Develop Reference

FileNotFound Exception Raised When Reading Using No Path [duplicate]

My book states:
Every program that runs on your computer has a current working directory, or cwd. Any filenames or paths that do not begin with the root folder are assumed to be under the current working directory
As I am on OSX, my root folder is /. When I type in os.getcwd() in my Python shell, I get /Users/apple/Documents. Why am I getting the Documents folder in my cwd? Is it saying that Python is using Documents folder? Isn't there any path heading to Python that begins with / (the root folder)? Also, does every program have a different cwd?

Every process has a current directory. When a process starts, it simply inherits the current directory from its parent process; and it's not, for example, set to the directory which contains the program you are running.
For a more detailed explanation, read on.
When disks became large enough that you did not want all your files in the same place, operating system vendors came up with a way to structure files in directories. So instead of saving everything in the same directory (or "folder" as beginners are now taught to call it) you could create new collections and other new collections inside of those (except in some early implementations directories could not contain other directories!)
Fundamentally, a directory is just a peculiar type of file, whose contents is a collection of other files, which can also include other directories.
On a primitive operating system, that was where the story ended. If you wanted to print a file called term_paper.txt which was in the directory spring_semester which in turn was in the directory 2021 which was in the directory studies in the directory mine, you would have to say
print mine/studies/2021/spring_semester/term_paper.txt
(except the command was probably something more arcane than print, and the directory separator might have been something crazy like square brackets and colons, or something;
lpr [mine:studies:2021:spring_semester]term_paper.txt
but this is unimportant for this exposition) and if you wanted to copy the file, you would have to spell out the whole enchilada twice:
copy mine/studies/2021/spring_semester/term_paper.txt mine/studies/2021/spring_semester/term_paper.backup
Then came the concept of a current working directory. What if you could say "from now on, until I say otherwise, all the files I am talking about will be in this particular directory". Thus was the cd command born (except on old systems like VMS it was called something clunkier, like SET DEFAULT).
cd mine/studies/2021/spring_semester
print term_paper.txt
copy term_paper.txt term_paper.backup
That's really all there is to it. When you cd (or, in Python, os.chdir()), you change your current working directory. It stays until you log out (or otherwise exit this process), or until you cd to a different working directory, or switch to a different process or window where you are running a separate command which has its own current working directory. Just like you can have your file browser (Explorer or Finder or Nautilus or whatever it's called) open with multiple windows in different directories, you can have multiple terminals open, and each one runs a shell which has its own independent current working directory.
So when you type pwd into a terminal (or cwd or whatever the command is called in your command language) the result will pretty much depend on what you happened to do in that window or process before, and probably depends on how you created that window or process. On many Unix-like systems, when you create a new terminal window with an associated shell process, it is originally opened in your home directory (/home/you on many Unix systems, /Users/you on a Mac, something more or less like C:\Users\you on recent Windows) though probably your terminal can be configured to open somewhere else (commonly Desktop or Documents inside your home directory on some ostensibly "modern" and "friendly" systems).
Many beginners have a vague and incomplete mental model of what happens when you run a program. Many will incessantly cd into whichever directory contains their script or program, and be genuinely scared and confused when you tell them that you don't have to. If frobozz is in /home/you/bin then you don't have to
cd /home/you/bin
./frobozz
because you can simply run it directly with
/home/you/bin/frobozz
and similarly if ls is in /bin you most definitely don't
cd /bin
./ls
just to get a directory listing.
Furthermore, like the ls (or on Windows, dir) example should readily convince you, any program you run will look in your current directory for files. Not the directory the program or script was saved in. Because if that were the case, ls could only produce a listing of the directory it's in (/bin) -- there is nothing special about the directory listing program, or the copy program, or the word processor program; they all, by design, look in the current working directory (though again, some GUI programs will start with e.g. your Documents directory as their current working directory, by design, at least if you don't tell them otherwise).
Many beginners write scripts which demand that the input and output files are in a particular directory inside a particular user's home directory, but this is just poor design; a well-written program will simply look in the current working directory for its input files unless instructed otherwise, and write output to the current directory (or perhaps create a new directory in the current directory for its output if it consists of multiple files).
Python, then, is no different from any other programs. If your current working directory is /Users/you/Documents when you run python then that directory is what os.getcwd() inside your Python script or interpreter will produce (unless you separately os.chdir() to a different directory during runtime; but again, this is probably unnecessary, and often a sign that a script was written by a beginner). And if your Python script accepts a file name parameter, it probably should simply get the operating system to open whatever the user passed in, which means relative file names are relative to the invoking user's current working directory.
python /home/you/bin/script.py file.txt
should simply open(sys.argv[1]) and fail with an error if file.txt does not exist in the current directory. Let's say that again; it doesn't look in /home/you/bin for file.txt -- unless of course that is also the current working directory of you, the invoking user, in which case of course you could simply write
python script.py file.txt
On a related note, many beginners needlessly try something like
with open(os.path.join(os.getcwd(), "input.txt")) as data:
...
which needlessly calls os.getcwd(). Why is it needless? If you have been following along, you know the answer already: the operating system will look for relative file names (like here, input.txt) in the current working directory anyway. So all you need is
with open("input.txt") as data:
...
One final remark. On Unix-like systems, all files are ultimately inside the root directory / which contains a number of other directories (and usually regular users are not allowed to write anything there, and system administrators with the privilege to do it typically don't want to). Every relative file name can be turned into an absolute file name by tracing the path from the root directory to the current directory. So if the file we want to access is in /home/you/Documents/file.txt it means that home is in the root directory, and contains you, which contains Documents, which contains file.txt. If your current working directory were /home you could refer to the same file by the relative path you/Documents/file.txt; and if your current directory was /home/you, the relative path to it would be Documents/file.txt (and if your current directory was /home/you/Music you could say ../Documents/file.txt but let's not take this example any further now).
Windows has a slightly different arrangement, with a number of drives with single-letter identifiers, each with its own root directory; so the root of the C: drive is C:\ and the root of the D: drive is D:\ etc. (and the directory separator is a backslash instead of a slash, although you can use a slash instead pretty much everywhere, which is often a good idea for preserving your sanity).

