You can strip whitespace from the start and end of the lines, and if there are still spaces in the string you have a sentence:
if u' ' not in line.strip():
# line is a *not* a sentence
Open your file with io.open()
instead; to write just the lines that are not sentences you can use a simple generator expression:
import io
with io.open('olam-enml.txt', 'r', encoding='utf8') as infh:
with io.open('olam-enml-words.txt', 'w', encoding='utf8') as outfh:
outfh.writelines(line for line in infh if u' ' not in line.strip())