How to search for a string in text files?

问题:

I want to check if a string is in a text file. If it is, do X. If it\'s not, do Y. However, this code always returns True for some reason. Can anyone see what is wrong?

def check():
    datafile = file(\'example.txt\')
    found = False
    for line in datafile:
        if blabla in line:
            found = True
            break

check()
if True:
    print \"true\"
else:
    print \"false\"

回答1:

The reason why you always got True has already been given, so I\'ll just offer another suggestion:

If your file is not too large, you can read it into a string, and just use that (easier and often faster than reading and checking line per line):

if \'blabla\' in open(\'example.txt\').read():
    print(\"true\")

Another trick: you can alleviate the possible memory problems by using mmap.mmap() to create a \"string-like\" object that uses the underlying file (instead of reading the whole file in memory):

import mmap

f = open(\'example.txt\')
s = mmap.mmap(f.fileno(), 0, access=mmap.ACCESS_READ)
if s.find(\'blabla\') != -1:
    print(\'true\')

NOTE: in python 3, mmaps behave like bytearray objects rather than strings, so the subsequence you look for with find() has to be a bytes object rather than a string as well, eg. s.find(b\'blabla\'):

#!/usr/bin/env python3
import mmap

with open(\'example.txt\', \'rb\', 0) as file, \\
     mmap.mmap(file.fileno(), 0, access=mmap.ACCESS_READ) as s:
    if s.find(b\'blabla\') != -1:
        print(\'true\')

You could also use regular expressions on mmap e.g., case-insensitive search: if re.search(br\'(?i)blabla\', s):

回答2:

As Jeffrey Said, you are not checking the value of check(). In addition, your check() function is not returning anything. Note the difference:

def check():
    datafile = file(\'example.txt\')
    found = False #this isn\'t really necessary 
    for line in datafile:
        if blabla in line:
            #found = True #not necessary 
            return True
    return False #because you finished the search without finding 

anything

print check()

回答3:

Here\'s another way to possibly answer your question using the find function which gives you a literal numerical value of where something truly is

open(\'file\', \'r\').read().find(\'\')

in find write the word you want to find and \'file\' stands for your file name

回答4:

if True:
    print \"true\"

This always happens because True is always True.

You want something like this:

if check():
    print \"true\"
else:
    print \"false\"

Good luck!

回答5:

I made a little function for this purpose. It searches for a word in the input file and then adds it to the output file.

def searcher(outf, inf, string):
    with open(outf, \'a\') as f1:
        if string in open(inf).read():
            f1.write(string)

• outf is the output file
• inf is the input file
• string is of course, the desired string that you wish to find and add to outf.

回答6:

Your check function should return the found boolean and use that to determine what to print.

def check():
        datafile = file(\'example.txt\')
        found = False
        for line in datafile:
            if blabla in line:
                found = True
                break

        return found

found = check()
if found:
    print \"true\"
else:
    print \"false\"

the second block could also be condensed to:

if check():
    print \"true\"
else:
    print \"false\"

回答7:

How to search the text in the file and Returns an file path in which the word is found (Как искать часть текста в файле и возвращять путь к файлу в котором это слово найдено)

import os
import re

class Searcher:
    def __init__(self, path, query):
        self.path   = path

        if self.path[-1] != \'/\':
            self.path += \'/\'

        self.path = self.path.replace(\'/\', \'\\\\\')
        self.query  = query
        self.searched = {}

    def find(self):
        for root, dirs, files in os.walk( self.path ):
            for file in files:
                if re.match(r\'.*?\\.txt$\', file) is not None:
                    if root[-1] != \'\\\\\':
                        root += \'\\\\\'           
                    f = open(root + file, \'rt\')
                    txt = f.read()
                    f.close()

                    count = len( re.findall( self.query, txt ) )
                    if count > 0:
                        self.searched[root + file] = count

    def getResults(self):
        return self.searched

In Main()

# -*- coding: UTF-8 -*-

import sys
from search import Searcher

path = \'c:\\\\temp\\\\\'
search = \'search string\'


if __name__ == \'__main__\':

    if len(sys.argv) == 3:
        # создаем объект поисковика и передаем ему аргументы
        Search = Searcher(sys.argv[1], sys.argv[2])
    else:
        Search = Searcher(path, search)

    # начать поиск
    Search.find()

    # получаем результат
    results = Search.getResults()

    # выводим результат
    print \'Found \', len(results), \' files:\'

    for file, count in results.items():
        print \'File: \', file, \' Found entries:\' , count

回答8:

Two problems:

1. Your function does not return anything; a function that does not explicitly return anything returns None (which is falsy)

2. True is always True - you are not checking the result of your function

.

def check(fname, txt):
    with open(fname) as dataf:
        return any(txt in line for line in dataf)

if check(\'example.txt\', \'blabla\'):
    print \"true\"
else:
    print \"false\"

回答9:

found = False

def check():
    datafile = file(\'example.txt\')
    for line in datafile:
        if blabla in line:
            found = True
            break
    return found

if check():
    print \"true\"
else:
    print \"false\"