- •Front Matter
- •Copyright, Trademarks, and Attributions
- •Attributions
- •Print Production
- •Contacting The Publisher
- •HTML Version and Source Code
- •Typographical Conventions
- •Author Introduction
- •Audience
- •Book Content
- •The Genesis of repoze.bfg
- •The Genesis of Pyramid
- •Thanks
- •Pyramid Introduction
- •What Makes Pyramid Unique
- •URL generation
- •Debug Toolbar
- •Debugging settings
- •Class-based and function-based views
- •Extensible templating
- •Rendered views can return dictionaries
- •Event system
- •Built-in internationalization
- •HTTP caching
- •Sessions
- •Speed
- •Exception views
- •No singletons
- •View predicates and many views per route
- •Transaction management
- •Flexible authentication and authorization
- •Traversal
- •Tweens
- •View response adapters
- •Testing
- •Support
- •Documentation
- •What Is The Pylons Project?
- •Pyramid and Other Web Frameworks
- •Installing Pyramid
- •Before You Install
- •Installing Pyramid on a UNIX System
- •Installing the virtualenv Package
- •Creating the Virtual Python Environment
- •Installing Pyramid Into the Virtual Python Environment
- •Installing Pyramid on a Windows System
- •What Gets Installed
- •Application Configuration
- •Summary
- •Creating Your First Pyramid Application
- •Hello World
- •Imports
- •View Callable Declarations
- •WSGI Application Creation
- •WSGI Application Serving
- •Conclusion
- •References
- •Creating a Pyramid Project
- •Scaffolds Included with Pyramid
- •Creating the Project
- •Installing your Newly Created Project for Development
- •Running The Tests For Your Application
- •Running The Project Application
- •Reloading Code
- •Viewing the Application
- •The Debug Toolbar
- •The Project Structure
- •The MyProject Project
- •development.ini
- •production.ini
- •MANIFEST.in
- •setup.py
- •setup.cfg
- •The myproject Package
- •__init__.py
- •views.py
- •static
- •templates/mytemplate.pt
- •tests.py
- •Modifying Package Structure
- •Using the Interactive Shell
- •What Is This pserve Thing
- •Using an Alternate WSGI Server
- •Startup
- •The Startup Process
- •Deployment Settings
- •Request Processing
- •URL Dispatch
- •High-Level Operational Overview
- •Route Pattern Syntax
- •Route Declaration Ordering
- •Route Matching
- •The Matchdict
- •The Matched Route
- •Routing Examples
- •Example 1
- •Example 2
- •Example 3
- •Matching the Root URL
- •Generating Route URLs
- •Static Routes
- •Debugging Route Matching
- •Using a Route Prefix to Compose Applications
- •Custom Route Predicates
- •Route Factories
- •Using Pyramid Security With URL Dispatch
- •Route View Callable Registration and Lookup Details
- •References
- •Views
- •View Callables
- •View Callable Responses
- •Using Special Exceptions In View Callables
- •HTTP Exceptions
- •How Pyramid Uses HTTP Exceptions
- •Custom Exception Views
- •Using a View Callable to Do an HTTP Redirect
- •Handling Form Submissions in View Callables (Unicode and Character Set Issues)
- •Alternate View Callable Argument/Calling Conventions
- •Renderers
- •Writing View Callables Which Use a Renderer
- •Built-In Renderers
- •string: String Renderer
- •json: JSON Renderer
- •JSONP Renderer
- •*.pt or *.txt: Chameleon Template Renderers
- •*.mak or *.mako: Mako Template Renderer
- •Varying Attributes of Rendered Responses
- •Deprecated Mechanism to Vary Attributes of Rendered Responses
- •Adding and Changing Renderers
- •Adding a New Renderer
- •Changing an Existing Renderer
- •Overriding A Renderer At Runtime
- •Templates
- •Using Templates Directly
- •System Values Used During Rendering
- •Chameleon ZPT Templates
