fix: prevent UnicodeEncodeError on Windows CP1252 consoles in studio setup (#4563)

* fix: prevent UnicodeEncodeError on Windows CP1252 consoles in studio setup

On Windows, `unsloth studio setup` crashes with a UnicodeEncodeError
when install_python_stack.py tries to print Unicode status glyphs
(✅, ❌, ⚠️) to a console that uses a legacy code page like CP1252.

Add a _safe_print() helper that catches UnicodeEncodeError and
gracefully degrades emoji to ASCII equivalents ([OK], [FAIL], [!]).
Replace all print() calls that emit Unicode glyphs with _safe_print().

Fixes #4509

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Replace Unicode dashes with ASCII in install_python_stack.py

Box-drawing (U+2500) and em dash (U+2014) chars in section dividers
and comments are themselves not representable on CP1252 -- replace
with plain ASCII dashes for consistency with the fix.

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Daniel Han <danielhanchen@gmail.com>

studio/install_python_stack.py

@@ -22,20 +22,20 @@ from pathlib import Path
 
 IS_WINDOWS = sys.platform == "win32"
 
-# ── Verbosity control ──────────────────────────────────────────────────────────
+# -- Verbosity control ----------------------------------------------------------
 # By default the installer shows a minimal progress bar (one line, in-place).
 # Set UNSLOTH_VERBOSE=1 in the environment to restore full per-step output:
 #   Linux/Mac:  UNSLOTH_VERBOSE=1 ./studio/setup.sh
 #   Windows:    $env:UNSLOTH_VERBOSE="1" ; .\studio\setup.ps1
 VERBOSE: bool = os.environ.get("UNSLOTH_VERBOSE", "0") == "1"
 
-# Progress bar state — updated by _progress() as each install step runs.
+# Progress bar state -- updated by _progress() as each install step runs.
 # _TOTAL counts: pip-upgrade + 7 shared steps + triton (non-Windows) + local-plugin + finalize
 # Update _TOTAL here if you add or remove install steps in install_python_stack().
 _STEP: int = 0
 _TOTAL: int = 0  # set at runtime in install_python_stack() based on platform
 
-# ── Paths ──────────────────────────────────────────────────────────────
+# -- Paths --------------------------------------------------------------
 SCRIPT_DIR = Path(__file__).resolve().parent
 REQ_ROOT = SCRIPT_DIR / "backend" / "requirements"
 SINGLE_ENV = REQ_ROOT / "single-env"
@@ -44,7 +44,39 @@ LOCAL_DD_UNSTRUCTURED_PLUGIN = (
     SCRIPT_DIR / "backend" / "plugins" / "data-designer-unstructured-seed"
 )
 
-# ── Color support ──────────────────────────────────────────────────────
+# -- Unicode-safe printing ---------------------------------------------
+# On Windows the default console encoding can be a legacy code page
+# (e.g. CP1252) that cannot represent Unicode glyphs such as ✅ or ❌.
+# _safe_print() gracefully degrades to ASCII equivalents so the
+# installer never crashes just because of a status glyph.
+
+_UNICODE_TO_ASCII: dict[str, str] = {
+    "\u2705": "[OK]",  # ✅
+    "\u274c": "[FAIL]",  # ❌
+    "\u26a0\ufe0f": "[!]",  # ⚠️  (warning + variation selector)
+    "\u26a0": "[!]",  # ⚠  (warning without variation selector)
+}
+
+
+def _safe_print(*args: object, **kwargs: object) -> None:
+    """Drop-in print() replacement that survives non-UTF-8 consoles."""
+    try:
+        print(*args, **kwargs)
+    except UnicodeEncodeError:
+        # Stringify, then swap emoji for ASCII equivalents
+        text = " ".join(str(a) for a in args)
+        for uni, ascii_alt in _UNICODE_TO_ASCII.items():
+            text = text.replace(uni, ascii_alt)
+        # Final fallback: replace any remaining unencodable chars
+        print(
+            text.encode(sys.stdout.encoding or "ascii", errors = "replace").decode(
+                sys.stdout.encoding or "ascii", errors = "replace"
+            ),
+            **kwargs,
+        )
+
+
+# -- Color support ------------------------------------------------------
 
 
 def _enable_colors() -> bool:
@@ -72,7 +104,7 @@ def _enable_colors() -> bool:
     return True  # Unix terminals support ANSI by default
 
 
-# Colors disabled — Colab and most CI runners render ANSI fine, but plain output
+# Colors disabled -- Colab and most CI runners render ANSI fine, but plain output
 # is cleaner in the notebook cell. Re-enable by setting _HAS_COLOR = _enable_colors()
 _HAS_COLOR = False
 
@@ -92,7 +124,7 @@ def _red(msg: str) -> str:
 def _progress(label: str) -> None:
     """Print an in-place progress bar for the current install step.
 
