fix: importing manim should not trigger pygments.styles.get_all_styles (#3797)

* fix: importing manim should not trigger pygments.styles.get_all_styles

Removed the Code.styles_list attribute.

Rewrote the documentation to say that a list of all styles can be generated by calling list(pygments.styles.get_all_styles()).

The example in the docstring of Code was rewritten to use an explicit code style name.

* fix: small change to documentation

* Added potential class method to get available code styles.

* Adding typehints to newly-added attributes.

Co-authored-by: adeshpande <110117391+JasonGrace2282@users.noreply.github.com>

* Removing unnecessary lines.

Co-authored-by: adeshpande <110117391+JasonGrace2282@users.noreply.github.com>

---------

Co-authored-by: adeshpande <110117391+JasonGrace2282@users.noreply.github.com>

Author: goldenphoenix713

manim/mobject/text/code_mobject.py

@@ -12,11 +12,11 @@
 from pathlib import Path
 
 import numpy as np
-from pygments import highlight
+from pygments import highlight, styles
 from pygments.formatters.html import HtmlFormatter
 from pygments.lexers import get_lexer_by_name, guess_lexer_for_filename
-from pygments.styles import get_all_styles
 
+# from pygments.styles import get_all_styles
 from manim.constants import *
 from manim.mobject.geometry.arc import Dot
 from manim.mobject.geometry.polygram import RoundedRectangle
@@ -25,8 +25,6 @@
 from manim.mobject.types.vectorized_mobject import VGroup
 from manim.utils.color import WHITE
 
-__all__ = ["Code"]
-
 
 class Code(VGroup):
     """A highlighted source code listing.
@@ -63,7 +61,7 @@ class Code(VGroup):
             background_stroke_width=1,
             background_stroke_color=WHITE,
             insert_line_no=True,
-            style=Code.styles_list[15],
+            style="emacs",
             background="window",
             language="cpp",
         )
@@ -127,7 +125,9 @@ def construct(self):
     line_no_buff
         Defines the spacing between line numbers and displayed code. Defaults to 0.4.
     style
-        Defines the style type of displayed code. You can see possible names of styles in with :attr:`styles_list`. Defaults to ``"vim"``.
+        Defines the style type of displayed code. To see a list possible
+        names of styles call :meth:`get_styles_list`.
+        Defaults to ``"vim"``.
     language
         Specifies the programming language the given code was written in. If ``None``
         (the default), the language will be automatically detected. For the list of
@@ -156,7 +156,7 @@ def construct(self):
     # For more information about pygments.lexers visit https://pygments.org/docs/lexers/
     # from pygments.lexers import get_all_lexers
     # all_lexers = get_all_lexers()
-    styles_list = list(get_all_styles())
+    _styles_list_cache: list[str] | None = None
     # For more information about pygments.styles visit https://pygments.org/docs/styles/
 
     def __init__(
@@ -288,6 +288,20 @@ def __init__(
             )
         self.move_to(np.array([0, 0, 0]))
 
+    @classmethod
+    def get_styles_list(cls):
+        """Get list of available code styles.
+
+        Returns
+        -------
+        list[str]
+            The list of available code styles to use for the ``styles``
+            argument.
+        """
+        if cls._styles_list_cache is None:
+            cls._styles_list_cache = list(styles.get_all_styles())
+        return cls._styles_list_cache
+
     def _ensure_valid_file(self):
         """Function to validate file."""
         if self.file_name is None: