Error with layer.pendingAllAttributesList

Question

While coding to obtain individual layers' attributes (field) list, I am stymied by the code.

I can identify a specific layer:
MyLayer = QgsMapLayerRegistry.instance().mapLayersByName("TestPoint")
which returns on "print MyLayer":
qgis._core.QgsVectorLayer object at 0x000000000FCC6730
from which I infer I am correctly using MyLayer as a Layer object/pointer (or whatnot...)

However, when I run this:
fields = Mylayer.pendingAllAttributesList()
I force this error:
AttributeError: 'list' object has no attribute 'pendingAllAttributesList'

Following this statement, eventually I would run a "For field in fields...:" indent block, to iterate through the fields, but I can't even get past my error.

I get same/similar errors for other attribute functions within the API, using versions provided in code samples, and best I can tell I am duplicating relevant python code within the samples found. Somehow, I am missing something important about the way the Attributes work, or the coding, or the list or object.

I am using the recently downloaded QGIS 2.6.0 package for windows.

Answer 1

mapLayersByName returns a list-of-QgsMapLayers so you need to use [0] at the end to just get the single one.

The defintion for that function is:

QList<QgsMapLayer*> QgsMapLayerRegistry::mapLayersByName(QString layerName)

Which you can see returns a QList of QgsMapLayer, which is just a list of QgsMapLayers in Pythion.

Use QgsMapLayerRegistry.instance().mapLayersByName("layer")[0] to get a single layer.

Use something like this to hide the logic:

def layers_by_name(name, single=False):
    layers = QgsMapLayerRegistry.instance().mapLayersByName("layer")
    if single:
       return layers[0]
    else:
       return layers

layer = layers_by_name("mylayer", single=True)

Answer 2

This, for future readers. I noted this clue that would be helpful

layerSS = QgsMapLayerRegistry.instance().mapLayersByName("TestPoint") print layerSS
returns:
[< qgis._core.QgsVectorLayer object at 0x000000000FCC6730 >]

while:
layerSS = QgsMapLayerRegistry.instance().mapLayersByName("TestPoint")[0] print layerSS
returns: < qgis._core.QgsVectorLayer object at 0x000000000FCC6730>

Note the square brackets ("[ ... ]", in the first case, indicating that the result was a List with one pointer pointer as an element (a pointer with the "< ... >"), and that my error spoke of lists.

Note the absence of the brackets, in the second case, indicating that the result was a pointer

With that portion of my error identified, my next question should/would have been, how do I get the first/only element of a list. The answer was @Nathans first clue: using the [0].