Python decorators allow you to modify a function.
Consider the following example:
def override(func):
def incr():
return func() + 1
return incr
@override
def one():
return 1
print(one()) # prints 2
In the above example we first define a function override, which takes in a function as an argument and then returns a function that returns the return value of the original arugment plus 1. We then use this function as a decorator on the function one. Originally one would have returned 1, but now it has been overridden and hence will return 2 instead.
Flask is a Python-based web microframework that automates the process of building simple web apps.
Typical Flask applications are written in a file called application.py. You can think of Flask like a traffic cop - It listens to incoming requests from clients and then acts appropriately.
A simple Flask app might look like this:
from flask import Flask
app = Flask(__name__)
@app.route("/")
def index():
return "You are at the index!"
@app.route("/sample")
def sample():
return "You have reached the sample page!"
In this example we first import flask, then make a new app and finally define two routes. To define the route we use the @app.route() decorator. A route specifies what should be done when the user visits the app at a certain index. In the above example we defined two routes: / and /sample. If this app was running on the domain http://www.myapp.com then now when the user would go to http://www.myapp.com/ then the user would see "You are at the index!". If the user would visit http://www.myapp.com/sample, then the user would see "You have reached the sample page!"
For this pset, the distribution code will come with the decorator @login-required, which you can use to restrict functions to users who have logged in.
Jinja is a python inspired templating language. It allows you to make .html files dynamic, by allowing jinja to dynamically add parts to the page. With Jinja you would usually have a file called layout.html, which then gets extended with different blocks depending on which page the user is on.
SQL is programming language which is used for managing and manipulating data in relation databases.
In this pset you will use a SQLite database. SQLlite databases are stored in a .db file. In order to insert, delete or modify the data in the database you will use SQL queries.
These are the 4 basic queries you should be comfortable with:
Update is used for changing already existing data in the database.
Example:
UPDATE table SET col1 = val1, col2 = val2, ... # update table, changing values in particular columns
UPDATE table SET col1 = val1 WHERE identifier = "name" # update table, changing col1 to val1 where "name" equals "identifier"
Insert into is used to insert certain values into a table.
Example:
INSERT INTO table VALUES values # insert into table the row of values
INSERT INTO table (col1, col2) VALUES (val1, val2) # insert into table under columns col1 & col2, val1 & val2
Select is used for retrieving data from the database.
Example:
SELECT col FROM table WHERE col = "identifier" # select a column from table to compare/ view
SELECT * FROM table # select all columns from a table
Delete is used to delete exising data from the database
Example:
DELETE FROM table WHERE col = "identifier" # delete a row from table
To execute a SQL query in Flask you can used the provided db.execute() function.
To manipulate a database directly (this will come in handy when setting your database up) you will use phpliteadmin. To run phpliteadmin run the following command in the IDE, substituting mydatabase.db for the name of your database file:
$ phpliteadmin mydatabase.db