Create a .Txt File If Doesn't Exist, and If It Does Append a New Line

Create a .txt file if doesn't exist, and if it does append a new line

Use the correct constructor:

else if (File.Exists(path))
{
    using(var sw = new StreamWriter(path, true))
    {
        sw.WriteLine("The next line!");
    }
}

Writing to a new file if it doesn't exist, and appending to a file if it does

It's not clear to me exactly where the high-score that you're interested in is stored, but the code below should be what you need to check if the file exists and append to it if desired. I prefer this method to the "try/except".

import os
player = 'bob'

filename = player+'.txt'

if os.path.exists(filename):
    append_write = 'a' # append if already exists
else:
    append_write = 'w' # make a new file if not

highscore = open(filename,append_write)
highscore.write("Username: " + player + '\n')
highscore.close()

c# - How to create a file if it doesn't exist yet and add new text?

Try this

        string path = @"Your File Path";

        bool done = false;

        while (!done)
        {
            done = true;

            try
            {
                FileStream fileStream = null;
                fileStream = File.Open(path, File.Exists(path) ? FileMode.Append : FileMode.OpenOrCreate);

                using (StreamWriter fs = new StreamWriter(fileStream))
                {
                    fs.WriteLine(fileStream.Length == 0 ? "Text A" : "Text B");
                };
                fileStream.Close();
            }
            catch (IOException)
            {
                done = false;

            }

        }

How to insert data into a text file if the data doesn't exist already (Python)

You were pretty close, but because you open the file to append to it, it starts with the file pointer at the end. You need to seek to the start to read its contents again:

def writeSite(site):
    file = open("websites.txt", 'a+')
    file.seek(0)

    # print(site)

    if site in file.read():
        return

    file.write(site + "\n")
    file.close()

However, keep in mind that site in file.read() is very crude.

For example, imagine you already have 'http://somesite.com/page/' in the file but now you want to add 'http://somesite.com/' - the URL as a whole is not in the file, but your test will find it.

If you want to check whole lines (and be sure you deal with the file nicely), this would be better:

def writeSite(site):
    site += '\n'
    with open("websites.txt", 'a+') as f:
        f.seek(0)
        if site in f.readlines():
            return
        f.write(site)

It adds a newline to the name of the site to separate the URLs in the file and uses readlines to make use of that fact to check for the whole URL. Using with ensures the file always gets closed.

And since you want to read before writing anyway, you could use 'r+' as a mode, and skip the seek - but only if you can be sure the file already exists. I assume you chose 'a+' because that isn't the case.

(in case you worry that this changes the value of site - that's only true for the parameter inside the function. Whatever value you passed in outside the function will remain unaffected)

Create File If File Does Not Exist

You can simply call

using (StreamWriter w = File.AppendText("log.txt"))

It will create the file if it doesn't exist and open the file for appending.

Edit:

This is sufficient:

string path = txtFilePath.Text;               
using(StreamWriter sw = File.AppendText(path))
{
  foreach (var line in employeeList.Items)                 
  {                    
    Employee e = (Employee)line; // unbox once
    sw.WriteLine(e.FirstName);                     
    sw.WriteLine(e.LastName);                     
    sw.WriteLine(e.JobTitle); 
  }                
}     

But if you insist on checking first, you can do something like this, but I don't see the point.

string path = txtFilePath.Text;               

using (StreamWriter sw = (File.Exists(path)) ? File.AppendText(path) : File.CreateText(path))                 
{                      
    foreach (var line in employeeList.Items)                     
    {                         
      sw.WriteLine(((Employee)line).FirstName);                         
      sw.WriteLine(((Employee)line).LastName);                         
      sw.WriteLine(((Employee)line).JobTitle);                     
    }                  
} 

Also, one thing to point out with your code is that you're doing a lot of unnecessary unboxing. If you have to use a plain (non-generic) collection like ArrayList, then unbox the object once and use the reference.

However, I perfer to use List<> for my collections:

public class EmployeeList : List<Employee>

open() in Python does not create a file if it doesn't exist

You should use open with the w+ mode:

file = open('myfile.dat', 'w+')

Create a .txt file if doesn't exist with user inputted data

Here is an example of how to store files to the logged in users My Documents folder on windows.

You can modify the AppendUserFile function to support other file modes. This version will open the file for Appending if it exists, or create it if it doesn't exist.

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication4
{
    class Program
    {
        static void Main(string[] args)
        {
            AppendUserFile("example.txt", tw =>
            {
                tw.WriteLine("I am some new text!");
            });

            Console.ReadKey(true);
        }

        private static bool AppendUserFile(string fileName, Action<TextWriter> writer)
        {
            string path = System.Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
            if (!Directory.Exists(path))
                Directory.CreateDirectory(path);
            string filePath = Path.Combine(path, fileName);
            FileStream fs = null;
            if (File.Exists(filePath))
                fs = new FileStream(filePath, FileMode.Append, FileAccess.Write, FileShare.Read);
            else
                fs = new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.Read);
            using (fs)
            {
                try
                {
                    TextWriter tw = (TextWriter)new StreamWriter(fs);
                    writer(tw);
                    tw.Flush();
                    return true;
                }
                catch
                {
                    return false;
                }
            }
        }
    }
}

Text Files, and New Lines

You can use replace:

def create():
    path = input("What file would you like to create: ")
    output_file = open(path, 'x')
    text = input("What would you like to write? ")
    output_file.write(text.replace('\\n', '\n'))
    output_file.close()
def append():
    path = input("What file would you like to append: ")
    output_file = open(path, 'a')
    text = input("What would you like to write?")
    output_file.writelines(text.replace('\\n', '\n'))
    output_file.close()
write = input("Would you like to write something today, or edit? ")
if write == "Write":
    create()
if write == "Edit":
    append()

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