Comparison with other Web Frameworks

We hear you ask:

There are a million Python web frameworks out there. How does Morepath compare?

If you’re already familiar with another web framework, it’s useful to learn how Morepath is the same and how it is different, as that helps you understand it more quickly. So we go into some of this here.

Our ability to compare Morepath to other web frameworks is limited by our familiarity with them, and also by their aforementioned large quantity. But we’ll try. Feel free to pitch in new comparisons, or tell us where we get it wrong!

You may also want to read the Design Notes document.


Morepath aims to be foundational. All web applications are different. Some are simple. Some, like CMSes, are like frameworks themselves. It’s likely that some of you will need to build your own frameworky things on top of Morepath. Morepath doesn’t get in your way. Morepath isn’t there to be hidden away under another framework though - these extensions still look like Morepath. The orientation towards being foundational makes Morepath more like Pyramid, or perhaps Flask, than like Django.

Morepath aims to have a small core. It isn’t full stack; it’s a microframework. It should be easy to pick up. This makes it similar to other microframeworks like Flask or CherryPy, but different from Django and Zope, which offer a lot of features.

Morepath is opinionated. There is only one way to do routing and one way to do configuration. This makes it like a lot of web frameworks, but unlike Pyramid, which takes more of a toolkit approach where a lot of choices are made available.

Morepath is a routing framework, but it’s model-centric. Models have URLs. This makes it like a URL traversal framework like Zope or Grok, and also like Pyramid when traversal is in use. It makes it unlike other routing frameworks like Django or Flask, which have less awareness of models.

Paradoxically enough one thing Morepath is opinionated about is flexibility, as that’s part of its mission to be a good foundation. That’s what its configuration and generic function systems are all about. Want to change behavior? You can override everything. Even core behavior of Morepath can be changed by overriding its generic functions. This makes Morepath like Zope, and especially like Pyramid, but less like Django or Flask.


Morepath is a routing web framework, like Django and Flask and a lot of others. This is a common way to use Pyramid too (the other is traversal). This is also called URL mapping or dispatching. Morepath is to our knowledge, unique in that the routes don’t directly go to views, but go through models first.

Morepath’s route syntax is very similar to Pyramid’s, i.e. /hello/{name}. Flask is also similar. It’s unlike Django’s regular expressions. Morepath works at a higher level than that deliberately, as that makes it possible to disambiguate similar routes.

This separation of model and view lookup helps in code organisation, as it allows you to separate the code that organises the URL space from the code that implements your actual views.


Because it routes to models, Morepath allows you to ask for the URL of a model instance, like this:

That is an easier and less brittle way to make links than having to name your routes explicitly. Morepath pushes link generation quite far: it can construct links with paths and URL parameters automatically.

Morepath shares the property of model-based links with traversal based web frameworks like Zope and Grok, and also Pyramid in non-routing traversal mode. Uniquely among them Morepath does route, not traverse.

For more: Paths and Linking.

View lookup

Morepath uses a separate view lookup system. The name of the view is determined from the last step of the path being routed to. With this URL path for instance:


the /edit bit indicates the name of the view to look up for the document model.

If no view step is supplied, the default view is looked up:


This is like modern Zope works, and like how the Plone CMS works. It’s also like Grok. It’s like Pyramid if it’s used with traversal instead of routing. Overall there’s a strong Zope heritage going on, as all these systems are derived from Zope in one way or another. Morepath is unique in that it combines routing with view lookup.

This decoupling of views from models helps with expressivity, as it lets you write reusable, generic views, and code organisation as mentioned before.

For more: Views.


Morepath is a WSGI-based framework, like Flask or Pyramid. It’s natively WSGI, unlike Django, which while WSGI is supported also has its own way of doing middleware.

A Morepath app is a standard WSGI app. You can plug it into a WSGI compliant web server like Apache or Nginx or gunicorn. You can also combine Morepath with WSGI components, such as for instance the Fanstatic static resource framework.


Morepath has a permission framework built-in: it knows about authentication and lets you plug in authenticators, you can protect views with permissions and plug in code that tells Morepath what permissions someone has for which models. It’s small but powerful in what it lets you do.

This is unlike most other micro-frameworks like Flask, Bottle, CherryPy or It’s like Zope, Grok and Pyramid, and has learned from them, though Morepath’s system is more streamlined.

For more you can check out this blog entry. (It will be integrated in this documentation later).

Explicit request

Some frameworks, like Flask and Bottle, have a magic request global that you can import. But request isn’t really a global, it’s a variable, and in Morepath it’s a variable that’s passed into view functions explicitly. This makes Morepath more similar to Pyramid or Django.

Testability and Global state

Developers that care about writing testable code try to avoid global state, in particular mutable global state, as it can make testing harder. If the framework is required to be in a certain global state before the code under test can be run, it becomes harder to test that code, as you need to know first what global state to manipulate.

Globals can also be a problem when multiple threads try to write the global at the same time. Web frameworks avoid this by using thread locals. Confusingly enough these locals are globals, but they’re isolated from other threads.

Morepath the framework does not require any global state. Of course Morepath’s app are module globals, but they’re not used that way once Morepath’s configuration is loaded and Morepath starts to handle requests. Morepath’s framework code passes the app along as a variable (or attribute of a variable, such as the request) just like everything else.

