Why Does My String Search in Python Text Files Always Return True?

Search for a String within Text Files

In an attempt to determine the presence of a specific string within a text file, a program may encounter unexpected behavior. To rectify this issue, it's crucial to understand the underlying reason behind the incorrect results.

Original Code:

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"

Reason for False Results:

The provided code consistently returns True regardless of the string's presence in the file because the evaluation of 'if True' in the following block is not tied to the logic of the preceding loop.

if True:
    print "true"
else:
    print "false"

Python with Open:

An alternative approach to reading a text file is to utilize the 'with' statement in conjunction with the 'open()' function. This method creates a 'file-like' object that automatically handles file closing.

with open('example.txt') as f:
    if 'blabla' in f.read():
        print("true")

Using Memory Mapping:

Another technique for working with text files is memory mapping. This approach reads the entire file into memory as a string-like object, enabling faster access and the possibility of using regular expressions.

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')

By following these suggestions, you can accurately search for strings within text files and obtain the expected results.

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