- •A Sample ZPT Template
- •Using ZPT Macros in Pyramid
- •Templating with Chameleon Text Templates
- •Side Effects of Rendering a Chameleon Template
- •Debugging Templates
- •Chameleon Template Internationalization
- •Templating With Mako Templates
- •A Sample Mako Template
- •Automatically Reloading Templates
- •Available Add-On Template System Bindings
- •View Configuration
- •Mapping a Resource or URL Pattern to a View Callable
- •@view_defaults Class Decorator
- •NotFound Errors
- •Debugging View Configuration
- •Static Assets
- •Serving Static Assets
- •Generating Static Asset URLs
- •Advanced: Serving Static Assets Using a View Callable
- •Root-Relative Custom Static View (URL Dispatch Only)
- •Overriding Assets
- •The override_asset API
- •Request and Response Objects
- •Request
- •Special Attributes Added to the Request by Pyramid
- •URLs
- •Methods
- •Unicode
- •Multidict
- •Dealing With A JSON-Encoded Request Body
- •Cleaning Up After a Request
- •More Details
- •Response
- •Headers
- •Instantiating the Response
- •Exception Responses
- •More Details
- •Sessions
- •Using The Default Session Factory
- •Using a Session Object
- •Using Alternate Session Factories
- •Creating Your Own Session Factory
- •Flash Messages
- •Using the session.flash Method
- •Using the session.pop_flash Method
- •Using the session.peek_flash Method
- •Preventing Cross-Site Request Forgery Attacks
- •Using the session.get_csrf_token Method
- •Using the session.new_csrf_token Method
- •Using Events
- •An Example
- •Reloading Templates
- •Reloading Assets
- •Debugging Authorization
- •Debugging Not Found Errors
- •Debugging Route Matching
- •Preventing HTTP Caching
- •Debugging All
- •Reloading All
- •Default Locale Name
- •Including Packages
- •pyramid.includes vs. pyramid.config.Configurator.include()
- •Mako Template Render Settings
- •Mako Directories
- •Mako Module Directory
- •Mako Input Encoding
- •Mako Error Handler
- •Mako Default Filters
- •Mako Import
- •Mako Preprocessor
- •Examples
- •Understanding the Distinction Between reload_templates and reload_assets
- •Adding A Custom Setting
- •Logging
- •Sending Logging Messages
- •Filtering log messages
- •Logging Exceptions
- •PasteDeploy Configuration Files
- •PasteDeploy
- •Entry Points and PasteDeploy .ini Files
- •[DEFAULTS] Section of a PasteDeploy .ini File
- •Command-Line Pyramid
- •Displaying Matching Views for a Given URL
- •The Interactive Shell
- •Extending the Shell
- •IPython or bpython
- •Displaying All Application Routes
- •Invoking a Request
- •Writing a Script
- •Changing the Request
- •Cleanup
- •Setting Up Logging
- •Making Your Script into a Console Script
- •Internationalization and Localization
- •Creating a Translation String
- •Using The TranslationString Class
- •Using the TranslationStringFactory Class
- •Working With gettext Translation Files
- •Installing Babel and Lingua
- •Extracting Messages from Code and Templates
- •Initializing a Message Catalog File
- •Updating a Catalog File
- •Compiling a Message Catalog File
- •Using a Localizer
- •Performing a Translation
- •Performing a Pluralization
- •Obtaining the Locale Name for a Request
- •Performing Date Formatting and Currency Formatting
- •Chameleon Template Support for Translation Strings
- •Mako Pyramid I18N Support
- •Localization-Related Deployment Settings
- •Activating Translation
- •Adding a Translation Directory
- •Setting the Locale
- •Locale Negotiators
- •The Default Locale Negotiator
- •Using a Custom Locale Negotiator
- •Virtual Hosting
- •Virtual Root Support
- •Further Documentation and Examples
- •Test Set Up and Tear Down
- •What?
