removed references to deprecated python_utils file

Coding-style-guide.md

@@ -20,7 +20,6 @@ If you use [Sublime Text](http://www.sublimetext.com/), consider installing the
 ## Python
 - 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.
-- Do not use `str()` under any circumstances. Please try to use `python_utils.convert_to_bytes()` or the `b'` prefix for the strings used in webapp2\'s built-in methods or for strings used directly in NDB datastore models. If you need to cast ints/floats to strings, please use `python_utils.UNICODE()` instead. Avoid casting strings to other types of strings using str(), unicode(), etc. Also, there should be no need to prefix any string literals with b' or u', since all string literals in Python files are prefixed with `u'` by default (due to the import of unicode_literals at the top of the file).
 - 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.

Custom-Pylint-checks.md

@@ -452,7 +452,7 @@ def test_finds_hello_world_assignment(self):
         doc='Custom test')
     temp_file = tempfile.NamedTemporaryFile()
     filename = temp_file.name
-    with python_utils.open_file(filename, 'w') as tmp:
+    with open(filename, 'w') as tmp:
         tmp.write('s = "Hello, world!"')
     node.file = filename
     node.path = filename
@@ -472,7 +472,7 @@ def test_finds_hello_world_func_call(self):
         doc='Custom test')
     temp_file = tempfile.NamedTemporaryFile()
     filename = temp_file.name
-    with python_utils.open_file(filename, 'w') as tmp:
+    with open(filename, 'w') as tmp:
         tmp.write('print("Hello, world!")')
     node.file = filename
     node.path = filename
@@ -499,7 +499,7 @@ def test_finds_hello_world_assignment(self):
     temp_file = tempfile.NamedTemporaryFile()
     filename = temp_file.name
 
-    with python_utils.open_file(filename, 'w') as tmp:
+    with open(filename, 'w') as tmp:
         tmp.write("""
         s = "Hello, world!"
         print("Hello, world!")

Find-the-right-code-to-change.md

@@ -193,7 +193,7 @@ Next let's identify the backend files involved in handling updates to the user's
    +             'User experience exceeds maximum character limit: %s'
    +             % feconf.MAX_BIO_LENGTH_IN_CHARS)
    +     else:
-   +         python_utils.PRINT(
+   +         print(
    +             'DEBUG Controller received update: ' +
    +             data)
    ```
@@ -218,7 +218,7 @@ Next let's identify the backend files involved in handling updates to the user's
        """
        user_settings = get_user_settings(user_id, strict=True)
        user_settings.user_experience = user_experience
-       python_utils.PRINT(
+       print(
            'DEBUG: update_user_experience: ' + user_experience)
        _save_user_settings(user_settings)
     ```
@@ -233,7 +233,7 @@ Next let's identify the backend files involved in handling updates to the user's
                  'User experience exceeds maximum character limit: %s'
                  % feconf.MAX_BIO_LENGTH_IN_CHARS)
          else:
-   -         python_utils.PRINT(
+   -         print(
    -             'DEBUG Controller received update: ' +
    -             data)
    +         user_services.update_user_experience(self.user_id, data)
@@ -279,15 +279,15 @@ Next let's identify the backend files involved in handling updates to the user's
    First, let's add a `user_experience` argument to the constructor, assign that argument to an instance field, and update the appropriate docstrings:
 
    ```diff
-   @@ -55,6 +55,7 @@ class UserSettings(python_utils.OBJECT):
+   @@ -55,6 +55,7 @@ class UserSettings:
                 a dataURI string.
             default_dashboard: str or None. The default dashboard of the user.
             user_bio: str. User-specified biography.
    +        user_experience: str. User-specified experience description.
             subject_interests: list(str) or None. Subject interests specified by
                 the user.
             first_contribution_msec: float or None. The time in milliseconds when
-   @@ -77,7 +78,7 @@ class UserSettings(python_utils.OBJECT):
+   @@ -77,7 +78,7 @@ class UserSettings:
                 profile_picture_data_url=None, default_dashboard=None,
                 creator_dashboard_display_pref=(
                     constants.ALLOWED_CREATOR_DASHBOARD_DISPLAY_PREFS['CARD']),
@@ -296,15 +296,15 @@ Next let's identify the backend files involved in handling updates to the user's
                 preferred_language_codes=None, preferred_site_language_code=None,
                 preferred_audio_language_code=None, pin=None, display_alias=None,
                 deleted=False, created_on=None):
-   @@ -106,6 +107,7 @@ class UserSettings(python_utils.OBJECT):
+   @@ -106,6 +107,7 @@ class UserSettings:
                 creator_dashboard_display_pref: str. The creator dashboard of the
                     user.
                 user_bio: str. User-specified biography.
    +            user_experience: str. User-specified experience description.
                 subject_interests: list(str) or None. Subject interests specified by
                     the user.
                 first_contribution_msec: float or None. The time in milliseconds
-   @@ -140,6 +142,7 @@ class UserSettings(python_utils.OBJECT):
+   @@ -140,6 +142,7 @@ class UserSettings:
             self.default_dashboard = default_dashboard
             self.creator_dashboard_display_pref = creator_dashboard_display_pref
             self.user_bio = user_bio
@@ -317,7 +317,7 @@ Next let's identify the backend files involved in handling updates to the user's
    Next, we need to update the `to_dict` function to include the `user_experience` field:
 
    ```diff
-   @@ -293,6 +296,7 @@ class UserSettings(python_utils.OBJECT):
+   @@ -293,6 +296,7 @@ class UserSettings:
                 'creator_dashboard_display_pref': (
                     self.creator_dashboard_display_pref),
                 'user_bio': self.user_bio,
@@ -369,7 +369,7 @@ Now that we have the user experience field added to all the models, we can updat
          logging.error('Could not find user with id %s' % user_id)
          raise Exception('User not found.')
    + if user_settings:
-   +     python_utils.PRINT(
+   +     print(
    +         'DEBUG get_user_settings experience: ' +
    +         user_settings.user_experience)
      return user_settings
@@ -401,7 +401,7 @@ Now that we have the user experience field added to all the models, we can updat
              user_email_preferences.can_receive_subscription_email),
          'subscription_list': subscription_list
      })
-   + python_utils.PRINT(self.values)
+   + print(self.values)
      self.render_json(self.values)
    ```
 

Lint-Checks.md

@@ -45,10 +45,10 @@ We use linters to check our code for common errors or bad patterns. The Oppia li
    python -m scripts.linters.run_lint_checks --files {{file paths}}
    ```
 
-   Separate file paths with spaces. For example, to lint `scripts/start.py` and `python_utils.py`, you could run this:
+   Separate file paths with spaces. For example, to lint `scripts/start.py` and `servers.py`, you could run this:
 
    ```console
-   python -m scripts.linters.run_lint_checks --files scripts/start.py python_utils.py
+   python -m scripts.linters.run_lint_checks --files scripts/start.py servers.py
    ```
 
 4. To lint files in verbose mode, add the `--verbose` flag like this: