“ Using  Grok to Walk Like a Duck” The Zope 3 Component Architecture Brandon Craig Rhodes Plone Conference 2008, Washingto...
How many methods does a Plone ATFolder have?
Contributors CreationDate Creator Creators DELETE Date Description EffectiveDate ExpirationDate Format HEAD Identifer Iden...
Contributors CreationDate Creator Creators DELETE Date Description EffectiveDate ExpirationDate Format HEAD Identifer Iden...
Both Zope 2 and Plone solve problems by piling more and more methods on an object
Zope 3 does something different Zope 3 uses Adapters
What are adapters? Let's talk programming.
Many programming languages use  static  typing
float half(int n) { return n / 2.0; }
float  half( int  n) { return n / 2.0; }
Python typing is  dynamic
def half(n): return n / 2.0
You don't worry about whether an object is of the right type
You simply try using it
“ Duck Typing” (Alex Martelli)
“ Duck Typing” Walks like a duck? Quacks like a duck? It's a duck!
def half(n): return n / 2.0
def half(n): return n / 2.0 (Is  n  willing  to be divided by two? Then it's number-ish enough for us!)
Now, imagine...
Imagine a wonderful duck-processing library to which you want to pass an object
But... The object you want to pass  isn't  a duck?
What if it  doesn't already quack?
What if it bears not the least resemblance to a duck!?
Example!
You have a “Message” object from the Python “email” module
>>>  from email import message_from_file >>>  e = message_from_file(open('msg.txt')) >>>  print e <email.message.Message i...
multipart/mixed text/plain multipart/alternative text/plain text/html image/jpeg Messages can be recursive
Imagine that we are writing a Plone email browsing system
And we want to show the parts in a TreeWidget
multipart/mixed
multipart/mixed text/plain multipart/alternative image/jpeg
multipart/mixed text/plain multipart/alternative text/plain text/html image/jpeg
The Tree widget operates on any object with: method   name()  - returns name under which this tree node should be displaye...
How can we add these behaviors to our Message?
(How can we make an object which is  not  a duck behave like a duck?)
1. Subclassing
Create a “TreeMessage” class that inherits from the “Message” class...
class  TreeMessage ( Message ): def  name (self): return self.get_content_type() def  children (self): if not self.is_mult...
What will the test suite look like?
Remember: “ Untested code  is broken code” —  Philipp von Weitershausen, Martin Aspeli
Your test suite must instantiate a “TreeMessage” and verify its tree-like behavior...
txt =  “”” From: persephone@gmail.com To: brandon@rhodesmill.org Subject: what an article! Did you read Arts & Letters Dai...
We were lucky!
Our test can cheaply instantiate Messages.
txt =  “”” From: persephone@gmail.com To: brandon@rhodesmill.org Subject: what an article! Did you read Arts & Letters Dai...
What if we were subclassing an LDAP connector?! We'd need an LDAP server just to run unit tests!
We were lucky (#2)!
The “message_from_string()” method let us specify an alternate factory!
txt =  “”” From: persephone@gmail.com To: brandon@rhodesmill.org Subject: what an article! Did you read Arts & Letters Dai...
Final note:  we have just broken the “Message” class's behavior!
Python library manual 7.10.1 defines “Message”: __len__(): Return the total number of headers, including duplicates.
>>> t =  “”” From: persephone@gmail.com To: brandon@rhodesmill.org Subject: what an article! Did you read Arts & Letters D...
So how does subclassing score?
No harm to base class
No harm to base class Cannot test in isolation
No harm to base class Need control of factory Cannot test in isolation
No harm to base class Breaks if names collide Need control of factory Cannot test in isolation
No harm to base class Breaks if names collide Need control of factory Cannot test in isolation Subclassing:  D
2. Using a mixin
Create a “TreeMessage” class that inherits from both “Message” and a “Mixin”...
class  Mixin (object): def  name (self): return self.get_content_type() def  children (self): if not self.is_multipart(): ...
Your test suite can then inherit from a fake, mocked-up “message”...
class  FakeMessage ( Mixin ): def  get_content_type (self): return 'text/plain' def  is_multipart (self): return False def...
How does a mixin rate?
No harm to base class
No harm to base class Can test mixin by itself
No harm to base class Need control of factory Can test mixin by itself
No harm to base class Breaks if names collide Need control of factory Can test mixin by itself
No harm to base class Breaks if names collide Need control of factory Can test mixin by itself Mixin:  C
3. Monkey patching
To “monkey patch” a class, you add or change its methods dynamically...
def  name (self): return self.get_content_type() def  children (self): if not self.is_multipart(): return [] return [  Mes...
Is this desirable?
Don't care about factory
Changes class itself Don't care about factory
Changes class itself Broken by collisions Don't care about factory
Changes class itself Broken by collisions Don't care about factory Patches fight each other
Changes class itself Broken by collisions Don't care about factory Ruby people do this Patches fight each other
Changes class itself Broken by collisions Don't care about factory Ruby people do this Monkey patching:  F Patches fight e...
4. Adapter
Touted in the Gang of Four book (1994)
Idea: provide “Tree” functions through an entirely separate object Message  MessageTreeAdapter get_content_type ()  name (...
class  MessageTreeAdapter (object): def  __init__ (self, message): self. m  = message def  name (self): return self. m .ge...
How does wrapping look in your code?
Message object Adapted object IMAP library (or whatever) returns a Message “msg” TreeWidget tw = TreeWidget(MessageTreeAda...
Test suite can try adapting a mock-up object
class  FakeMessage (object): def  get_content_type (self): return 'text/plain' def  is_multipart (self): return True def  ...
How does the Adapter design pattern stack up?
No harm to base class
No harm to base class Can test with mock-up
No harm to base class Don't need factories Can test with mock-up
No harm to base class Don't need factories Can test with mock-up No collision worries
No harm to base class Don't need factories Can test with mock-up Wrapping is annoying No collision worries
No harm to base class Don't need factories Can test with mock-up Wrapping is annoying Adapter:  B No collision worries
Q:  Why call wrapping “ annoying”?
The example makes it look so easy!
Message object Adapted object IMAP library (or whatever) returns a Message “msg” TreeWidget tw = TreeWidget(TreeMessageAda...
A:  The example looks easy because  it only does adaptation  once !
But in a real application, it happens all through your code...
objects objects 3 rd  party Producers Adapters 3 rd  party Consumers Your application C(msg) DB GUI A(famtree) IMAP email ...
This makes you repeat yourself. This  also   locks you in to using that particular adapter, since you use it by name in yo...
How can you avoid repeating yourself, and scattering information about adapters and consumers everywhere?
Message object Adapted object IMAP library (or whatever) returns a Message “msg” TreeWidget tw = TreeWidget(TreeMessageAda...
tw = TreeWidget(TreeMessageAdapter(msg))
The key is seeing that this code conflates  two  issues! tw = TreeWidget(TreeMessageAdapter(msg))
Why does this line work? tw = TreeWidget(TreeMessageAdapter(msg))
It works because a  TreeWidget   needs  what our adapter  provides . tw = TreeWidget(TreeMessageAdapter(msg))
But if  we  call the adapter then the  need   =   want  is   hidden inside of our head! tw = TreeWidget(TreeMessageAdapter...
We need to define  what the  TreeWidget  needs that our adapter provides!
An  interface  is how we specify a set of behaviors
(1988) (1995) An  interface  is how we specify a set of behaviors
 
For the moment, forget Zope-the-web-framework
Instead, look at Zope the Component Framework: zope.interface zope.component
With three simple steps, Zope will put adapters around classes  for you  — and  rid your code of manual adaptation!
1.  Define  an interface 2.  Register  our adapter 3.  Request  adaptation
from zope.interface import Interface class  ITree (Interface): def  name (): “”” Return this tree node's name. ””” def  ch...
from zope.component import provideAdapter provideAdapter( MessageTreeAdapter , adapts= Message , provides= ITree ) Register
class  TreeWidget (...): def __init__(self, arg): tree =  ITree (arg) ...  Request
class  TreeWidget (...): def __init__(self, arg): tree =  ITree (arg) ...  Zope will: 1. Recognize need 2. Find the regist...
class  TreeWidget (...): def __init__(self, arg): tree =  ITree (arg) ...  (Look! Zope is Pythonic!) i = int(32.1) l = lis...
And that's it!
And that's it! Define  an interface Register  our adapter Request  adaptation
No harm to base class Don't need factories Can test with mock-up Adapters now dynamic! Registered adapter:  A No collision...
objects objects 3 rd  party Producers Adapters 3 rd  party Consumers Your application C(msg) DB GUI A(famtree) IMAP email ...
What adapters provide What consumers need C(msg) DB GUI A(famtree) IMAP email msg Web Widget B(msg) Genealogy A B C C(msg)
DB GUI IMAP email Web Widget Genealogy A B C
The finale Adapting for the Web
dum ... dum ... dum ... DAH DUM!
 
Grok
Web framework built atop Zope 3 component architecture
Grok makes Zope 3 simple to use (and to present!)
Imagine a  Person  class
The  Person  class was written by someone else
The  Person  class is full of business logic, and stores instances in a database
We want to browse  Person  objects on the Web
What might the Web need the object to do?
1. What's at a URL 3. What is its URL 2. HTML document <HTML> <HEAD> <TITLE>Person JOE </TITLE> </HEAD> <BODY> This page p...
1.
What's at this URL?
What's at this URL? # how Zope processes this URL: r = root j = ITraverser(r).traverse('person_app') k = ITraverser(j).tra...
# what we write: class  PersonTraverser (grok. Traverser ): grok.context(PersonApp) def  traverse (self,  name ): if perso...
2.
How does a Person render?
app.py class  PersonIndex (grok. View ): grok.context( Person ) grok.name(' index ') app_templates/personindex.pt < html >...
3.
What is a person's URL?
class  PersonURL (grok. MultiAdapter ): grok.adapts(Person, IHTTPRequest) grok.implements(IAbsoluteURL) def  __init__ (sel...
6 + 3 + 8 = 17 lines
6 + 3 + 8 = 17 lines And the object has not been harmed!
1. What's at a URL 3. What is its URL 2. HTML Document <HTML> <HEAD> <TITLE>Person JOE </TITLE> </HEAD> <BODY> This page p...
Other Zope adapter uses
Other Zope adapter uses Indexing — Index, Query, Search, ... Data schemas — Schema, Vocabulary, DublinCore ... Form genera...
Other Zope adapter uses And... “Vice”, the Plone RSS/Atom feed engine that Paul Bugni presented on yesterday!
How does Vice give the AT content types RSS superpowers?
The same 3 steps! Define  an interface Register  adapters Request  adaptation
ATDocument ATEvent ATLink ATImage ATFile ATNewsItem IFeedItem IFeedItem IFeedItem IFeedItem IFeedItem IFeedItem Adapter Ad...
Adapters can be local! Global adapters Local adapters add, override http://host/person_app/Joe http:// person_app Joe
Coming Attraction
five.grok
five.grok Lennart Regebro Martin Aspeli
Thank you! http://zope.org/ Products/Zope3 http://grok.zope.org/ http://rhodesmill.org/brandon/adapters http://regebro.wor...
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Using Grok to Walk Like a Duck - Brandon Craig Rhodes

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Using Grok to Walk Like a Duck - Brandon Craig Rhodes

  1. 1. “ Using Grok to Walk Like a Duck” The Zope 3 Component Architecture Brandon Craig Rhodes Plone Conference 2008, Washington, DC
  2. 2. How many methods does a Plone ATFolder have?
  3. 3. Contributors CreationDate Creator Creators DELETE Date Description EffectiveDate ExpirationDate Format HEAD Identifer Identifier LOCK Language MKCOL MKCOL_handler MOVE ModificationDate OPTIONS PROPFIND PROPPATCH PUT PUT_factory ZopeFind Publisher Rights SQLConnectionIDs Schema Schemata SearchableText Subject TRACE Title Type UID UNLOCK Vocabulary ZQueryIds ZopeFind ZopeFindAndApply __url __before_publishing_travers __bobo_traverse__ __browser_default__ __call__ __class_init__ __contains__ __delitem__ __getitem__ __init__ __iter__ __len__ __of__ __repr__ __setitem__ _facade _canCopy _catalogRefs _catalogUID _checkId _ct_defaultAddableTypeIds _ct_defaultConstrainTypesMo _ct_vocabularyPossibleTypes _datify _delOb _delObject _delPropValue _delProperty _delReferenceAnnotations _facade _deleteOwnershipAfterAdd _editMetadata _effective_date _expiration_date _filteredItems _findUniqueId _getCatalogTool _getCopy _getOb getPortalTypeName _getReferenceAnnotations _getURL _getWorkflowTool _get_id _has_user_defined_role _importObjectFromFile _isBeingAccessedAsZClassDef _isBeingUsedAsAMethod _isIDAutoGenerated _isSchemaCurrent _migrateGetValue _migrateSetValue _notifyOfCopyTo _postCopy _processForm _propertyMap _referenceApply _register _renameAfterCreation _setId _setOb _setObject _setPortalTypeName _setPropValue _setProperty _setRoles _setUID _subobject_permissions _uncatalogRefs _uncatalogUID _unregister _updateCatalog _updateProperty _updateSchema _verifyObjectPaste _wrapperCheck absolute_url absolute_url_path ac_inherited_permissions access_debug_info acquiredRolesAreUsedBy addCreator addDTMLDocument addDTMLMethod addReference addSubObjects all_meta_types allowDiscussion allowedContentTypes at_post_create_script at_post_edit_script autoOrderItems bobobase_modification_time canSetConstrainTypes canSetDefaultPage canSetLayout cb_dataItems cb_dataValid cb_isCopyable cb_isMoveable cb_userHasCopyOrMovePermiss changeOwnership checkCreationFlag checkIdAvailable class_manage_path cleanupLayers cmf_edit contentEffective contentExpired contentIds contentItems contentValues copyLayoutFromParent created dav__init dav__simpleifhandler dav__validate decodeFolderFilter defaultIsDiscussable defaultLanguage defaultRights defaultView deleteReference deleteReferences edit editIsDiscussable editMetadata effective encodeFolderFilter exclude_from_nav expires EditLink filtered_manage_options filtered_meta_types folderlistingFolderContents generateNewId get getActionInfo getAttribute getAttributeNode getAttributes getAvailableLayouts getBRefs getBRelationships getBackReferenceImpl getBRefs getCMFObjectsSubsetIds getCatalogs getCharset getChildNodes getConstrainTypesMode getContentType getDefault getDefaultAddableTypes getDefaultLayout getDefaultPage getDefaultSorting getEffectiveDate getElementsByTagName getExcludeFromNav getExpirationDate getField getFilename getFirstChild getFolderWhenPortalFactory getIcon getId getImmediatelyAddableTypes getLastChild getLayout getLocallyAllowedTypes getLocation getMetadataHeaders getNextPreviousEnabled getNextPreviousParentValue getNextSibling getNodeName getNodeType getNodeValue getObjectPosition getOwner getOwnerDocument getOwnerTuple getParentNode getPhysicalPath on.getPhysicalRoot getPortalTypeName getPreviousSibling getPrimaryField getProperty getPropertyType getRawConstrainTypesMode getRawContributors getRawCreation_date getRawCreators getRawDescription getRawEffectiveDate getRawExcludeFromNav getRawExpirationDate getRawId getRawImmediatelyAddableTyp getRawLanguage getRawLocallyAllowedTypes getRawLocation getRawModification_date getRawNextPreviousEnabled getRawRelatedItems getRawRights getRawSubject getRawTitle getReferenceImpl getReferenceMap getReferencePng getRefs getRefs getRelatedItems getRelationships getSiteManager getSortAuto getSortFolderishFirst getSortReverse getSubObject getTagName getTypeInfo getWrappedField getWrappedOwner getContentType get_local_roles get_local_roles_for_userid get_portal_metadata get_request_var_or_attr get_size get_valid_userids hasChildNodes hasObject hasProperty hasRelationshipTo has_local_roles http__etag http__parseMatchList http__processMatchHeaders http__refreshEtag getIcon indexObject initializeArchetype initializeLayers invokeFactory isBinary isDiscussable isTemporary isTransformable items keys languages listContributors listCreators listDAVObjects listFolderContents list_imports locked_in_version manage_CopyContainerAllItem manage_CopyContainerFirstIt manage_DAVget manage_FTPget manage_FTPlist manage_FTPstat manage_access _facade addDTMLDocument addDTMLMethod addDTMLMethod manage_addFile manage_addFolder manage_addImage _facade manage_addOrderedFolder manage_addProperty manage_addSiteRoot manage_addUserFolder manage_addZGadflyConnection manage_addZGadflyConnection manage_afterAdd manage_afterClone manage_afterMKCOL manage_afterPUT manage_beforeDelete _facade _facade manage_changeProperties manage_changePropertyTypes manage_clone manage_copyObjects manage_cutObjects manage_defined_roles _facade manage_delObjects manage_delProperties manage_editMetadata manage_editProperties manage_editRoles manage_editedDialog manage_exportObject manage_fixupOwnershipAfterA manage_getPermissionMapping manage_hasId manage_importObject manage_pasteObjects _facade manage_renameObject manage_renameObjects _facade _facade _facade _facade manage_undo_transactions manage_workflowsTab manage_workspace manage_zmi_logout markCreationFlag modified modified_in_version moveObject moveObjectToPosition moveObjectsByDelta moveObjectsDown moveObjectsToBottom moveObjectsToTop moveObjectsUp notifyModified notifyWorkflowCreated objectIds objectIds_d objectItems objectItems_d objectMap objectMap_d objectValues objectValues_d opaqueIds opaqueItems opaqueValues orderObjects owner_info permission_settings permissionsOfRole possible_permissions post_validate pre_validate processForm propdict propertyDescription propertyIds propertyItems propertyLabel propertyMap propertyValues raise_standardErrorMessage rawIsDiscussable reference_url reindexObject reindexObjectSecurity restrictedTraverse rolesOfPermission setConstrainTypesMode setContentType setContributors setCreationDate setCreators setDefaultPage setDefaultSorting setDefaults setDescription setEffectiveDate setExcludeFromNav setExpirationDate setFilename setFormat setId setImmediatelyAddableTypes setLanguage setLayout setLocallyAllowedTypes setLocation setModificationDate setNextPreviousEnabled setRelatedItems setRights setSiteManager setSortAuto setSortFolderishFirst setSortReverse setSubject setTitle superValues tabs_path_default tabs_path_info this title_and_id title_or_id tpURL tpValues undoable_transactions unindexObject unmarkCreationFlag unrestrictedTraverse update userCanTakeOwnership userdefined_roles users_with_local_role cb_dataValid valid_roles valid_property_id valid_roles validate validate_field validate_preferredTypes validate_roles values virtual_url_path widget wl_clearLocks wl_delLock wl_getLock wl_hasLock wl_isLocked wl_lockItems wl_lockTokens wl_lockValues wl_lockmapping wl_setLock
  4. 4. Contributors CreationDate Creator Creators DELETE Date Description EffectiveDate ExpirationDate Format HEAD Identifer Identifier LOCK Language MKCOL MKCOL_handler MOVE ModificationDate OPTIONS PROPFIND PROPPATCH PUT PUT_factory ZopeFind Publisher Rights SQLConnectionIDs Schema Schemata SearchableText Subject TRACE Title Type UID UNLOCK Vocabulary ZQueryIds ZopeFind ZopeFindAndApply __url __before_publishing_travers __bobo_traverse__ __browser_default__ __call__ __class_init__ __contains__ __delitem__ __getitem__ __init__ __iter__ __len__ __of__ __repr__ __setitem__ _facade _canCopy _catalogRefs _catalogUID _checkId _ct_defaultAddableTypeIds _ct_defaultConstrainTypesMo _ct_vocabularyPossibleTypes _datify _delOb _delObject _delPropValue _delProperty _delReferenceAnnotations _facade _deleteOwnershipAfterAdd _editMetadata _effective_date _expiration_date _filteredItems _findUniqueId _getCatalogTool _getCopy _getOb getPortalTypeName _getReferenceAnnotations _getURL _getWorkflowTool _get_id _has_user_defined_role _importObjectFromFile _isBeingAccessedAsZClassDef _isBeingUsedAsAMethod _isIDAutoGenerated _isSchemaCurrent _migrateGetValue _migrateSetValue _notifyOfCopyTo _postCopy _processForm _propertyMap _referenceApply _register _renameAfterCreation _setId _setOb _setObject _setPortalTypeName _setPropValue _setProperty _setRoles _setUID _subobject_permissions _uncatalogRefs _uncatalogUID _unregister _updateCatalog _updateProperty _updateSchema _verifyObjectPaste _wrapperCheck absolute_url absolute_url_path ac_inherited_permissions access_debug_info acquiredRolesAreUsedBy addCreator addDTMLDocument addDTMLMethod addReference addSubObjects all_meta_types allowDiscussion allowedContentTypes at_post_create_script at_post_edit_script autoOrderItems bobobase_modification_time canSetConstrainTypes canSetDefaultPage canSetLayout cb_dataItems cb_dataValid cb_isCopyable cb_isMoveable cb_userHasCopyOrMovePermiss changeOwnership checkCreationFlag checkIdAvailable class_manage_path cleanupLayers cmf_edit contentEffective contentExpired contentIds contentItems contentValues copyLayoutFromParent created dav__init dav__simpleifhandler dav__validate decodeFolderFilter defaultIsDiscussable defaultLanguage defaultRights defaultView deleteReference deleteReferences edit editIsDiscussable editMetadata effective encodeFolderFilter exclude_from_nav expires EditLink filtered_manage_options filtered_meta_types folderlistingFolderContents generateNewId get getActionInfo getAttribute getAttributeNode getAttributes getAvailableLayouts getBRefs getBRelationships getBackReferenceImpl getBRefs getCMFObjectsSubsetIds getCatalogs getCharset getChildNodes getConstrainTypesMode getContentType getDefault getDefaultAddableTypes getDefaultLayout getDefaultPage getDefaultSorting getEffectiveDate getElementsByTagName getExcludeFromNav getExpirationDate getField getFilename getFirstChild getFolderWhenPortalFactory getIcon getId getImmediatelyAddableTypes getLastChild getLayout getLocallyAllowedTypes getLocation getMetadataHeaders getNextPreviousEnabled getNextPreviousParentValue getNextSibling getNodeName getNodeType getNodeValue getObjectPosition getOwner getOwnerDocument getOwnerTuple getParentNode getPhysicalPath on.getPhysicalRoot getPortalTypeName getPreviousSibling getPrimaryField getProperty getPropertyType getRawConstrainTypesMode getRawContributors getRawCreation_date getRawCreators getRawDescription getRawEffectiveDate getRawExcludeFromNav getRawExpirationDate getRawId getRawImmediatelyAddableTyp getRawLanguage getRawLocallyAllowedTypes getRawLocation getRawModification_date getRawNextPreviousEnabled getRawRelatedItems getRawRights getRawSubject getRawTitle getReferenceImpl getReferenceMap getReferencePng getRefs getRefs getRelatedItems getRelationships getSiteManager getSortAuto getSortFolderishFirst getSortReverse getSubObject getTagName getTypeInfo getWrappedField getWrappedOwner getContentType get_local_roles get_local_roles_for_userid get_portal_metadata get_request_var_or_attr get_size get_valid_userids hasChildNodes hasObject hasProperty hasRelationshipTo has_local_roles http__etag http__parseMatchList http__processMatchHeaders http__refreshEtag getIcon indexObject initializeArchetype initializeLayers invokeFactory isBinary isDiscussable isTemporary isTransformable items keys languages listContributors listCreators listDAVObjects listFolderContents list_imports locked_in_version manage_CopyContainerAllItem manage_CopyContainerFirstIt manage_DAVget manage_FTPget manage_FTPlist manage_FTPstat manage_access _facade addDTMLDocument addDTMLMethod addDTMLMethod manage_addFile manage_addFolder manage_addImage _facade manage_addOrderedFolder manage_addProperty manage_addSiteRoot manage_addUserFolder manage_addZGadflyConnection manage_addZGadflyConnection manage_afterAdd manage_afterClone manage_afterMKCOL manage_afterPUT manage_beforeDelete _facade _facade manage_changeProperties manage_changePropertyTypes manage_clone manage_copyObjects manage_cutObjects manage_defined_roles _facade manage_delObjects manage_delProperties manage_editMetadata manage_editProperties manage_editRoles manage_editedDialog manage_exportObject manage_fixupOwnershipAfterA manage_getPermissionMapping manage_hasId manage_importObject manage_pasteObjects _facade manage_renameObject manage_renameObjects _facade _facade _facade _facade manage_undo_transactions manage_workflowsTab manage_workspace manage_zmi_logout markCreationFlag modified modified_in_version moveObject moveObjectToPosition moveObjectsByDelta moveObjectsDown moveObjectsToBottom moveObjectsToTop moveObjectsUp notifyModified notifyWorkflowCreated objectIds objectIds_d objectItems objectItems_d objectMap objectMap_d objectValues objectValues_d opaqueIds opaqueItems opaqueValues orderObjects owner_info permission_settings permissionsOfRole possible_permissions post_validate pre_validate processForm propdict propertyDescription propertyIds propertyItems propertyLabel propertyMap propertyValues raise_standardErrorMessage rawIsDiscussable reference_url reindexObject reindexObjectSecurity restrictedTraverse rolesOfPermission setConstrainTypesMode setContentType setContributors setCreationDate setCreators setDefaultPage setDefaultSorting setDefaults setDescription setEffectiveDate setExcludeFromNav setExpirationDate setFilename setFormat setId setImmediatelyAddableTypes setLanguage setLayout setLocallyAllowedTypes setLocation setModificationDate setNextPreviousEnabled setRelatedItems setRights setSiteManager setSortAuto setSortFolderishFirst setSortReverse setSubject setTitle superValues tabs_path_default tabs_path_info this title_and_id title_or_id tpURL tpValues undoable_transactions unindexObject unmarkCreationFlag unrestrictedTraverse update userCanTakeOwnership userdefined_roles users_with_local_role cb_dataValid valid_roles valid_property_id valid_roles validate validate_field validate_preferredTypes validate_roles values virtual_url_path widget wl_clearLocks wl_delLock wl_getLock wl_hasLock wl_isLocked wl_lockItems wl_lockTokens wl_lockValues wl_lockmapping wl_setLock 471
  5. 5. Both Zope 2 and Plone solve problems by piling more and more methods on an object
  6. 6. Zope 3 does something different Zope 3 uses Adapters
  7. 7. What are adapters? Let's talk programming.
  8. 8. Many programming languages use static typing
  9. 9. float half(int n) { return n / 2.0; }
  10. 10. float half( int n) { return n / 2.0; }
  11. 11. Python typing is dynamic
  12. 12. def half(n): return n / 2.0
  13. 13. You don't worry about whether an object is of the right type
  14. 14. You simply try using it
  15. 15. “ Duck Typing” (Alex Martelli)
  16. 16. “ Duck Typing” Walks like a duck? Quacks like a duck? It's a duck!
  17. 17. def half(n): return n / 2.0
  18. 18. def half(n): return n / 2.0 (Is n willing to be divided by two? Then it's number-ish enough for us!)
  19. 19. Now, imagine...
  20. 20. Imagine a wonderful duck-processing library to which you want to pass an object
  21. 21. But... The object you want to pass isn't a duck?
  22. 22. What if it doesn't already quack?
  23. 23. What if it bears not the least resemblance to a duck!?
  24. 24. Example!
  25. 25. You have a “Message” object from the Python “email” module
  26. 26. >>> from email import message_from_file >>> e = message_from_file(open('msg.txt')) >>> print e <email.message.Message instance at ...> >>> e.is_multipart() True >>> for part in e.get_payload(): ... print part.get_content_type() text/plain text/html
  27. 27. multipart/mixed text/plain multipart/alternative text/plain text/html image/jpeg Messages can be recursive
  28. 28. Imagine that we are writing a Plone email browsing system
  29. 29. And we want to show the parts in a TreeWidget
  30. 30. multipart/mixed
  31. 31. multipart/mixed text/plain multipart/alternative image/jpeg
  32. 32. multipart/mixed text/plain multipart/alternative text/plain text/html image/jpeg
  33. 33. The Tree widget operates on any object with: method name() - returns name under which this tree node should be displayed method children() - returns list of child nodes in the tree method __len__() - returns number of child nodes beneath this one
  34. 34. How can we add these behaviors to our Message?
  35. 35. (How can we make an object which is not a duck behave like a duck?)
  36. 36. 1. Subclassing
  37. 37. Create a “TreeMessage” class that inherits from the “Message” class...
  38. 38. class TreeMessage ( Message ): def name (self): return self.get_content_type() def children (self): if not self.is_multipart(): return [] return [ TreeMessage (part) for part in self.get_payload() ] def __len__ (self): return len(self.children())
  39. 39. What will the test suite look like?
  40. 40. Remember: “ Untested code is broken code” — Philipp von Weitershausen, Martin Aspeli
  41. 41. Your test suite must instantiate a “TreeMessage” and verify its tree-like behavior...
  42. 42. txt = “”” From: persephone@gmail.com To: brandon@rhodesmill.org Subject: what an article! Did you read Arts & Letters Daily today? “”” m = message_from_string(txt, TreeMessage ) assert m. name () == 'text/plain' assert m. children () == [] assert m. __len__ () == 0
  43. 43. We were lucky!
  44. 44. Our test can cheaply instantiate Messages.
  45. 45. txt = “”” From: persephone@gmail.com To: brandon@rhodesmill.org Subject: what an article! Did you read Arts & Letters Daily today? “”” m = message_from_string(txt, TreeMessage ) assert m. name () == 'text/plain' assert m. children () == [] assert m. __len__ () == 0
  46. 46. What if we were subclassing an LDAP connector?! We'd need an LDAP server just to run unit tests!
  47. 47. We were lucky (#2)!
  48. 48. The “message_from_string()” method let us specify an alternate factory!
  49. 49. txt = “”” From: persephone@gmail.com To: brandon@rhodesmill.org Subject: what an article! Did you read Arts & Letters Daily today? “”” m = message_from_string(txt, TreeMessage ) assert m. name () == 'text/plain' assert m. children () == [] assert m. __len__ () == 0
  50. 50. Final note: we have just broken the “Message” class's behavior!
  51. 51. Python library manual 7.10.1 defines “Message”: __len__(): Return the total number of headers, including duplicates.
  52. 52. >>> t = “”” From: persephone@gmail.com To: brandon@rhodesmill.org Subject: what an article! Did you read Arts & Letters Daily today? “”” >>> m = message_from_file(t, Message) >>> print len(m) 3 >>> m = message_from_file(t, TreeMessage) >>> print len(m) 0
  53. 53. So how does subclassing score?
  54. 54. No harm to base class
  55. 55. No harm to base class Cannot test in isolation
  56. 56. No harm to base class Need control of factory Cannot test in isolation
  57. 57. No harm to base class Breaks if names collide Need control of factory Cannot test in isolation
  58. 58. No harm to base class Breaks if names collide Need control of factory Cannot test in isolation Subclassing: D
  59. 59. 2. Using a mixin
  60. 60. Create a “TreeMessage” class that inherits from both “Message” and a “Mixin”...
  61. 61. class Mixin (object): def name (self): return self.get_content_type() def children (self): if not self.is_multipart(): return [] return [ self.__class__(part) for part in self.get_payload() ] def __len__ (self): return len(self.children()) class TreeMessage ( Message , Mixin ): pass
  62. 62. Your test suite can then inherit from a fake, mocked-up “message”...
  63. 63. class FakeMessage ( Mixin ): def get_content_type (self): return 'text/plain' def is_multipart (self): return False def get_payload (self): return '' m = FakeMessage () assert m. name () == 'text/plain' assert m. children () == [] assert m. __len__ () == 0
  64. 64. How does a mixin rate?
  65. 65. No harm to base class
  66. 66. No harm to base class Can test mixin by itself
  67. 67. No harm to base class Need control of factory Can test mixin by itself
  68. 68. No harm to base class Breaks if names collide Need control of factory Can test mixin by itself
  69. 69. No harm to base class Breaks if names collide Need control of factory Can test mixin by itself Mixin: C
  70. 70. 3. Monkey patching
  71. 71. To “monkey patch” a class, you add or change its methods dynamically...
  72. 72. def name (self): return self.get_content_type() def children (self): if not self.is_multipart(): return [] return [ Message (part) for part in self.get_payload() ] def __len__ (self): return len(self.children()) Message . name = name Message . children = children Message . __len__ = __len__
  73. 73. Is this desirable?
  74. 74. Don't care about factory
  75. 75. Changes class itself Don't care about factory
  76. 76. Changes class itself Broken by collisions Don't care about factory
  77. 77. Changes class itself Broken by collisions Don't care about factory Patches fight each other
  78. 78. Changes class itself Broken by collisions Don't care about factory Ruby people do this Patches fight each other
  79. 79. Changes class itself Broken by collisions Don't care about factory Ruby people do this Monkey patching: F Patches fight each other
  80. 80. 4. Adapter
  81. 81. Touted in the Gang of Four book (1994)
  82. 82. Idea: provide “Tree” functions through an entirely separate object Message MessageTreeAdapter get_content_type () name () is_multipart () call children () get_payload () __len__ ()
  83. 83. class MessageTreeAdapter (object): def __init__ (self, message): self. m = message def name (self): return self. m .get_content_type() def children (self): if not self. m .is_multipart(): return [] return [ MessageTreeAdapter (part) for part in self. m .get_payload() ] def __len__ (self): return len(self.children())
  84. 84. How does wrapping look in your code?
  85. 85. Message object Adapted object IMAP library (or whatever) returns a Message “msg” TreeWidget tw = TreeWidget(MessageTreeAdapter(msg))
  86. 86. Test suite can try adapting a mock-up object
  87. 87. class FakeMessage (object): def get_content_type (self): return 'text/plain' def is_multipart (self): return True def get_payload (self): return [] m = MessageTreeAdapter ( FakeMessage ()) assert m. name () == 'text/plain' assert m. children () == [] assert m. __len__ () == 0
  88. 88. How does the Adapter design pattern stack up?
  89. 89. No harm to base class
  90. 90. No harm to base class Can test with mock-up
  91. 91. No harm to base class Don't need factories Can test with mock-up
  92. 92. No harm to base class Don't need factories Can test with mock-up No collision worries
  93. 93. No harm to base class Don't need factories Can test with mock-up Wrapping is annoying No collision worries
  94. 94. No harm to base class Don't need factories Can test with mock-up Wrapping is annoying Adapter: B No collision worries
  95. 95. Q: Why call wrapping “ annoying”?
  96. 96. The example makes it look so easy!
  97. 97. Message object Adapted object IMAP library (or whatever) returns a Message “msg” TreeWidget tw = TreeWidget(TreeMessageAdapter(msg))
  98. 98. A: The example looks easy because it only does adaptation once !
  99. 99. But in a real application, it happens all through your code...
  100. 100. objects objects 3 rd party Producers Adapters 3 rd party Consumers Your application C(msg) DB GUI A(famtree) IMAP email msg Web Widget B(msg) Genealogy A B C C(msg)
  101. 101. This makes you repeat yourself. This also locks you in to using that particular adapter, since you use it by name in your code.
  102. 102. How can you avoid repeating yourself, and scattering information about adapters and consumers everywhere?
  103. 103. Message object Adapted object IMAP library (or whatever) returns a Message “msg” TreeWidget tw = TreeWidget(TreeMessageAdapter(msg))
  104. 104. tw = TreeWidget(TreeMessageAdapter(msg))
  105. 105. The key is seeing that this code conflates two issues! tw = TreeWidget(TreeMessageAdapter(msg))
  106. 106. Why does this line work? tw = TreeWidget(TreeMessageAdapter(msg))
  107. 107. It works because a TreeWidget needs what our adapter provides . tw = TreeWidget(TreeMessageAdapter(msg))
  108. 108. But if we call the adapter then the need = want is hidden inside of our head! tw = TreeWidget(TreeMessageAdapter(msg))
  109. 109. We need to define what the TreeWidget needs that our adapter provides!
  110. 110. An interface is how we specify a set of behaviors
  111. 111. (1988) (1995) An interface is how we specify a set of behaviors
  112. 113. For the moment, forget Zope-the-web-framework
  113. 114. Instead, look at Zope the Component Framework: zope.interface zope.component
  114. 115. With three simple steps, Zope will put adapters around classes for you — and rid your code of manual adaptation!
  115. 116. 1. Define an interface 2. Register our adapter 3. Request adaptation
  116. 117. from zope.interface import Interface class ITree (Interface): def name (): “”” Return this tree node's name. ””” def children (): “”” Return this node's children. ””” def __len__ (): “”” Return how many children. ””” Define
  117. 118. from zope.component import provideAdapter provideAdapter( MessageTreeAdapter , adapts= Message , provides= ITree ) Register
  118. 119. class TreeWidget (...): def __init__(self, arg): tree = ITree (arg) ... Request
  119. 120. class TreeWidget (...): def __init__(self, arg): tree = ITree (arg) ... Zope will: 1. Recognize need 2. Find the registered adapter 3. Wrap and return the argument Request
  120. 121. class TreeWidget (...): def __init__(self, arg): tree = ITree (arg) ... (Look! Zope is Pythonic!) i = int(32.1) l = list('abc') f = float(1024) Request
  121. 122. And that's it!
  122. 123. And that's it! Define an interface Register our adapter Request adaptation
  123. 124. No harm to base class Don't need factories Can test with mock-up Adapters now dynamic! Registered adapter: A No collision worries
  124. 125. objects objects 3 rd party Producers Adapters 3 rd party Consumers Your application C(msg) DB GUI A(famtree) IMAP email msg Web Widget B(msg) Genealogy A B C C(msg)
  125. 126. What adapters provide What consumers need C(msg) DB GUI A(famtree) IMAP email msg Web Widget B(msg) Genealogy A B C C(msg)
  126. 127. DB GUI IMAP email Web Widget Genealogy A B C
  127. 128. The finale Adapting for the Web
  128. 129. dum ... dum ... dum ... DAH DUM!
  129. 131. Grok
  130. 132. Web framework built atop Zope 3 component architecture
  131. 133. Grok makes Zope 3 simple to use (and to present!)
  132. 134. Imagine a Person class
  133. 135. The Person class was written by someone else
  134. 136. The Person class is full of business logic, and stores instances in a database
  135. 137. We want to browse Person objects on the Web
  136. 138. What might the Web need the object to do?
  137. 139. 1. What's at a URL 3. What is its URL 2. HTML document <HTML> <HEAD> <TITLE>Person JOE </TITLE> </HEAD> <BODY> This page presents the basic data we have regarding Joe. ... Person http://host/person_app/Joe http://host/person_app/Joe
  138. 140. 1.
  139. 141. What's at this URL?
  140. 142. What's at this URL? # how Zope processes this URL: r = root j = ITraverser(r).traverse('person_app') k = ITraverser(j).traverse('Joe') return k http://host/person_app/Joe
  141. 143. # what we write: class PersonTraverser (grok. Traverser ): grok.context(PersonApp) def traverse (self, name ): if person_exists( name ): return get_person( name ) return None What's at this URL? http://host/person_app/Joe
  142. 144. 2.
  143. 145. How does a Person render?
  144. 146. app.py class PersonIndex (grok. View ): grok.context( Person ) grok.name(' index ') app_templates/personindex.pt < html >< head >< title >All about < tal tal:replace =”context/name”/> </ title ></ head >... How does a Person render?
  145. 147. 3.
  146. 148. What is a person's URL?
  147. 149. class PersonURL (grok. MultiAdapter ): grok.adapts(Person, IHTTPRequest) grok.implements(IAbsoluteURL) def __init__ (self, person, req): self.person, self.req = person, req def __call__ (self): base = grok.url(grok.getSite()) return base + ' / ' + self.person.name What is a person's URL?
  148. 150. 6 + 3 + 8 = 17 lines
  149. 151. 6 + 3 + 8 = 17 lines And the object has not been harmed!
  150. 152. 1. What's at a URL 3. What is its URL 2. HTML Document <HTML> <HEAD> <TITLE>Person JOE </TITLE> </HEAD> <BODY> This page presents the basic data we have regarding Joe. ... Person PersonTraverser PersonURL PersonIndex http://host/person_app/Joe http://host/person_app/Joe
  151. 153. Other Zope adapter uses
  152. 154. Other Zope adapter uses Indexing — Index, Query, Search, ... Data schemas — Schema, Vocabulary, DublinCore ... Form generation — AddForm, EditForm, ... Security — SecurityPolicy, Proxy, Checker, ... Authentication — Login, Logout, Allow, Require, ... Copy and paste — ObjectMover, ObjectCopier, ... I18n — TranslationDomain, Translator, ... Appearance — Skins, macros, viewlets, ... Much, much more!
  153. 155. Other Zope adapter uses And... “Vice”, the Plone RSS/Atom feed engine that Paul Bugni presented on yesterday!
  154. 156. How does Vice give the AT content types RSS superpowers?
  155. 157. The same 3 steps! Define an interface Register adapters Request adaptation
  156. 158. ATDocument ATEvent ATLink ATImage ATFile ATNewsItem IFeedItem IFeedItem IFeedItem IFeedItem IFeedItem IFeedItem Adapter Adapter Adapter Adapter Adapter Adapter
  157. 159. Adapters can be local! Global adapters Local adapters add, override http://host/person_app/Joe http:// person_app Joe
  158. 160. Coming Attraction
  159. 161. five.grok
  160. 162. five.grok Lennart Regebro Martin Aspeli
  161. 163. Thank you! http://zope.org/ Products/Zope3 http://grok.zope.org/ http://rhodesmill.org/brandon/adapters http://regebro.wordpress.com/ [email_address] mailing list [email_address] mailing list Web Component Development with Zope 3 by PvW

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