如果字符串在文本文件中，如何检查 Python 并打印该行？
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How to check in Python if string is in a text file and print the line?
提问by bn60
What I am trying to do is to check whether this string is found in the text file. If it does, I want it to printout that line, else printout a message.
我想要做的是检查是否在文本文件中找到了这个字符串。如果是这样，我希望它打印出该行，否则打印出一条消息。
I have implemented this code so far:
到目前为止，我已经实现了这段代码：
def check_string(string):
w = raw_input("Input the English word: ")
if w in open('example.txt').read():
for w.readlines():
print line
else:
print('The translation cannot be found!')
I've tried implementing that but I got a syntax error.
我试过实现它，但出现语法错误。
It says:
它说：
invalid syntax at the line -- for w.readlines():
该行的语法无效——对于 w.readlines()：
Any idea on how to go with this line of code?
关于如何使用这行代码的任何想法？
采纳答案by Ashwini Chaudhary
You should try something like this:
你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
If you are searching for exact words instead of just sub-string then I would suggest using regexhere.
如果您正在搜索确切的单词而不仅仅是子字符串，那么我建议regex在此处使用。
Example:
例子：
>>> import re
>>> strs = "foo bar spamm"
>>> "spam" in strs
True
>>> bool(re.search("\b{0}\b".format("spam"),strs))
False
回答by kenorb
Here is a bit simpler example by using inoperator:
这是一个使用in运算符的更简单的示例：
w = raw_input("Input the English word: ") # For Python 3: use input() instead
with open('foo.txt') as f:
found = False
for line in f:
if w in line: # Key line: check if `w` is in the line.
print(line)
found = True
if not found:
print('The translation cannot be found!')
If you'd like to know the position of the string, then you can use find()instead of inoperator.
如果您想知道字符串的位置，则可以使用find()代替in运算符。
