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. 

Resolving patch:
diff --git a/core/jobs.py b/core/jobs.py
--- a/core/jobs.py
+++ b/core/jobs.py
@@ -1082,7 +1082,7 @@ def get_data_for_recent_jobs(recency_msec=DEFAULT_RECENCY_MSEC):
     returned.
 
     Args:
-    - recency_secs: the threshold for a recent job, in seconds.
+        recency_msec: the threshold for a recent job, in milliseconds.
     """
     recent_job_models = job_models.JobModel.get_recent_jobs(
         NUM_JOBS_IN_DASHBOARD_LIMIT, recency_msec)
diff --git a/core/storage/job/gae_models.py b/core/storage/job/gae_models.py
--- a/core/storage/job/gae_models.py
+++ b/core/storage/job/gae_models.py
@@ -40,7 +40,14 @@ class JobModel(base_models.BaseModel):
 
     @classmethod
     def get_new_id(cls, entity_name):
-        """Overwrites superclass method."""
+        """Overwrites superclass method.
+
+        Args:
+            entity_name: str. The name of the entity to create a new job id for.
+
+        Returns:
+            str. A job id.
+        """
         job_type = entity_name
         current_time_str = str(int(utils.get_current_time_in_millisecs()))
         random_int = random.randint(0, 1000)
@@ -86,6 +93,17 @@ def is_cancelable(self):
 
     @classmethod
     def get_recent_jobs(cls, limit, recency_msec):
+        """Gets at most limit jobs with respect to a time after recency_msec.
+
+        Args:
+            limit: int. A limit on the number of jobs to return.
+            recency_msec: int. The number of milliseconds earlier
+                than the current time.
+
+        Returns:
+            list(JobModel) or None. A list of at most `limit` jobs
+            that come after recency_msec time.
+        """
         earliest_time_msec = (
             utils.get_current_time_in_millisecs() - recency_msec)
         return cls.query().filter(
@@ -94,17 +112,40 @@ def get_recent_jobs(cls, limit, recency_msec):
 
     @classmethod
     def get_all_unfinished_jobs(cls, limit):
+        """Gets at most `limit` unfinished jobs.
+
+        Args:
+            limit: int. A limit on the number of jobs to return.
+
+        Returns:
+            list(JobModel) or None. A list of at most `limit` number
+            of unfinished jobs.
+        """
         return cls.query().filter(
             JobModel.status_code.IN([STATUS_CODE_QUEUED, STATUS_CODE_STARTED])
         ).order(-cls.time_queued_msec).fetch(limit)
 
     @classmethod
     def get_unfinished_jobs(cls, job_type):
+        """Gets jobs that are unfinished.
+
+        Args:
+            job_type: str. The type of jobs that may be unfinished.
+
+        Returns:
+            list(JobModel) or None. A list of all jobs that belong
+            to the given job_type.
+        """
         return cls.query().filter(cls.job_type == job_type).filter(
             JobModel.status_code.IN([STATUS_CODE_QUEUED, STATUS_CODE_STARTED]))
 
     @classmethod
     def do_unfinished_jobs_exist(cls, job_type):
+        """Checks if unfinished jobs exist.
+
+        Returns:
+            bool. True if unfinished jobs exist, otherwise false.
+        """
         return bool(cls.get_unfinished_jobs(job_type).count(limit=1))
 
 


Test patch: