Asked  6 Months ago    Answers:  5   Viewed   22 times

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"

 Answers

91

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):

Tuesday, June 1, 2021
 
Dev
answered 6 Months ago
Dev
27

python3 is not Python syntax, it is the Python binary itself, the thing you run to get to the interactive interpreter.

You are confusing the command line with the Python prompt. Open a console (Windows) or terminal (Linux, Mac), the same place you'd use dir or ls to explore your filesystem from the command line.

If you are typing at a >>> or In [number]: prompt you are in the wrong place, that's the Python interpreter itself and it only takes Python syntax. If you started the Python prompt from a command line, exit at this point and go back to the command line. If you started the interpreter from IDLE or in an IDE, then you need to open a terminal or console as a separate program.

Other programs that people often confuse for Python syntax; each of these is actually a program to run in your command prompt:

  • python, python2.7, python3.5, etc.
  • pip or pip3
  • virtualenv
  • ipython
  • easy_install
  • django-admin
  • conda
  • flask
  • scrapy
  • setup.py -- this is a script you need to run with python setup.py [...].
  • Any of the above together with sudo.

with many more variations possible depending on what tools and libraries you have installed and what you are trying to do.

If given arguments, you'll get a SyntaxError exception instead, but the underlying cause is the same:

>>> pip install foobar
  File "<stdin>", line 1
    pip install foobar
              ^
SyntaxError: invalid syntax
Tuesday, June 1, 2021
 
QuantumMechanic
answered 6 Months ago
97
 List <String> list = new ArrayList();  
           list.add("behold"); 
           list.add("bend"); 
           list.add("bet"); 
           list.add("bear"); 
           list.add("beat"); 
           list.add("become"); 
           list.add("begin");

           List <String> listClone = new ArrayList<String>(); 
           for (String string : list) {
               if(string.matches("(?i)(bea).*")){
                   listClone.add(string);
               }
           }
        System.out.println(listClone);
Sunday, August 1, 2021
 
astaykov
answered 4 Months ago
58

use the following to convert to a timestamp in python 2

int((mod_time.mktime(first_run.timetuple())+first_run.microsecond/1000000.0))

Sunday, August 22, 2021
 
waylaidwanderer
answered 4 Months ago
98

If I right understood you are searching for a string value (suppose some runtime value) among all values available in your program during the run. If so, I don't think it's even possible, not that I'm aware of, from Visual Studio. There are always hacking solution for that, like dump process memory, read assembly, but even there you can met problems, if (just an example) the program (at this point I suppose it wasn't written by you) store the values in SecureString.

If this is not your intention, please clarify.

Wednesday, October 20, 2021
 
Igor Tupitsyn
answered 1 Month ago
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