- •Using the Configurator and pyramid.testing APIs in Unit Tests
- •Creating Integration Tests
- •Creating Functional Tests
- •Resources
- •Location-Aware Resources
- •Generating The URL Of A Resource
- •Overriding Resource URL Generation
- •Generating the Path To a Resource
- •Finding a Resource by Path
- •Obtaining the Lineage of a Resource
- •Determining if a Resource is In The Lineage of Another Resource
- •Finding the Root Resource
- •Resources Which Implement Interfaces
- •Finding a Resource With a Class or Interface in Lineage
- •Pyramid API Functions That Act Against Resources
- •Much Ado About Traversal
- •URL Dispatch
- •Historical Refresher
- •Traversal (aka Resource Location)
- •View Lookup
- •Use Cases
- •Traversal
- •Traversal Details
- •The Resource Tree
- •The Traversal Algorithm
- •A Description of The Traversal Algorithm
- •Traversal Algorithm Examples
- •References
- •Security
- •Enabling an Authorization Policy
- •Enabling an Authorization Policy Imperatively
- •Protecting Views with Permissions
- •Setting a Default Permission
- •Assigning ACLs to your Resource Objects
- •Elements of an ACL
- •Special Principal Names
- •Special Permissions
- •Special ACEs
- •ACL Inheritance and Location-Awareness
- •Changing the Forbidden View
- •Debugging View Authorization Failures
- •Debugging Imperative Authorization Failures
- •Creating Your Own Authentication Policy
- •Creating Your Own Authorization Policy
- •Combining Traversal and URL Dispatch
- •A Review of Non-Hybrid Applications
- •URL Dispatch Only
- •Traversal Only
- •Hybrid Applications
- •The Root Object for a Route Match
- •Using *traverse In a Route Pattern
- •Using *subpath in a Route Pattern
- •Corner Cases
- •Registering a Default View for a Route That Has a view Attribute
- •Using Hooks
- •Changing the Not Found View
- •Changing the Forbidden View
- •Changing the Request Factory
- •Using The Before Render Event
- •Adding Renderer Globals (Deprecated)
- •Using Response Callbacks
- •Using Finished Callbacks
- •Changing the Traverser
- •Changing How pyramid.request.Request.resource_url() Generates a URL
- •Changing How Pyramid Treats View Responses
- •Using a View Mapper
- •Creating a Tween Factory
- •Registering an Implicit Tween Factory
- •Suggesting Implicit Tween Ordering
- •Explicit Tween Ordering
- •Displaying Tween Ordering
- •Pyramid Configuration Introspection
- •Using the Introspector
- •Introspectable Objects
- •Pyramid Introspection Categories
- •Introspection in the Toolbar
- •Disabling Introspection
- •Rules for Building An Extensible Application
- •Fundamental Plugpoints
- •Extending an Existing Application
- •Extending the Application
- •Overriding Views
- •Overriding Routes
- •Overriding Assets
- •Advanced Configuration
- •Two-Phase Configuration
- •Using config.action in a Directive
- •Adding Configuration Introspection
- •Introspectable Relationships
- •Thread Locals
- •Why and How Pyramid Uses Thread Local Variables
- •Using the Zope Component Architecture in Pyramid
- •Using the ZCA Global API in a Pyramid Application
- •Disusing the Global ZCA API
- •Enabling the ZCA Global API by Using hook_zca
- •Enabling the ZCA Global API by Using The ZCA Global Registry
- •Background
- •Design
- •Overall
- •Models
- •Views
- •Security
- •Summary
- •Installation
- •Preparation
- •Make a Project
- •Run the Tests
- •Expose Test Coverage Information
- •Start the Application
- •Visit the Application in a Browser
- •Decisions the zodb Scaffold Has Made For You
- •Basic Layout
- •Resources and Models with models.py
- •Views With views.py
- •Defining the Domain Model
- •Delete the Database
- •Edit models.py
- •Look at the Result of Our Edits to models.py
- •View the Application in a Browser
- •Defining Views
- •Declaring Dependencies in Our setup.py File
- •Adding View Functions
- •Viewing the Result of all Our Edits to views.py
- •Adding Templates
- •Viewing the Application in a Browser
- •Adding Authorization
- •Add Authentication and Authorization Policies
- •Add security.py
- •Give Our Root Resource an ACL
- •Add Login and Logout Views
- •Change Existing Views
