REF: Remove side-effects from importing Styler

pandas/io/formats/style.py

@@ -41,9 +41,6 @@
 from pandas.core.shared_docs import _shared_docs
 
 from pandas.io.formats.format import save_to_buffer
-
-jinja2 = import_optional_dependency("jinja2", extra="DataFrame.style requires jinja2.")
-
 from pandas.io.formats.style_render import (
     CSSProperties,
     CSSStyles,
@@ -75,22 +72,18 @@
 
     from pandas import ExcelWriter
 
-try:
-    import matplotlib as mpl
-    import matplotlib.pyplot as plt
-
-    has_mpl = True
-except ImportError:
-    has_mpl = False
-
 
 @contextmanager
 def _mpl(func: Callable) -> Generator[tuple[Any, Any], None, None]:
-    if has_mpl:
-        yield plt, mpl
-    else:
+    try:
+        import matplotlib as mpl
+        import matplotlib.pyplot as plt
+
+    except ImportError:
         raise ImportError(f"{func.__name__} requires matplotlib.")
 
+    yield plt, mpl
+
 
 ####
 # Shared Doc Strings
@@ -3424,6 +3417,10 @@ def from_custom_template(
             Has the correct ``env``,``template_html``, ``template_html_table`` and
             ``template_html_style`` class attributes set.
         """
+        jinja2 = import_optional_dependency(
+            "jinja2", extra="DataFrame.style requires jinja2."
+        )
+
         loader = jinja2.ChoiceLoader([jinja2.FileSystemLoader(searchpath), cls.loader])
 
         # mypy doesn't like dynamically-defined classes

pandas/io/formats/style_render.py

@@ -48,8 +48,6 @@
         Axis,
         Level,
     )
-jinja2 = import_optional_dependency("jinja2", extra="DataFrame.style requires jinja2.")
-from markupsafe import escape as escape_html  # markupsafe is jinja2 dependency
 
 BaseFormatter = Union[str, Callable]
 ExtFormatter = Union[BaseFormatter, Dict[Any, Optional[BaseFormatter]]]
@@ -72,13 +70,14 @@ class StylerRenderer:
     Base class to process rendering a Styler with a specified jinja2 template.
     """
 
-    loader = jinja2.PackageLoader("pandas", "io/formats/templates")
-    env = jinja2.Environment(loader=loader, trim_blocks=True)
-    template_html = env.get_template("html.tpl")
-    template_html_table = env.get_template("html_table.tpl")
-    template_html_style = env.get_template("html_style.tpl")
-    template_latex = env.get_template("latex.tpl")
-    template_string = env.get_template("string.tpl")
+    # For cached class properties defined below
+    _loader = None
+    _env = None
+    _template_html = None
+    _template_html_table = None
+    _template_html_style = None
+    _template_latex = None
+    _template_string = None
 
     def __init__(
         self,
@@ -147,6 +146,61 @@ def __init__(
             tuple[int, int], Callable[[Any], str]
         ] = defaultdict(lambda: partial(_default_formatter, precision=precision))
 
+    @classmethod
+    @property
+    def loader(cls):
+        if cls._loader is None:
+            jinja2 = import_optional_dependency(
+                "jinja2", extra="DataFrame.style requires jinja2."
+            )
+            cls._loader = jinja2.PackageLoader("pandas", "io/formats/templates")
+        return cls._loader
+
+    @classmethod
+    @property
+    def env(cls):
+        if cls._env is None:
+            jinja2 = import_optional_dependency(
+                "jinja2", extra="DataFrame.style requires jinja2."
+            )
+            cls._env = jinja2.Environment(loader=cls.loader, trim_blocks=True)
+        return cls._env
+
+    @classmethod
+    @property
+    def template_html(cls):
+        if cls._template_html is None:
+            cls._template_html = cls.env.get_template("html.tpl")
+        return cls._template_html
+
+    @classmethod
+    @property
+    def template_html_table(cls):
+        if cls._template_html_table is None:
+            cls._template_html_table = cls.env.get_template("html_table.tpl")
+        return cls._template_html_table
+
+    @classmethod
+    @property
+    def template_html_style(cls):
+        if cls._template_html_style is None:
+            cls._template_html_style = cls.env.get_template("html_style.tpl")
+        return cls._template_html_style
+
+    @classmethod
+    @property
+    def template_latex(cls):
+        if cls._template_latex is None:
+            cls._template_latex = cls.env.get_template("latex.tpl")
+        return cls._template_latex
+
+    @classmethod
+    @property
+    def template_string(cls):
+        if cls._template_string is None:
+            cls._template_string = cls.env.get_template("string.tpl")
+        return cls._template_string
+
     def _render(
         self,
         sparse_index: bool,
@@ -1778,11 +1832,11 @@ def wrapper(x):
     return wrapper
 
 
-def _str_escape(x, escape):
+def _str_escape(x, escape, markupsafe):
     """if escaping: only use on str, else return input"""
     if isinstance(x, str):
         if escape == "html":
-            return escape_html(x)
+            return markupsafe.escape(x)
         elif escape == "latex":
             return _escape_latex(x)
         elif escape == "latex-math":
@@ -1840,7 +1894,10 @@ def _maybe_wrap_formatter(
 
     # Replace chars if escaping
     if escape is not None:
-        func_1 = lambda x: func_0(_str_escape(x, escape=escape))
+        markupsafe = import_optional_dependency(
+            "markupsafe", extra="DataFrame.style requires markupsafe."
+        )
+        func_1 = lambda x: func_0(_str_escape(x, escape=escape, markupsafe=markupsafe))
     else:
         func_1 = func_0
 

pandas/tests/io/formats/style/test_format.py

@@ -12,6 +12,8 @@
 )
 
 pytest.importorskip("jinja2")
+import markupsafe
+
 from pandas.io.formats.style import Styler
 from pandas.io.formats.style_render import _str_escape
 
@@ -408,12 +410,12 @@ def test_format_decimal(formatter, thousands, precision, func, col):
 def test_str_escape_error():
     msg = "`escape` only permitted in {'html', 'latex', 'latex-math'}, got "
     with pytest.raises(ValueError, match=msg):
-        _str_escape("text", "bad_escape")
+        _str_escape("text", "bad_escape", markupsafe)
 
     with pytest.raises(ValueError, match=msg):
-        _str_escape("text", [])
+        _str_escape("text", [], markupsafe)
 
-    _str_escape(2.00, "bad_escape")  # OK since dtype is float
+    _str_escape(2.00, "bad_escape", markupsafe)  # OK since dtype is float
 
 
 def test_format_options():

pandas/tests/io/formats/style/test_style.py

@@ -1,6 +1,8 @@
 import contextlib
 import copy
 import re
+import subprocess
+import sys
 from textwrap import dedent
 
 import numpy as np
@@ -99,6 +101,23 @@ def styler(df):
     return Styler(df)
 
 
+def test_import_styler_no_side_effects():
+    # GH#52995
+    code = (
+        "import matplotlib.units as units; "
+        "import matplotlib.dates as mdates; "
+        "n_conv = len(units.registry); "
+        "import pandas as pd; "
+        "from pandas.io.formats.style import Styler; "
+        "assert len(units.registry) == n_conv; "
+        # Ensure jinja2 was not imported
+        "import sys; "
+        "assert 'jinja2' not in sys.modules; "
+    )
+    call = [sys.executable, "-c", code]
+    subprocess.check_output(call)
+
+
 @pytest.mark.parametrize(
     "sparse_columns, exp_cols",
     [