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"

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):

with open('example.txt') as f:
    if 'blabla' in f.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

with open('example.txt') as f:
    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):

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():
    with open('example.txt') as f:
        datafile = f.readlines()
    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

Then you can test the output of check():

if check():
    print('True')
else:
    print('False')

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

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!

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.

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"

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"

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

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"

If user wants to search for the word in given text file.

 fopen = open('logfile.txt',mode='r+')

  fread = fopen.readlines()

  x = input("Enter the search string: ")

  for line in fread:

      if x in line:

          print(line)

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

if check():
    print "found"
else:
    print "not found"