Lazily import pygments in TerminalWriter

changelog/14948.improvement.rst

@@ -0,0 +1,6 @@
+``pygments`` is no longer imported when the ``_pytest._io.TerminalWriter``
+module is loaded. It is now imported lazily, only when source code is actually
+syntax-highlighted (e.g. when rendering a traceback with color output enabled).
+This avoids importing the relatively heavy ``pygments`` package on runs that
+don't need it (notably runs without markup, such as most CI executions),
+slightly reducing pytest's startup time.

src/_pytest/_io/terminalwriter.py

@@ -9,17 +9,17 @@
 from typing import final
 from typing import Literal
 from typing import TextIO
-
-import pygments
-from pygments.formatters.terminal import TerminalFormatter
-from pygments.lexer import Lexer
-from pygments.lexers.diff import DiffLexer
-from pygments.lexers.python import PythonLexer
+from typing import TYPE_CHECKING
 
 from ..compat import assert_never
 from .wcwidth import wcswidth
 
 
+if TYPE_CHECKING:
+    from pygments.formatters.terminal import TerminalFormatter
+    from pygments.lexer import Lexer
+
+
 # This code was initially copied from py 1.8.1, file _io/terminalwriter.py.
 
 
@@ -206,6 +206,9 @@ def _write_source(self, lines: Sequence[str], indents: Sequence[str] = ()) -> No
             self.line(indent + new_line)
 
     def _get_pygments_lexer(self, lexer: Literal["python", "diff"]) -> Lexer:
+        from pygments.lexers.diff import DiffLexer
+        from pygments.lexers.python import PythonLexer
+
         if lexer == "python":
             return PythonLexer()
         elif lexer == "diff":
@@ -214,6 +217,9 @@ def _get_pygments_lexer(self, lexer: Literal["python", "diff"]) -> Lexer:
             assert_never(lexer)
 
     def _get_pygments_formatter(self) -> TerminalFormatter:
+        import pygments
+        from pygments.formatters.terminal import TerminalFormatter
+
         from _pytest.config.exceptions import UsageError
 
         theme = os.getenv("PYTEST_THEME")
@@ -239,6 +245,8 @@ def _highlight(
         if not source or not self.hasmarkup or not self.code_highlight:
             return source
 
+        import pygments
+
         pygments_lexer = self._get_pygments_lexer(lexer)
         pygments_formatter = self._get_pygments_formatter()
 

testing/test_terminal.py

@@ -2909,6 +2909,29 @@ def test_foo():
         )
 
 
+def test_terminalwriter_import_does_not_import_pygments() -> None:
+    """Importing the module must not eagerly import pygments.
+
+    pygments is imported lazily only when source is actually highlighted,
+    so pytest startup (including runs without markup) should not pay the
+    cost of importing it.
+    """
+    import subprocess
+
+    code = (
+        "import sys; "
+        "import _pytest._io.terminalwriter; "
+        "print('pygments' in sys.modules)"
+    )
+    result = subprocess.run(
+        [sys.executable, "-c", code],
+        capture_output=True,
+        text=True,
+    )
+    assert result.returncode == 0
+    assert result.stdout.strip() == "False"
+
+
 def test_raw_skip_reason_skipped() -> None:
     report = SimpleNamespace()
     report.skipped = True