You can do this with pandas:
import pandas as pd
from io import StringIO
io = StringIO('''\
id A B C D E
100 1 0 0 0 0
101 0 1 1 0 0
102 1 0 0 0 0
103 0 0 0 1 1
''')
df = pd.read_csv(io, sep='\s+', index_col='id')
val = df.apply(lambda row: ' '.join(df.columns[row==1]), axis=1)
Google for "boolean indexing" to see what's going on :)
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