From f8c0850aa18f5c3f29d3301f95e3573c544118f6 Mon Sep 17 00:00:00 2001
From: Rens <rd@answer.ai>
Date: Wed, 29 Jul 2026 15:22:44 +0200
Subject: [PATCH] Add ansi= mode to render_md: 'html' renders ANSI colors in
 pooled text as an {=html} block

---
 fastcore/nbio.py  | 10 ++++++----
 nbs/13_nbio.ipynb | 16 +++++++++++-----
 2 files changed, 17 insertions(+), 9 deletions(-)

diff --git a/fastcore/nbio.py b/fastcore/nbio.py
index 8bb7a393..440b7ded 100644
--- a/fastcore/nbio.py
+++ b/fastcore/nbio.py
@@ -542,7 +542,7 @@ def _render_md(out, html1st=True):
     mime,d = preferred_msg_out(out, html1st=html1st, include_imgs=True)
     d = _join(d)
     if not d: return None
-    if   mime=='text/plain': return 'txt', strip_ansi(d)
+    if   mime=='text/plain': return 'txt', d
     elif mime=='text/html': return 'md', fenced(d.strip(), '{=html}')
     elif mime=='application/javascript': return 'md', fenced(f'<script>{d}</script>', '{=html}')
     elif mime=='image/svg+xml': return 'md', fenced(d.strip(), '{=html}')
@@ -550,12 +550,14 @@ def _render_md(out, html1st=True):
     elif mime in ('image/jpeg','image/png'): return 'md', f'![](data:{mime};base64,{"".join(d.split())})'
     return None
 
-def render_md(outputs, html1st=True):
-    "Render notebook outputs as Markdown: text pooled into ```output fences, HTML in `{=html}` fences, markdown inlined, images as data URIs"
+def render_md(outputs, html1st=True, ansi='strip'):
+    "Render notebook outputs as Markdown: text pooled into ```output fences, HTML in `{=html}` fences, markdown inlined, images as data URIs; `ansi='html'` renders ANSI colors in pooled text as an `{=html}` block instead of stripping them"
     if (not isinstance(outputs, (list,tuple))) or (outputs and not isinstance(outputs[0],dict)): return ''
     parts,buf = [],[]
     def _flush():
-        if (txt := ''.join(buf).rstrip()): parts.append(fenced(txt, 'output'))
+        if (txt := ''.join(buf).rstrip()):
+            if ansi=='html' and '\x1b' in txt: parts.append(fenced(f'<pre><code class="ansi">{ansi2html(txt)}</code></pre>', '{=html}'))
+            else: parts.append(fenced(strip_ansi(txt), 'output'))
         buf.clear()
     for out in concat_streams(outputs):
         if not (r := _render_md(out, html1st=html1st)): continue
diff --git a/nbs/13_nbio.ipynb b/nbs/13_nbio.ipynb
index c3a0c409..fd1b906e 100644
--- a/nbs/13_nbio.ipynb
+++ b/nbs/13_nbio.ipynb
@@ -2028,7 +2028,7 @@
     "    mime,d = preferred_msg_out(out, html1st=html1st, include_imgs=True)\n",
     "    d = _join(d)\n",
     "    if not d: return None\n",
-    "    if   mime=='text/plain': return 'txt', strip_ansi(d)\n",
+    "    if   mime=='text/plain': return 'txt', d\n",
     "    elif mime=='text/html': return 'md', fenced(d.strip(), '{=html}')\n",
     "    elif mime=='application/javascript': return 'md', fenced(f'<script>{d}</script>', '{=html}')\n",
     "    elif mime=='image/svg+xml': return 'md', fenced(d.strip(), '{=html}')\n",
@@ -2036,12 +2036,14 @@
     "    elif mime in ('image/jpeg','image/png'): return 'md', f'![](data:{mime};base64,{\"\".join(d.split())})'\n",
     "    return None\n",
     "\n",
-    "def render_md(outputs, html1st=True):\n",
-    "    \"Render notebook outputs as Markdown: text pooled into ```output fences, HTML in `{=html}` fences, markdown inlined, images as data URIs\"\n",
+    "def render_md(outputs, html1st=True, ansi='strip'):\n",
+    "    \"Render notebook outputs as Markdown: text pooled into ```output fences, HTML in `{=html}` fences, markdown inlined, images as data URIs; `ansi='html'` renders ANSI colors in pooled text as an `{=html}` block instead of stripping them\"\n",
     "    if (not isinstance(outputs, (list,tuple))) or (outputs and not isinstance(outputs[0],dict)): return ''\n",
     "    parts,buf = [],[]\n",
     "    def _flush():\n",
-    "        if (txt := ''.join(buf).rstrip()): parts.append(fenced(txt, 'output'))\n",
+    "        if (txt := ''.join(buf).rstrip()):\n",
+    "            if ansi=='html' and '\\x1b' in txt: parts.append(fenced(f'<pre><code class=\"ansi\">{ansi2html(txt)}</code></pre>', '{=html}'))\n",
+    "            else: parts.append(fenced(strip_ansi(txt), 'output'))\n",
     "        buf.clear()\n",
     "    for out in concat_streams(outputs):\n",
     "        if not (r := _render_md(out, html1st=html1st)): continue\n",
@@ -2088,7 +2090,11 @@
     "\n",
     "test_eq(render_md([mk_display(image_png='abc')]), '![](data:image/png;base64,abc)')\n",
     "test_eq(render_md([mk_error('oops')]), fenced('oops', 'output'))\n",
-    "test_eq(render_md([mk_stream('stdout', 'a `` b\\n')]), '```output\\na `` b\\n```')"
+    "test_eq(render_md([mk_stream('stdout', 'a `` b\\n')]), '```output\\na `` b\\n```')\n",
+    "s = '\\x1b[1;31mred\\x1b[0m <b>\\n'\n",
+    "test_eq(render_md([mk_stream('stdout', s)]), fenced('red <b>', 'output'))\n",
+    "h = render_md([mk_stream('stdout', s)], ansi='html')\n",
+    "assert h.startswith('```{=html}') and 'ansi-red-intense-fg' in h and '&lt;b&gt;' in h"
    ]
   },
   {