import re
sentence = ['if', 'it', 'will', 'rain', ',', 'if', 'will', 'stay', 'at', ',', 'home']
s = ' '.join(sentence)
p = re.compile("((\\bif\\b)[a-zA-z0-9\\'\\s]+)\\s*(,*)\\s*(then|,)")
arr = re.findall(p, s)
pos = 0
for i, x in enumerate(arr):
start = sentence.index(x[1], pos)
end = sentence.index(x[3], pos)
stri = ' '.join(sentence[start: end])
print(stri)
pos = sentence.index(x[3], pos) + 1
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