-    Uses only stdlib (sys.stdout) — no extra packages required.
+    Uses only stdlib (sys.stdout) -- no extra packages required.
     In VERBOSE mode this is a no-op; per-step labels are printed by run() instead.
     """
     global _STEP
@@ -119,7 +151,7 @@ def run(
         stderr = subprocess.STDOUT if quiet else None,
     )
     if result.returncode != 0:
-        print(_red(f"❌ {label} failed (exit code {result.returncode}):"))
+        _safe_print(_red(f"❌ {label} failed (exit code {result.returncode}):"))
         if result.stdout:
             print(result.stdout.decode(errors = "replace"))
         sys.exit(result.returncode)
@@ -129,7 +161,7 @@ def run(
 # Packages to skip on Windows (require special build steps)
 WINDOWS_SKIP_PACKAGES = {"open_spiel", "triton_kernels"}
 
-# ── uv bootstrap ──────────────────────────────────────────────────────
+# -- uv bootstrap ------------------------------------------------------
 
 USE_UV = False  # Set by _bootstrap_uv() at the start of install_python_stack()
 UV_NEEDS_SYSTEM = False  # Set by _bootstrap_uv() via probe
@@ -267,7 +299,9 @@ def patch_package_file(package_name: str, relative_path: str, url: str) -> None:
         text = True,
     )
     if result.returncode != 0:
-        print(_red(f"   ⚠️  Could not find package {package_name}, skipping patch"))
+        _safe_print(
+            _red(f"   ⚠️  Could not find package {package_name}, skipping patch")
+        )
         return
 
     location = None
@@ -277,7 +311,7 @@ def patch_package_file(package_name: str, relative_path: str, url: str) -> None:
             break
 
     if not location:
-        print(_red(f"   ⚠️  Could not determine location of {package_name}"))
+        _safe_print(_red(f"   ⚠️  Could not determine location of {package_name}"))
         return
 
     dest = Path(location) / relative_path
@@ -285,7 +319,7 @@ def patch_package_file(package_name: str, relative_path: str, url: str) -> None:
     download_file(url, dest)
 
 
-# ── Main install sequence ─────────────────────────────────────────────
+# -- Main install sequence ---------------------------------------------
 
 
 def install_python_stack() -> int:
@@ -316,7 +350,7 @@ def install_python_stack() -> int:
         req = REQ_ROOT / "extras.txt",
     )
 
-    # 3b. Extra dependencies (no-deps) — audio model support etc.
+    # 3b. Extra dependencies (no-deps) -- audio model support etc.
     _progress("extra codecs")
     pip_install(
         "Installing extras (no-deps)",
@@ -325,7 +359,7 @@ def install_python_stack() -> int:
         req = REQ_ROOT / "extras-no-deps.txt",
     )
 
-    # 4. Overrides (torchao, transformers) — force-reinstall
+    # 4. Overrides (torchao, transformers) -- force-reinstall
     _progress("dependency overrides")
     pip_install(
         "Installing dependency overrides",
@@ -393,7 +427,7 @@ def install_python_stack() -> int:
 
     # 11. Local Data Designer seed plugin
     if not LOCAL_DD_UNSTRUCTURED_PLUGIN.is_dir():
-        print(
+        _safe_print(
             _red(
                 f"❌ Missing local plugin directory: {LOCAL_DD_UNSTRUCTURED_PLUGIN}",
             ),
@@ -422,7 +456,7 @@ def install_python_stack() -> int:
         stderr = subprocess.DEVNULL,
     )
 
-    print(_green("✅ Python dependencies installed"))
+    _safe_print(_green("✅ Python dependencies installed"))
     return 0