning('should be colorful')"
 
 
+[testenv:color-no]
+help = A visual check that NO_COLOR is working.
+set_env = NO_COLOR=1
+commands = python -c "import structlog; structlog.get_logger().warning('should be plain')"
+
+
 [testenv:docset]
 deps = doc2dash
 extras = docs