Obtaining the data of one selected feature in QGIS using Python?

Calling layer.selectedFeatures() will return a list with your selected feature(s). You can then call feature.attributeMap() on each of the selected features to get a dictionary of each feature's attributes.

layer = qgis.utils.iface.activeLayer()
selected_features = layer.selectedFeatures()
for i in selected_features:
    attrs = i.attributeMap()
    for (k,attr) in attrs.iteritems():
    print "%d: %s" % (k, attr.toString())

I recently had a similar question answered here: When iterating over a vector layer with pyqgis, how do I check whether a feature is selected?

I just wanted to post some updates to the previous answer in light of changes to the QGIS Python API since version 2.0.

As before, you would get a list of selected features with iface.activeLayer().selectedFeatures(), however in QGIS versions >= 2.0 you now use the function QgsFeature.attributes() instead of QgsFeature.attributeMap(). The two functions are not exactly the same: attributes() now returns a list, whereas the old attributeMap() returned a dictionary. Take a moment to browse the API documentation for QgsFeature.attributes(), QgsAttributes, etc to understand how attributes are stored/accessed.

If you're interested, you can read about some of the rationale behind the API changes on this mailing list thread: [Qgis-developer] new vector api select features. Briefly (in the words of QGIS developer Martin Dobias):

Access to attributes: there is no f.attributeMap() anymore, because attributes are now stored in a vector (Python: list) instead of a map (Python: dict). QgsFeature class emulates python container object 4 so you can access attributes as if QgsFeature instance was a list or dictionary, with keys being either field indices or field names:

f[0] ... first attribute

f["type"] ... attribute named "type"

It is still possible to get all attributes: f.attributes() returns a list of values.

So as an example of specifically what you asked how to do (get data for a single feature you've selected), suppose you had a layer of containing city features that each have a list of attributes, including a county attribute. To get the county value for a specific city you've selected (say Helena, AR), do the following in the Python console:

city = iface.activeLayer().selectedFeatures()[0]
city["county"]
# OUTPUTS: u'Phillips'

If you want the values of all of the fields in the city's attribute table, then you would just use:

cityData = city.attributes()