BUG: attributes are wrapped in tuples

[bzah]

Description

It seems when attributes are not strings, the value is wrapped with a tuple.

What I Did

cat >test.xml << EOF
<?xml version="1.0" encoding="UTF-8"?> 
<netcdf xmlns="http://www.unidata.ucar.edu/namespaces/netcdf/ncml-2.2">
  <attribute name="toto" type="double" value="42.42" />
  <attribute name="cacao" type="string" value="cacao" />
</netcdf>   
EOF

from xncml import open_ncml

ds = open_ncml("test.xml")
# OK.
assert type(ds.attrs["cacao"]) == str
# KO (the type is actually tuple)
assert type(ds.attrs["toto"]) == float

• I'm willing to investigate/fix this issue.