How to check in Python if string is in a text file and print the line?

问题

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.

I have implemented this code so far:

 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.

It says:

invalid syntax at the line -- for w.readlines():

Any idea on how to go with this line of code?

回答1:

You should try something like this:

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 regex here.

Example:

>>> import re
>>> strs = "foo bar spamm"
>>> "spam" in strs        
True
>>> bool(re.search("\b{0}\b".format("spam"),strs))
False

回答2:

Here is a bit simpler example by using in operator:

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 in operator.

来源：https://stackoverflow.com/questions/16432203/how-to-check-in-python-if-string-is-in-a-text-file-and-print-the-line

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