- •Add permission Declarations to our view_config Decorators
- •Add the login.pt Template
- •Change view.pt and edit.pt
- •See Our Changes To views.py and our Templates
- •View the Application in a Browser
- •Adding Tests
- •Test the Models
- •Test the Views
- •Functional tests
- •View the results of all our edits to tests.py
- •Run the Tests
- •Distributing Your Application
- •SQLAlchemy + URL Dispatch Wiki Tutorial
- •Background
- •Design
- •Overall
- •Models
- •Views
- •Security
- •Summary
- •Installation
- •Preparation
- •Making a Project
- •Running the Tests
- •Exposing Test Coverage Information
- •Initializing the Database
- •Starting the Application
- •Decisions the alchemy Scaffold Has Made For You
- •Basic Layout
- •View Declarations via views.py
- •Content Models with models.py
- •Making Edits to models.py
- •Changing scripts/initializedb.py
- •Reinitializing the Database
- •Viewing the Application in a Browser
- •Defining Views
- •Declaring Dependencies in Our setup.py File
- •Running setup.py develop
- •Changing the views.py File
- •Adding Templates
- •Adding Routes to __init__.py
- •Viewing the Application in a Browser
- •Adding Authorization
- •Adding A Root Factory
- •Add an Authorization Policy and an Authentication Policy
- •Adding an authentication policy callback
- •Adding Login and Logout Views
- •Changing Existing Views
- •Adding the login.pt Template
- •Seeing Our Changes To views.py and our Templates
- •Viewing the Application in a Browser
- •Adding Tests
- •Testing the Models
- •Testing the Views
- •Functional tests
- •Viewing the results of all our edits to tests.py
- •Running the Tests
- •Distributing Your Application
- •Converting a repoze.bfg Application to Pyramid
- •Running a Pyramid Application under mod_wsgi
- •pyramid.authorization
- •pyramid.authentication
- •Authentication Policies
- •Helper Classes
- •pyramid.chameleon_text
- •pyramid.chameleon_zpt
- •pyramid.config
- •pyramid.events
- •Functions
- •Event Types
- •pyramid.exceptions
- •pyramid.httpexceptions
- •HTTP Exceptions
- •pyramid.i18n
- •pyramid.interfaces
- •Event-Related Interfaces
- •Other Interfaces
- •pyramid.location
- •pyramid.paster
- •pyramid.registry
- •pyramid.renderers
- •pyramid.request
- •pyramid.response
- •Functions
- •pyramid.scripting
- •pyramid.security
- •Authentication API Functions
- •Authorization API Functions
- •Constants
- •Return Values
- •pyramid.settings
- •pyramid.testing
- •pyramid.threadlocal
- •pyramid.traversal
- •pyramid.url
- •pyramid.view
- •pyramid.wsgi
- •Glossary
CHAPTER
THIRTYFOUR
THREAD LOCALS
A thread local variable is a variable that appears to be a “global” variable to an application which uses it. However, unlike a true global variable, one thread or process serving the application may receive a different value than another thread or process when that variable is “thread local”.
When a request is processed, Pyramid makes two thread local variables available to the application: a “registry” and a “request”.
34.1 Why and How Pyramid Uses Thread Local Variables
How are thread locals beneficial to Pyramid and application developers who use Pyramid? Well, usually they’re decidedly not. Using a global or a thread local variable in any application usually makes it a lot harder to understand for a casual reader. Use of a thread local or a global is usually just a way to avoid passing some value around between functions, which is itself usually a very bad idea, at least if code readability counts as an important concern.
For historical reasons, however, thread local variables are indeed consulted by various Pyramid API functions. For example, the implementation of the pyramid.security function named authenticated_userid() retrieves the thread local application registry as a matter of course to find an authentication policy. It uses the pyramid.threadlocal.get_current_registry() function to retrieve the application registry, from which it looks up the authentication policy; it then uses the authentication policy to retrieve the authenticated user id. This is how Pyramid allows arbitrary authentication policies to be “plugged in”.
