Routing, Traversal and URL Dispatch with Pyramid

Talk at Pyramid London, May 7th 2013 looking at the basics of routing with Pyramid.

Transcript

1. Routing,
   Traversal & URL
   Dispatch
   Pyramid London // James Cooke
   

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2. The Pyramid Router
   ● Created when you start a Pyramid app.
   ● From the glossary:
   The router intercepts requests, invokes
   traversal and/or URL dispatch, calls view
   functions, and returns responses to the
   WSGI server on behalf of your Pyramid
   application.
   

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3. PyramidPress Example
   ● Home page - Show a list of our users.
   ● User view - web visitor looks at a member's
   blog. e.g. for Bob, his page is:
   /bob
   ● Post view - web visitor looks at a member's
   single post. e.g. for Bob's motorbike page:
   /bob/motorbikes
   

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4. URL Dispatch mode
   Matches route patterns returns a matchdict.
   ● User view route
   ○ Route pattern = '/{username}'
   ○ Matches '/bob'
   ○ Returns {'username': u'bob'}
   ● Page view route
   ○ Route pattern = '/{username}/{page_title}'
   ○ Matches '/bob/motors'
   ○ Returns
   {'username':u'bob', 'page_title':
   u'motors'}
   

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5. URL Dispatch summary
   ● Simplest way to get started with Pyramid.
   ● Covers most use cases.
   ● Familiar to users experienced with other
   platforms.
   

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6. Traversal Algorithm
   ● Resources of two types:
   ○ Container - dictionary-like, has __getitem__.
   ○ Leaf.
   ● Walk the URL until:
   ○ Path is exhausted.
   ○ KeyError is raised.
   ○ Non-final element has no __getitem__.
   ○ Path element starts with @@.
   

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7. Traversal Example
   ● With '/'
   ● Pyramid Router makes []
   ● Returns root_resource.
   ● Path exhausted.
   ● Returns Root in response['context']
   ● View lookup now finds suitable view for Root
   context and calls it.
   

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8. Traversal Example
   ● With '/bob/motors'
   ● Pyramid Router makes [u'bob', u'motors']
   ● Calls root_resource.__getitem__(u'bob')
   ○ Which returns
   ● Calls bob.__getitem__(u'motors')
   ○ Which returns
   ● Path exhausted.
   ● Returns Motors page in response['context']
   ● View lookup again goes to work.
   

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9. Traversal Caution
   ● URL Encode & Decode implications.
   ● Test your tree.
   ● URL generation can be 'odd'.
   ● Resource / view collision.
   

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10. Hybrid Applications
    ● Play with Traversal in a safe way.
    ● Routes like:
    config.add_route('user', '/user/*traverse')
    config.add_route('user_page',
    '/user/{page}/*traverse')
    ● More URL Dispatch than Traversal.
    

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11. Traversal Summary
    ● More flexibility that URL Dispatch.
    ● Paid for with complexity.
    ● Check the docs for 'corner cases'.
    

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12. Thanks for listening
    All code is on GitHub:
    github.com/jamescooke/pyramid-london-talk
    Find me on Twitter: @jamesfublo
    Ask me questions? I'll do my best to answer :D
    

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