Morepath is built on the Reg generic function library. Implementations of generic functions can be plugged in separately per Morepath app: each app is a registry. When you call a generic function Reg needs to know what registry to use to look it up. You can make this completely explicit by using a special lookup argument:

some_generic_function(doc, 3, lookup=app.lookup())

That’s all right in framework code, but doing that all the time is not very pretty in application code. For convenience, Morepath therefore sets up the current lookup implicitly as thread local state. Then you can simply write this:

some_generic_function(doc, 3)

Flask is quite happy to use global state (with thread locals) to have a request that you can import. Pyramid is generally careful to avoid global state, but does allow using thread local state to get access to the current registry in some cases.

Summary: Morepath does not require any global state, but allows the current lookup to be set up as such for convenience.

No default database

Morepath has no default database integration. This is like Flask and Bottle and Pyramid, but unlike Zope or Django, which have assumptions about the database baked in (ZODB and Django ORM respectively).

You can plug in your own database, or even have no database at all. You could use SQLAlchemy, or the ZODB. Morepath lets you treat anything as models. We’re not against writing examples or extensions that help you do this, though we haven’t done so yet. Contribute!

No template language

Some micro-frameworks like Flask and Bottle and have template languages built-in, some, like CherryPy and the Werkzeug toolkit, don’t. Pyramid doesn’t have built-in support either, but has standard plugins for the Chameleon and Mako template languages.

Morepath aims to be a good fit for modern, client-side web applications written in JavaScript. So we’ve focused on making it easy to send anything to the client, especially JSON. If templating is used for such applications, it’s done on the client, in the web browser, not on the server.

We’re planning on letting you plug in server-side template languages as they’re sometimes useful, but we haven’t done so yet. Feel free to contribute!

For now, you can plug in something yourself. CherryPy has a good document on how to do that with CherryPy, and it’d look very similar with Morepath.

Code configuration

Most Python web frameworks don’t have an explicit code configuration system. With “code configuration” I mean expressing things like “this function handles this route”, “this view works for this model”, and “this is the current authentication system”. It also includes extension and overrides, such as “here is an additional route”, “use this function to handle this route instead of what the core said”.

If a web framework doesn’t deal with code configuration explicitly, an implicit code configuration tends to grow. There is one way to set up routes, another way to declare models, another way to do generic views, yet another way to configure the permission system, and so on. Each system works differently and uses a different API. Config files, metaclasses and import-time side effects may all be involved.

On top of this, if the framework wants to allow reuse, extension and overrides the APIs tends to grow even more distinct with specialised use cases, or yet more new APIs are grown.

Django is an example where configuration gained lots of knobs and buttons; another example is the original Zope.

Microframeworks aim for simplicity so don’t suffer from this so much, though probably at the cost of some flexibility. You can still observe this kind of evolution in Flask’s pluggable views subsystem, though, for instance.

To deal with this problem in an explicit way the Zope project pioneered a component configuration mechanism. By having a universal mechanism in which code is configured, the configuration API becomes general and allows extension and override in a general manner as well. Zope uses XML files for this.

The Grok project tried to put a friendlier face on the rather verbose configuration system of Zope. Pyramid refined Grok’s approach further. It offers a range of options for configuration: explicit calls in Python code, decorators, and an extension that uses Zope-style XML.

In order to do its decorator based configuration, the Pyramid project created the Venusian python library. This is in turn a reimagined version of the Martian python library created by the Grok project.

Morepath has a new configuration system that is based around decorators (using Venusian) attached to application objects. These application objects can extend other ones. This way it supports a range sophisticated extension and override use cases in a general way.

Components and Generic functions

The Zope project made the term “zope component architecture” (ZCA) (in)famous in the Python world. Does it sound impressive, suggesting flexibility and reusability? Or does it sound scary, overengineered, RequestProcessorFactoryFactory-like? Are you intimidated by it? We can’t blame you.

At its core the ZCA is really a system to add functionality to objects from the outside, without having to change their classes. It helps when you need to build extensible applications and reusable generic functionality. Under the hood, it’s just a fancy registry that knows about inheritance. Its a really powerful system to help build more complicated applications and frameworks. It’s used by Zope, Grok and Pyramid.

Morepath uses something else: a library called Reg. This is a new, reimagined, streamlined implementation of the idea of the ZCA.

The underlying registration APIs of the ZCA is rather involved, with quite a few special cases. Reg has a simpler, more general registration API that is flexible enough to fulfill a range of use cases.

Finally what makes the Zope component architecture rather involved to use is its reliance on interfaces. An interface is a special kind of object introduced by the Zope component architecture that is used to describe the API of objects. It’s like an abstract base class.

If you want to look up things in a ZCA component registry the ZCA requires you to look up an interface. This requires you to write interfaces for everything you want to be able to look up. The interface-based way to do lookups also looks rather odd to the average Python developer: it’s not considered to be very Pythonic. To mitigate the last problem Pyramid creates simple function-based APIs on top of the underlying interfaces.

Morepath by using Reg does away with interfaces altogether – instead it uses generic functions. The simple function-based APIs are what is pluggable; there is no need to deal with interfaces anymore, but the system retains the power. Morepath is simple functions all the way down.