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Description:

permission 0.4.1

Simple and flexible permission control for Flask app.

Features

Simple: all you need to do is subclassing Rule and
Permission class.
Flexible: support rule inheritance and bitwise operations(&
and |) to build your own rules.

Installation
$ pip install permission

Rule
Rule has 3 methods which can be overrided:

base(): define base rule.
check(): determine whether this rule should be passed or not.
deny(): will be executed when check() failed.

You should always override check() and deny() while overriding
base() as needed.

Permission
Permission has 1 method which can be overrided:

rule(): define rule needed by this permission

You should always override rule().
Permission has 2 instance methods you can use in codes:

check(): call this to check rule of this permission
deny(): call this to execute codes when check() failed

Usage
First you need to define your own rules by subclassing Rule then
override check() and deny():
# rules.py
from flask import session, flash, redirect, url_for
from permission import Rule

class UserRule(Rule):
def check(self):
"""Check if there is a user signed in."""
return 'user_id' in session

def deny(self):
"""When no user signed in, redirect to signin page."""
flash('Sign in first.')
return redirect(url_for('signin'))
Then you define permissions by subclassing Permission and override
rule():
# permissions.py
from permission import Permission
from .rules import UserRule

class UserPermission(Permission):
"""Only signin user has this permission."""
def rule(self):
return UserRule()
There are 4 ways to use the UserPermission defined above:
1. Use as view decorator
from .permissions import UserPermission

@app.route('/settings')
@UserPermission()
def settings():
"""User settings page, only accessable for sign-in user."""
return render_template('settings.html')
2. Use in view codes
from .permissions import UserPermission

@app.route('/settions')
def settings():
permission = UserPermission()
if not permission.check()
return permission.deny()
return render_template('settings.html')
3. Use in view codes (using ``with`` statement)
from .permissions import UserPermission

@app.route('/settions')
def settings():
with UserPermission():
return render_template('settings.html')
Note: if you don’t raise an exception when the permission check
failed (in other words, a rule’s deny() will be called),
PermissionDeniedException will be raised in order to stop the
execution of the with-body codes. By the way, you can import this
exception as needed:
from permission import PermissionDeniedException
4. Use in Jinja2 templates
First you need to inject your defined permissions to template context:
from . import permissions

@app.context_processor
def inject_vars():
return dict(
permissions=permissions
)
then in templates:
{% if permissions.UserPermission().check() %}
<a href="{{ url_for('new') }}">New</a>
{% endif %}

Rule Inheritance
Need to say, inheritance here is not the same thing as Python class
inheritance, it’s just means you can use RuleA as the base rule of
RuleB.
We achieve this by overriding base().
Let’s say an administrator user should always be a user:
# rules.py
from flask import session, abort, flash, redirect, url_for
from permission import Rule

class UserRule(Rule):
def check(self):
return 'user_id' in session

def deny(self):
flash('Sign in first.')
return redirect(url_for('signin'))

class AdminRule(Rule):
def base(self):
return UserRule()

def check(self):
user_id = int(session['user_id'])
user = User.query.filter(User.id == user_id).first()
return user and user.is_admin

def deny(self):
abort(403)

Rule Bitwise Operations

RuleA & RuleB means it will be passed when both RuleA and RuleB
are passed.
RuleA | RuleB means it will be passed either RuleA or RuleB is
passed.

Let’s say we need to build a forum with Flask. Only the topic creator
and administrator user can edit a topic:
First define rules:
# rules.py
from flask import session, abort, flash, redirect, url_for
from permission import Rule
from .models import User, Topic

class UserRule(Rule):
def check(self):
"""Check if there is a user signed in."""
return 'user_id' in session

def deny(self):
"""When no user signed in, redirect to signin page."""
flash('Sign in first.')
return redirect(url_for('signin'))

class AdminRule(Rule):
def base(self):
return UserRule()

def check(self):
user_id = int(session['user_id'])
user = User.query.filter(User.id == user_id).first()
return user and user.is_admin

def deny(self):
abort(403)

class TopicCreatorRule(Rule):
def __init__(self, topic):
self.topic = topic
super(TopicCreatorRule, self).__init__()

def base(self):
return UserRule()

def check(self):
return topic.user_id == session['user_id']

def deny(self):
abort(403)
then define permissions:
# permissions.py
from permission import Permission

class TopicAdminPermission(Permission):
def __init__(self, topic):
self.topic = topic
super(TopicAdminPermission, self).__init__()

def rule(self):
return AdminRule() | TopicCreatorRule(self.topic)
so we can use TopicAdminPermission in edit_topic view:
from .permissions import TopicAdminPermission

@app.route('topic/<int:topic_id>/edit')
def edit_topic(topic_id):
topic = Topic.query.get_or_404(topic_id)
permission = TopicAdminPermission(topic)
if not permission.check():
return permission.deny()
...

License
MIT