When they need to do so, Pyramid internals use two API functions to retrieve the request and application registry: get_current_request() and get_current_registry(). The former returns the
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“current” request; the latter returns the “current” registry. Both get_current_* functions retrieve an object from a thread-local data structure. These API functions are documented in pyramid.threadlocal.
These values are thread locals rather than true globals because one Python process may be handling multiple simultaneous requests or even multiple Pyramid applications. If they were true globals, Pyramid could not handle multiple simultaneous requests or allow more than one Pyramid application instance to exist in a single Python process.
Because one Pyramid application is permitted to call another Pyramid application from its own view code (perhaps as a WSGI app with help from the pyramid.wsgi.wsgiapp2() decorator), these variables are managed in a stack during normal system operations. The stack instance itself is a threading.local.
During normal operations, the thread locals stack is managed by a Router object. At the beginning of a request, the Router pushes the application’s registry and the request on to the stack. At the end of a request, the stack is popped. The topmost request and registry on the stack are considered “current”. Therefore, when the system is operating normally, the very definition of “current” is defined entirely by the behavior of a pyramid Router.
However, during unit testing, no Router code is ever invoked, and the definition of “current” is defined by the boundary between calls to the pyramid.config.Configurator.begin() and pyramid.config.Configurator.end() methods (or between calls to the pyramid.testing.setUp() and pyramid.testing.tearDown() functions). These functions push and pop the threadlocal stack when the system is under test. See Test Set Up and Tear Down for the definitions of these functions.
Scripts which use Pyramid machinery but never actually start a WSGI server or receive requests via HTTP such as scripts which use the pyramid.scripting API will never cause any Router code to be executed. However, the pyramid.scripting APIs also push some values on to the thread locals stack as a matter of course. Such scripts should expect the get_current_request() function to always return None, and should expect the get_current_registry() function to return exactly the same application registry for every request.
34.2 Why You Shouldn’t Abuse Thread Locals
You probably should almost never use the get_current_request() or get_current_registry() functions, except perhaps in tests. In particular, it’s almost always a mistake to use get_current_request or get_current_registry in application code because its usage makes it possible to write code that can be neither easily tested nor scripted. Inappropriate usage is defined as follows:
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34.2.WHY YOU SHOULDN’T ABUSE THREAD LOCALS
•get_current_request should never be called within the body of a view callable, or within code called by a view callable. View callables already have access to the request (it’s passed in to each as request).
•get_current_request should never be called in resource code. If a resource needs access to the request, it should be passed the request by a view callable.
•get_current_request function should never be called because it’s “easier” or “more elegant” to think about calling it than to pass a request through a series of function calls when creating some API design. Your application should instead almost certainly pass data derived from the request around rather than relying on being able to call this function to obtain the request in places that actually have no business knowing about it. Parameters are meant to be passed around as function arguments, this is why they exist. Don’t try to “save typing” or create “nicer APIs” by using this function in the place where a request is required; this will only lead to sadness later.
•Neither get_current_request nor get_current_registry should ever be called within application-specific forks of third-party library code. The library you’ve forked almost certainly has nothing to do with Pyramid, and making it dependent on Pyramid (rather than making your pyramid application depend upon it) means you’re forming a dependency in the wrong direction.
Use of the get_current_request() function in application code is still useful in very limited circumstances. As a rule of thumb, usage of get_current_request is useful within code which is meant to eventually be removed. For instance, you may find yourself wanting to deprecate some API that expects to be passed a request object in favor of one that does not expect to be passed a request object. But you need to keep implementations of the old API working for some period of time while you deprecate the older API. So you write a “facade” implementation of the new API which calls into the code which implements the older API. Since the new API does not require the request, your facade implementation doesn’t have local access to the request when it needs to pass it into the older API implementation. After some period of time, the older implementation code is disused and the hack that uses get_current_request is removed. This would be an appropriate place to use the get_current_request.
Use of the get_current_registry() function should be limited to testing scenarios. The registry made current by use of the pyramid.config.Configurator.begin() method during a test (or via pyramid.testing.setUp()) when you do not pass one in is available to you via this API.
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