Python 2.7和QGIS 2.6：减去两个值并将要素ID添加到列表中

Question

我想从qgs要素迭代器对象中减去两个值，并根据条件将要素ID的值附加到列表中。

在qgis的上下文中，我有两个层次： roadsLayer pathsLayer

我到目前为止返回一个空列表：

evenList = []
azimuthRoadsIDX = roadsLayer.fieldNameIndex('azimuth')
azimuthPathsIDX = pathsLayer.fieldNameIndex('azimuth')
roads = roadsLayer.getFeatures()
paths = pathsLayer.getFeatures()
for feat in roads:
    for feature in paths:
        roadsAzimuth = feat.attributes()[azimuthRoadsIDX]
        pathsAzimuth = feature.attributes()[azimuthPathsIDX]
        if (roadsAzimuth - pathsAzimiuth == 90) or (roadsAzimuth - pathsAzimth == -270):
            evenList.append(feature.id())

不知道为什么，但这有效。唯一的问题是它在所有情况下都不起作用（即使在roadsAzimuth - pathsAzimuth == 90时，在某些情况下也没有附加）：

for feat in roadsLayer.getFeatures():
    roadsAzimuth = feat.attributes()[azimuthRoadsIDX]
    for feature in pathsLayer.getFeatures():
        pathsAzimuth = feature.attributes()[azimuthPathsIDX]
        if (roadsAzimuth - pathsAzimiuth == 90) or (roadsAzimuth - pathsAzimth == -270):
            evenList.append(feature.id())