Modifed Coding-style-guide.md

Coding-style-guide.md

@@ -18,25 +18,33 @@ If you use [Sublime Text](http://www.sublimetext.com/), consider installing the
 
 
 ## Python
+
+#### Black
+Oppia uses [Black](https://black.readthedocs.io/en/stable/) as the standard Python code formatter.  
+Black enforces a consistent, opinionated style automatically and is run as a pre-commit hook.  
+
+- **Automatic formatting:** Black runs every time you make a commit to ensure consistent code style.
+- **Manual formatting:** You can format a specific file manually using:
+  ```bash
+  black /home/dev/opensource/oppia/core/controllers/android.py
+
+
 - Consider using a frozenset or tuple to a list, if the data structure is not meant to be subsequently modified. This applies especially to constants.
 - If you need to raise an Exception, just do `raise Exception` -- no need to define custom exceptions. We tend to use exceptions fairly sparingly, though.
 - Otherwise, please follow the [Google Python style guide](https://github.com/google/styleguide/blob/gh-pages/pyguide.md). In particular:
   - There should be two empty lines before any top-level class or function definition.
   - It's OK for the initial documentation string to be more than one line long.
   - Prefer string interpolation over concatenation -- e.g. prefer: `'My string %s' % varname` to `'My string ' + varname`.
-  - When indenting from an open parenthesis ('('), prefer indenting by 4 rather than indenting from the position of the parenthesis. e.g., prefer:
-
-    ```
-      my_function_with_a_really_long_name(
-          'abc', 'def', None)
-    ```
-
-    over
-
-    ```
-      my_function_with_a_really_long_name('abc',
-                                          'def',
-                                          None)
+  - **Indentation inside parentheses:**  
+    Let [Black](https://black.readthedocs.io/en/stable/) handle indentation and line breaks automatically.  
+    Do **not** manually align to the opening parenthesis or indent by a fixed number of spaces.  
+    For example, Black will format code like this:
+    ```python
+    my_function_with_a_really_long_name(
+        "abc",
+        "def",
+        None,
+    )
     ```
   - Docstrings should start with """ and end with """. The content of each docstring should be left-aligned. For example: