Repository: oppia/oppia

Issue:
Update docstrings in the Python backend code to follow the style guide.
We've been a bit lax about adding docstrings to code in the backend. Instead, we should be following the style guide: https://google.github.io/styleguide/pyguide.html?showone=Comments#Comments -- docstrings should define args, return values, exceptions, etc. The aim of this issue is to ensure that the backend code is properly documented; we will tackle this on a file-by-file basis.

Note: if you're a new contributor, this issue is a particularly good introductory one to tackle, since it will require reading, understanding and documenting the purpose of a file in the codebase, and help you get acquainted with how the Oppia backend is structured. It's important that you're able to communicate and write clearly, though!

Some useful tips:
-  Please follow our [style guide](https://github.com/oppia/oppia/wiki/Coding-style-guide#general) (and also the [Google Python style guide](https://google.github.io/styleguide/pyguide.html?showone=Comments#Comments)) when writing docstrings. Make sure to follow the patterns established there as closely as possible, including spacing, capitalization and punctuation. Also, it's a good idea to look at some of the existing files (see below) to get a sense of the correct format -- we recommend following this closely in order to maintain uniformity across the codebase.
- If applicable, make sure that the docstrings for all functions correctly specify the args, return values, etc. If a function has no args, you can omit the Args section; if it has no return value, you can omit the Returns section.
- If a docstring is not present in the code, or the existing one is too vague for you to understand what's going on just by looking at it, then it should be rewritten to be more clear. You'll often need to read the code as well, and do a grep on the callsites to see how it's being used, in order to get a clear understanding of what it's doing. This is good practice for learning how to navigate the codebase, and is an intended part of this project.
- If you feel that parts of the codebase are unclear or incorrectly factored, please feel free to bring this up! The whole point of docstrings is to improve code health and accessibility for new developers, so if you spot other things that can be done in service of that aim, we should also look into doing that.

**Completed:**
- [x] core.controllers.base @shaz13 
- [x] core.controllers.cron @saeedjassani
- [x] core.controllers.reader @96mohitm
- [x] core.domain.activity_domain @andromfins
- [x] core.domain.activity_services @souravsingh
- [x] core.domain.classifier_services @andromfins 
- [x] core.domain.collection_domain @domevit
- [x] core.domain.collection_services @kahkhang 
- [x] core.domain.config_services @vibhor98 
- [x] core.domain.email_manager @Oishikatta 
- [x] core.domain.exp_domain @domevit
- [x] core.domain.exp_services @DubeySandeep
- [x] core.domain.feedback_domain @terrameijar 
- [x] core.domain.feedback_jobs_continuous
- [x] core.domain.feedback_services @andimeo
- [x] core.domain.fs_domain @kartik-25 
- [x] core.domain.html_cleaner @seanlip
- [x] core.domain.param_domain @rohan-gulati
- [x] core.domain.rating_services @BojOnTheBeat 
- [x] core.domain.rights_manager @ayejay
- [x] core.domain.stats_domain @Arunabh98
- [x] core.domain.stats_jobs_continuous @Arunabh98 
- [x] core.domain.stats_jobs_one_off @zpuller
- [x] core.domain.stats_services @manoj-makkuboy 
- [x] core.domain.subscription_services @vibhor98 
- [x] core.domain.summary_services @domevit 
- [x] core.domain.user_jobs_continuous @shubha1593 
- [x] core.domain.user_services @Nalinc 
- [x] core.domain.value_generators_domain @meetsha 
- [x] core.jobs @brianrodri
- [x] core.platform.app_identity.gae_app_identity_services @ubhisat
- [x] core.platform.models @pranavsid98 
- [x] core.platform.transactions.gae_transaction_services @ubhisat
- [x] core.storage.base_model.gae_models @vojtechjelinek
- [x] core.storage.collection.gae_models @kaggis
- [x] core.storage.email.gae_models @rajan-garg
- [x] core.storage.exploration.gae_models @kirankonduru
- [x] core.storage.feedback.gae_models @naveenshukla
- [x] core.storage.file.gae_models @Ian91 
- [x] core.storage.job.gae_models @sasacocic
- [x] core.storage.statistics.gae_models @abhishekarya286
- [x] core.storage.user.gae_models @Anthony-Alridge 
- [x] core.tests.test_util_jobs @seanlip
- [x] core.tests.test_utils @vibhor98
- [x] utils @yashLadha 


Discussion:
@seanlip I would like to work in the issue.

Hi @souravsingh, do you think you could finish up #2051 first, please? Thanks! 

@seanlip I would like to work on this issue.

Hi @andromfins -- now that you've had a go at writing docstrings for a single class, would you mind picking one or two other files and doing the same thing for those? Let me know which ones you pick, so that I can mark you off against them.

Thanks!

Hi, i'm working on **core.domain.classifier_services**.

OK, thanks @andromfins! 

@seanlip Can I take a stab at other file to add docstrings?

Yep, sounds good. Could you take core.domain.html_cleaner? Thanks!

@andromfins -- are you still working on this?

  @seanlip Yes!

I would like to work on `core.domain.stats_domain`

@Arunabh98 assigned you on `core.domain.stats_domain`

Almost completed `core.domain.stats_domain`. Now working on `core.domain.stats_jobs_continuous`

hi @seanlip 
I am working on this issue.
I am writing the docstrings for /core/storage/collection/gae_models.py as i was assigned as a starting project.

@seanlip can I work on core.controllers.cron?
Yep, sounds good! I've updated the list.
@seanlip I'd like to work on core.storage.job.gae_models.
Sounds good, thanks @sasacocic! I've updated the list. 
@seanlip I'd like to work on core.platform.models. Thanks

@seanlip I'd like to work on core.domain.stats_services
Sounds good, thanks @arjunmahishi! I've assigned you. 
@seanlip I'd like to work on core.domain.summary_services
Sounds good, thanks! I've assigned you.
@seanlip Hello, i would work on core.domain.config_domain if possible.
@tvallois I have assigned you to that. Thanks
@seanlip I can do core.domain.rights_manager.py
Sounds good @fodra, I've assigned you. Thanks! 
@seanlip I would like to take _core.tests.test_util_jobs_
Sounds great, I've assigned you. Thanks @terrameijar! 
@seanlip could i work on  core.storage.statistics.gae_models?

I'd like to contribute to this, could you please assign me one of the sub tasks?
Hi @fsam95, welcome to Oppia! Could you please follow the instructions [here](https://github.com/oppia/oppia/wiki/Contributing-code-to-Oppia#setting-things-up) first?

@cosmicAsymmetry The list of tasks that are yet to be done is in the "Not started" section. Would you be up for taking a look at the corresponding files, and picking one that looks approachable? Note that test_utils has some prior work that you might be able to extend, though it's slightly unusual because the functions within it are meant mainly for supporting backend testing (and are therefore not directly user-facing). Thanks!
I've followed the instructions :). 
Thanks @fsam95! Assigned you. 
@seanlip I want to take one of the files but it looks like all the files in "Not started" section have been documented? Can you assign me to one which has not been taken? Thanks! :)
Hi @zhengxit -- actually, all those files still need work, I think, be it improving the existing docstrings, writing new docstrings for methods/functions which don't have them, or making sure that everything follows the correct style. So, please feel free to pick one of them!
(P.S. If you see a particular file in the "Not started" section that you're not sure what to do with, just ask.)
@seanlip I would like to take **core.controllers.base**

Assigned. Thanks @shaz13! 
I'm starting work on **core.jobs**.
@seanlip Please assign me an issue.I also want to contribute.
can I take #2394 Docstrings for controllers/base.py
@seanlip I am taking core.domain.stats_services
OK, thanks! Assigned you.
hey...I am working on core.domain.stats_services....I can see previous docstrings in it.So, what exactly is incomplete in this project.
Hello @arjunsuri, you can look at the previous PRs' ( alike #3448, #2459 ) to get an idea about expected format. I looked into the file [core.domain.stats_services. ](https://github.com/oppia/oppia/blob/develop/core/domain/stats_services.py) there are still few functions missing Args, Return information which you should document in your PR. If you still have any doubts feel free to ping us in the Gitter channel. 
I would like to work on `core.domain.value_generators_domain`
Sounds good, thanks @meetsha. I've assigned you! 
I would like to work on  `core.domain.user_jobs_continuous`

Sounds good, thanks @shubha1593. I've assigned you! 
I would like to be assigned core.domain.fs_domain :)
Thanks @Wert1996. I've assigned you!
@seanlip I want to take core.domain.stats_services

@arjunsuri, I've assigned you!
@kevinlee12  I was looking into core.domain.stats_services....Can you please tell me what exactly I have to do with documentation as this is my first ever contribution
To start off, I'd recommend taking a look at the other PR's like PR #3448, there's quite a lot of PR's linked so you can use those as samples of what we are looking for!
Actually...I think I am not able to understand the complete code....otherwise I could have done it by now.Can you please help me in any way so that I can understand the written code and not the docstring...so that I can write my own docstring. 
@arjunsuri Hi there! I suggest you using Sublime Text editor or something similar (VS Code, Atom) to look up the definitions throughout the codebase and what they do. If you have any particular question about a function and its use then feel free to ping us on Gitter. Thanks!

Resolving patch:
diff --git a/core/domain/value_generators_domain.py b/core/domain/value_generators_domain.py
--- a/core/domain/value_generators_domain.py
+++ b/core/domain/value_generators_domain.py
@@ -45,12 +45,23 @@ def id(self):
 
     @classmethod
     def get_html_template(cls):
+        """Returns the HTML template for the class.
+
+        Returns:
+            str. The HTML template corresponding to the class.
+        """
         return utils.get_file_contents(os.path.join(
             os.getcwd(), feconf.VALUE_GENERATORS_DIR, 'templates',
             '%s.html' % cls.__name__))
 
     @classmethod
     def get_js_template(cls):
+        """Returns the JavaScript template for the class.
+
+        Returns:
+            str. The JS template corresponding to the class.
+        """
+
         # NB: These generators should use only Angular templating. The
         # variables they have access to are generatorId, initArgs,
         # customizationArgs and objType.
@@ -67,13 +78,19 @@ def generate_value(self, *args, **kwargs):
 
 
 class Registry(object):
-    """Registry of all value generators."""
+    """Maintains a registry of all the value generators.
 
-    # Dict mapping value generator class names to their classes.
+    Attributes:
+        value_generators_dict: dict(str : BaseValueGenerator). Dictionary
+            mapping value generator class names to their classes.
+    """
     value_generators_dict = {}
 
     @classmethod
     def _refresh_registry(cls):
+        """Refreshes the dictionary mapping between generator_id and the
+        corresponding generator classes.
+        """
         cls.value_generators_dict.clear()
 
         # Assemble all generators in
@@ -108,7 +125,18 @@ def get_generator_class_by_id(cls, generator_id):
         """Gets a generator class by its id.
 
         Refreshes once if the generator is not found; subsequently, throws an
-        error."""
+        error.
+
+        Args:
+            generator_id: str. An id corresponding to a generator class.
+
+        Returns:
+            class(BaseValueGenerator). A generator class mapping to the
+                generator id given.
+
+        Raises:
+            KeyError: The given generator_id is invalid.
+        """
         if generator_id not in cls.value_generators_dict:
             cls._refresh_registry()
         return cls.value_generators_dict[generator_id]


Test patch: