incf.dai 0.7

Python API for the INCF Digital Atlasing infrastructure

Discovering and Accessing Hubs

In a nutshell the INCF DAI consistes of a network of so-called hubs providing whatever services the group managing the hub decided to share. To discover available hubs there is a utility function

>>> from incf.dai.utils import list_hub_names
>>> sorted(list_hub_names())
['aba', 'central', 'emap', 'ucsd', 'whs']

This provides a list of currently known hub names. (Note: atm the list is provided by the package since the INCF central hub managing the registry is a fast moving target still.)

Knowing the names of available hubs one can optain proxy objects specific for a particular hub by calling

>>> from incf.dai.utils import get_hub_by_name
>>> whs = get_hub_by_name('whs')
>>> whs # doctest: +ELLIPSIS
<incf.dai.hub.HubProxy object at ...>

If you call for an unknow hub (or make a typo) you will get a KeyError

>>> foo = get_hub_by_name('foo')
Traceback (most recent call last):
KeyError

For introspection the URL to the service controller for this hub is available as

>>> whs.base_url
'http://incf-dev-local.crbs.ucsd.edu/whs/atlas?service=WPS'

There are two methods all hubs are expected to provide:

>>> whs.GetCapabilities  # doctest: +ELLIPSIS
<bound method HubProxy.GetCapabilities of ...>

>>> whs.DescribeProcess # doctest: +ELLIPSIS
<bound method HubProxy.DescribeProcess of ...>

Calling any of those methods returns a custom response object

>>> response = whs.GetCapabilities()
>>> response  # doctest: +ELLIPSIS
<incf.dai.response.Response object at 0x...>

>>> response = whs.DescribeProcess()
>>> response  # doctest: +ELLIPSIS
<incf.dai.response.Response object at 0x...>

Usually, there is no need to call any of the two methods mentioned above as their main information returned is available anyway via

>>> sorted(whs.capabilities)
[u'DescribeSRS', u'GetStructureNamesByPOI', u'ListSRSs', u'ListTransformations', u'TransformPOI']

and all methods listed are available on the hub proxy right away

>>> sorted(whs.__dict__.keys())   # doctest: +NORMALIZE_WHITESPACE
['DescribeSRS', 'GetStructureNamesByPOI', 'ListSRSs',
'ListTransformations', 'TransformPOI', 'base_url',
'capabilities', 'process_descriptions', 'proxy']

like in

>>> response = whs.ListSRSs()
>>> sorted(response.keys())  # doctest: +NORMALIZE_WHITESPACE
[u'service', u'serviceInstance', u'version', u'wps_Process',
u'wps_ProcessOutputs', u'wps_Status', u'xml_lang', u'xmlns_ogc',
u'xmlns_ows', u'xmlns_wps', u'xmlns_xlink', u'xmlns_xsi',
u'xsi_schemaLocation']

>>> response['wps_ProcessOutputs']['wps_Output']['wps_Data']['wps_ComplexData']['ListSRSResponse']['SRSCollection']['SRSList']  # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
{SRS:[{Area:{structureName:u'Whole Brain'},
       Author:{authorCode:u'WHS', ...

For further convenience, the response object also supports attribute-like access to the data as in

>>> response.wps_Status  # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
{creationTime:...

Note how the namespaces are preserved as prefixes of the key and attribute names.

Omitting required arguments raises an ApplicationError

>>> response = whs.DescribeSRS()  # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
Traceback (most recent call last):
...
ApplicationError:
Code: NoApplicableCode
Text: Unexpected exception occured
URL:  http://incf-dev-local.crbs.ucsd.edu/whs/atlas?service=WPS&version=1.0.0&request=Execute&Identifier=DescribeSRS&ResponseForm=xml

whereas calling a method correctly gives and appropriate response (hopefully)

>>> response = whs.GetStructureNamesByPOI(format=None, srsName="Mouse_paxinos_1.0", x='1', y='4.3', z='1.78')  # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
>>> response.keys()
[u'xmlns_xlink', u'wps_Process', u'xml_lang', u'wps_Status', u'wps_ProcessOutputs', u'service', u'xmlns_xsi', u'xmlns_ows', u'xsi_schemaLocation', u'version', u'xmlns_ogc', u'xmlns_wps', u'serviceInstance']
>>> response.wps_ProcessOutputs.wps_Output.wps_Data.wps_ComplexData.StructureTermsResponse.StructureTerms.StructureTerm.Code.data
u'Cx'

The format=None here works around issue http://code.google.com/p/incf-dai/issues/detail?id=14

The Response in detail

The custom response object returned from service calls provides a variety of useful information like the HTTP response headers

>>> sorted(response.headers.keys())  # doctest: +NORMALIZE_WHITESPACE
['connection', 'content-location', 'content-type', 'date', 'status',
'transfer-encoding']

and for convenience there is a short-cut to the content type

>>> response.content_type
'text/xml;charset=UTF-8'

The source of the returned response page is available as

>>> response.content # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
'<?xml version="1.0" encoding="UTF-8"?>\n...

which is probably more readable when printed (for this doc test calling print response is avoided but in an interactive session it should work just fine)

>>> str(response)  # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
'<?xml version="1.0" ?><wps:ExecuteResponse service="WPS"  ...

If the content type is XML there will also be a 'data' attribute holding the parsed response

>>> type(response.data)
<class 'incf.dai.utils.DataNode'>

which acts like a nested dictionary

>>> response.data.keys() # doctest: +ELLIPSIS +NORMALIZE_WHITESPACE
[u'xmlns_xlink', u'wps_Process', u'xml_lang', u'wps_Status',
u'wps_ProcessOutputs', u'service', u'xmlns_xsi', u'xmlns_ows',
u'xsi_schemaLocation', u'version', u'xmlns_ogc', u'xmlns_wps',
u'serviceInstance']

>>> wps_Data = response.data['wps_ProcessOutputs']['wps_Output']['wps_Data']
>>> wps_Data['wps_ComplexData']['StructureTermsResponse']['StructureTerms']  # doctest: +NORMALIZE_WHITESPACE
{StructureTerm:{Code:{codeSpace:u'Mouse_paxinos_1.0',
isDefault:u'true', data:u'Cx'}, Description:u'Term - Cx
derived from WHS hub based on the supplied POI.', Name:''}, hubCode:u'WHS'}

but also supports attribute-like access (as long as the keys don't contain characters that make them unsuited as attribute names - in those cases only subscription access works)

>>> response.data.xmlns_xsi
u'http://www.w3.org/2001/XMLSchema-instance'

Again for convenience, the data attribute can be bypassed as the data content is lifted" to the response object itself

>>> response.data.keys() == response.keys()
True

and

>>> response.xmlns_xsi
u'http://www.w3.org/2001/XMLSchema-instance'

Digging deeper into the response data requires knowledge of the response schema which is available from http://incf.org/WaxML or introspection of the content of the response.data attribute.

Improving Performance

Accessing a hub by calling get_hub_by_name as presented above triggers calling DescribeProcess on hub proxy initialization to infer the hubs capabilities and to dynamically create methods making those capabilities readily available on the hub proxy. Depending on context and intended usage you may want to avoid that overhead and rather prefer a "naked" hub proxy as in

>>> whs_minimal = get_hub_by_name('whs', minimal=True)

This avoids calling DescribeProcess on initialization but in return all you are left with is the generic call method that requires you to pass all arguments needed to construct the proper WPS request

>>> response = whs_minimal(version='1.0.0', request='Execute', identifier='ListSRSs')
>>> sorted(response.keys()) # doctest: +NORMALIZE_WHITESPACE
[u'service', u'serviceInstance', u'version', u'wps_Process',
u'wps_ProcessOutputs', u'wps_Status', u'xml_lang', u'xmlns_ogc',
u'xmlns_ows', u'xmlns_wps', u'xmlns_xlink', u'xmlns_xsi',
u'xsi_schemaLocation']

Once you know what you need to call from your own code you may prefer this approach.

Logging

Per default, all service calls are logged at INFO level to a custom log file (incf.dai.log)in the current working directory including a time stamp, the package name, the log level and the URL called.

Accessing Hubs not registered at INCF

To connect to a hub not registered with INCF Central (e.g., a local hub under development) one can instanciate the proxy explicitly as in (setting offline=True avoids ever calling the url)

>>> from incf.dai.hub import HubProxy
>>> myhub = HubProxy('http://some.url?service=WPS', offline=True)
>>> myhub   # doctest: +ELLIPSIS
<incf.dai.hub.HubProxy object at ...>

At the very least the generic call method to be invoked as in

>>> capabilities = myhub(version=None, request='GetCapabilities')
Requested URL: http://some.url?service=WPS&request=GetCapabilities&ResponseForm=xml
positional arguments: ('GET',)

should always be available. The first argument here is to override the version specification which is not supported for GetCapabilities calls. Second is the name of the request to be invoked at the hub. For convenience GetCapabilities is also provided as a method on the hub proxy itself.

>>> myhub.GetCapabilities()  # doctest: +ELLIPSIS
Requested URL: http://some.url?service=WPS&request=GetCapabilities&ResponseForm=xml
positional arguments: ('GET',)
<incf.dai.response.Response object at ...>

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