In Python 2.7, taxonomy based search doesn't work

from pattern.search import search, taxonomy, Classifier
from pattern.en import parsetree

for flower in ("rose", "lily", "daisy", "daffodil", "begonia"):
      taxonomy.append(flower, type="flower")

tree = parsetree("A field of white daffodils.", lemmata=True) 
result = search("FLOWER", t)                              # TypeError: can't compile 'str' object

The search function fails in 2.7, whereas it works in 3.6.4

Start by reproducing the example using pattern.search.taxonomy and search with Python 2.7, then compare the same flow under Python 3.6.4. Trace the taxonomy-based search call that raises TypeError: can't compile 'str' object. Done means the supplied taxonomy search works on Python 2.7 without that error and continues to work under Python 3.6.4.