您应该尝试这样的事情：
import re
def check_string():
#no need to pass arguments to function if you're not using them
w = raw_input("Input the English word: ")
#open the file using `with` context manager, it'll automatically close the file for you
with open("example.txt") as f:
found = False
for line in f: #iterate over the file one line at a time(memory efficient)
if re.search("\b{0}\b".format(w),line): #if string found is in current line then print it
print line
found = True
if not found:
print('The translation cannot be found!')
check_string() #Now call the function
如果您要搜索确切的单词而不只是子字符串，那么我建议regex在这里使用。
例：
>>> import re
>>> strs = "foo bar spamm"
>>> "spam" in strs
True
>>> bool(re.search("\b{0}\b".format("spam"),strs))
False
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