[nested dics] Easy way to find if a key exists?

[Winfried]

For some reason, it finds 'Placemark', but not 'LineString', altough both are nested dictionaries:

print(key_exists2(doc, 'Placemark'))
#True
print(key_exists2(doc, 'LineString'))
#False

input.kml:

<?xml version="1.0" encoding="utf-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2">
  <Document>
    <name>Document.kml</name>
    <open>1</open>
    <Style id="exampleStyleDocument">
      <LabelStyle>
        <color>ff0000cc</color>
      </LabelStyle>
    </Style>
    <Placemark>
      <name>Document Feature 1</name>
      <styleUrl>#exampleStyleDocument</styleUrl>
      <Point>
        <coordinates>-122.371,37.816,0</coordinates>
      </Point>
    </Placemark>
    <Placemark>
      <name>Document Feature 2</name>
      <styleUrl>#exampleStyleDocument</styleUrl>
      <Point>
        <coordinates>-122.370,37.817,0</coordinates>
      </Point>
    </Placemark>
    <Placemark>
      <name>My track</name>
      <LineString>
        <coordinates>-0.376291,43.296237,199.75
        -0.377381,43.29405</coordinates>
      </LineString>
    </Placemark>
  </Document>
</kml>