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Get ahead

  • Activate your smiles virtualenv
  • Open smiles/ in your editor.
  • Open your terminal and navigate to the smiles/ directory.

GDI logo

Intermediate Python

Class 4

Client Server Overview

Review

  • What are some ways the client communicates information to the server?
  • What are some ways the server communicates information to the client?

Path variables

Passing information in URLs

/hello_path/Casey/

Hello Casey

Path variables

Add this to main/urls.py

# main/urls.py

urlpatterns = [
    # ...
    path('hello_path/<name>/', views.hello_path),
    # ...
]

Path variables

Path variables get passed as arguments to view functions.

# main/views.py

def hello_path(request, name):
    return render(request, 'hello.html', context={'name': name})

Then visit http://localhost:8000/hello_path/Casey/

http://localhost:8000/hello_path/Casey/

Hello Casey

What if there's no <name> in the URL?

The desired behavior:

/hello_path/

Hello World

Let's develop it

/hello_path/

Hello World

Let's develop it

Add a path in main/urls.py to hook up hello_path/ to the hello_path view.

Watch out! The urlpatterns list is ordered by precedence. In other words, earlier items in the list will match before later items.

# main/urls.py

urlpatterns = [
    # ...
    path('hello_path/', views.hello_path),
    path('hello_path/<name>/', views.hello_path),
    # ...
]

/hello_path/

Hello World broken

To fix this we need to learn about default arguments.

# main/views.py

def hello_path(request, name):
    return render(request, 'hello.html', context={'name': name})

Default arguments

Default arguments are optional.

def greet(name, time='morning'):
    return 'Good ' + time + ', ' + name

greet('Quinn')  # Good morning, Quinn
greet('Quinn', 'afternoon')  # Good afternoon, Quinn
greet('Quinn', time='night')  # Good night, Quinn

Add 'World' as the default argument for name.

def hello_path(request, name='World'):
    return render(request, 'hello.html', context={'name': name})

/hello_path/

Hello World

Testing

Writing code to save time

def yo(name):
    return 'Yo ' + name

def test_yo():
    assert greet('Casey')  == 'Yo Casey'
    assert greet('Henrique') == 'Yo Henrique'

Run the tests in tests/test_coin.py.

pytest tests/test_coin.py

Test failures

Fix the test_flip test.

# tests/test_coin.py

def test_flip():
    result = coin.flip()
    assert result in ['H', 'T']

Then rerun the tests.

pytest tests/test_coin.py

Tip: Use the up arrow to get the previous command in your terminal.

One passing

Test-driven development

Test-driven development

"Red-Green-Refactor"

  • Write the test first and watch it fail.
  • Write the code to make the test pass.
  • Improve the code (refactor).

Let's develop it

Open tests/test_coin.py.

flip_loaded() will always return 'H'.

Write an assertion for test_flip_loaded().

Let's develop it

# tests/test_coin.py

def test_flip_loaded():
    assert coin.flip_loaded() == 'H'

Run the tests.

pytest tests/test_coin.py

Failure is expected.

One passing

Now fix flip_loaded().

# main/coins.py
# ...

def flip_loaded():
    return 'H'

Run the tests.

pytest tests/test_coin.py

All green!

Hello Casey

The smiles app

Putting it all together

The smiles app

Build an app that allows the user to "say" things (send input) to a character. The app display's the character's face based on the sentiment of the user's input.

The smiles app

A character has 5 "moods" which are associated with a face and a color.

  • Very negative, :'-( , dark-red
  • Slightly negative, :-( , red
  • Neutral, :-| , lightest-blue
  • Slightly positive, :-) , washed-green
  • Very positive, :-D , green

:-|

First step: Design a character. Let's start with the Classic character.

Classic

Run the tests.

pytest tests/test_classic.py

Classic test failures

These tests will serve as a guide.

Let's develop it

get_face() has already been implemented.

Now implement get_color() to make test_get_color() pass.

Hint: get_color() should look very similar to get_face().

Let's develop it

Implement get_color().

  • Very negative, :'-( , dark-red
  • Slightly negative, :-( , red
  • Neutral, :-| , lightest-blue
  • Slightly positive, :-) , washed-green
  • Very positive, :-D , green

Checkpoint

pytest tests/test_classic.py

Classic test failures

Next let's implement listen(text).

We'll use the TextBlob package to compute the sentiment of text.

Using TextBlob

"Sentiment polarity" measures the positivity/negativity of text.

Here's how to get it with TextBlob

from textblob import TextBlob
good_blob = TextBlob('good day!')
good_blob.sentiment.polarity  # 0.875
bad_blob = TextBlob('bad day!')
bad_blob.sentiment.polarity  # -0.875

Let's develop it

The listen(text) method should change the character's mood to the sentiment polarity of text. If text is None or '' , reset the mood to 0.0.

Here's the start:

def listen(self, text):
    # If text is empty, reset mood to 0
    if not text:
        self.mood = 0.0

Use TextBlob to compute sentiment polarity.

from textblob import TextBlob
good_blob = TextBlob('good day!')
good_blob.sentiment.polarity  # 0.875
bad_blob = TextBlob('bad day!')
bad_blob.sentiment.polarity  # -0.875

Checkpoint

pytest tests/test_classic.py

Classic test failures

If you get ahead, try implementing Bear or Bird. Run pytest tests/test_more_characters.py to test them.

Let's develop it

  • Run your server with python manage.py runserver and go to http://localhost:8000 in your browser
  • Edit main/urls.py to hook up the root ('') and '<character_id>/' to the character_page view.
  • Edit templates/character.html to display the face in the right place.
{# templates/character.html #}

<h1 class="f-6 tc sans-serif">
  {{ face }}
</h1>
# main/urls.py

urlpatterns = [
    # ...
    path('', views.character_page),
    path('<character_id>/', views.character_page),
]

Now visit http://localhost:8000/ or http://localhost:8000/classic/

Smiles v1

Let's develop it

Now implement the full Bear class. It should have the same behavior as Classic except with different faces.

Run the following tests.

pytest tests/test_more_characters.py

Tip: You'll need to open another terminal window in order to run your tests.

Checkpoint

Character inheritance

Let's develop it

  • In templates/character.html, uncomment the link to /bear/.
{# TODO: Uncomment these after you've implemented Bear and Bird #}
<a class="link grow black-80 hover-blue    f6 f5-ns dib mr3" href="/bear/" title="About">Bear</a>
  • Edit main/views.py to use the Bear class when bear/ is passed in the URL.

Refactoring!

Refactoring

Classic and Bear have a lot of the same behavior. How can we reduce the duplicated code?

Character inheritance

Let's develop it

Implement a Character class from which Classic and Bear both inherit.

Character inheritance

Let's develop it

Hint: Use class variables to store the faces.

class Character:
    # ...
    def get_face(self):
        if self.mood < -0.5:  # very negative
            return self.very_negative
        # ...

class Classic(Character):
    very_negative = ":'-("
    slightly_negative = ':-('
    # ...

You made it!

Before you close your terminal, don't forget to shut down your development server using ctrl-c.

More practice

Implement Bird and hook it up to /bird/.

More practice

Read the character_page view. Can you understand its logic?

More practice

Learn about Python's @property syntax and refactor get_face() and get_color as properties.

Don't forget to change the tests!

What next?