Add theme list up function

README.md

@@ -130,7 +130,7 @@ sub-folder. Then, set the theme using the GTTK class
 ```python
 gttk = GTTK(window, theme="THEME_NAME_HERE")
 # OR
-gttk.set_theme("THEME_NAME_HERE")
+gttk.set_gtk_theme("THEME_NAME_HERE")
 ``` 
 or you can create a `~/.gtkrc` file (the specific paths of the files 
 that are parsed are found with `GTTK().get_default_files()`) and having
@@ -142,6 +142,14 @@ gtk-theme-name = "THEME_NAME_HERE"
 This will then be applied to all GTK applications that read the resource
 file.
 
+### Listing available theme
+To list up available theme, run this function:
+```python
+gttk=GTTK(window)
+gttk.get_themes_available() #this
+```
+It return tuple of theme names.
+
 ## Screenshots
 `gttk` should work with any GTK theme you can throw at it, but below
 are the themes Yaru and Adwaita as examples.

gttk/__init__.py

@@ -81,6 +81,14 @@ def __init__(self, window: tk.Tk, theme: Optional[str] = None, theme_dir_prefix:
     def get_themes_directory(self) -> str:
         """Return the directory in which GTK looks for installed themes"""
         return self.tk.call("ttk::theme::gttk::gtkDirectory", "theme")
+
+    def get_themes_available(self) -> Tuple[str]:
+        """Return installed themes"""
+        themes=self.tk.call("ttk::theme::gttk::availableStyles")
+        if themes == '':
+            return ()
+        else:
+            return themes
 
     def get_default_files(self) -> Tuple[str]:
         """Return the files that GTK parses by default at start-up"""