Your python interpreter location is based off of how you launched it, as well as subsequent actions taken after launching it like use of the os module to navigate your file system. Merely starting the interpreter will place you in the directory of your python installation (not the same on different operating systems). On the other hand, if you start by editing or running a file within a specific directory, your location will be the folder of the file you were editing. If you need to run the interpreter in a certain directory and you are using idle for example, it is easiest to start by creating a python file there one way or another and when you edit it you can start a shell with Run > Python Shell which will already be in that directory. If you are using the command line interpreter, navigate to the folder where you want to run your interpreter before running the python/python3/py command. If you need to navigate manually, you can of course use the following which has already been mentioned:
import os
os.chdir('full_path_to_your_directory')

This has nothing to do with osx in particular, it's more of a concept shared by all unix-based systems, and I believe Windows as well. os.getcwd() is the equivalent of the bash pwd command - it simply returns the full path of the current location in which you are in. In other words:
alex#suse:~> cd /
alex#suse:/> python
Python 2.7.12 (default, Jul 01 2016, 15:34:22) [GCC] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> os.getcwd()
'/'
It depends from where you started the python shell/script.

Python is usually (except if you are working with virtual environments) accessible from any of your directory. You can check the variables in your path and Python should be available. So the directory you get when you ask Python is the one in which you started Python. Change directory in your shell before starting Python and you will see you will it.

os.getcwd() has nothing to do with OSX in particular. It simply returns the directory/location of the source-file. If my source-file is on my desktop it would return C:\Users\Dave\Desktop\ or let say the source-file is saved on an external storage device it could return something like G:\Programs\. It is the same for both unix-based and Windows systems.

How to find path to current .py file in Spyder (Anaconda)?

Set-up
I run a script on my computer, located in the directory Users/path/to/my/script.py.
In the script, I use the path to the script, e.g.,
sub_path = 'Users/path/to/my/'
os.chdir(sub_path + 'other_script/')
As you can see, I define sub_path in the code 'manually'.
Problem
I don't want to define the sub_path manually, I'd rather have Python do it for me.
I'm looking for something similar to the code I use to obtain the current working directory: os.getcwd(), but then a code to obtain the directory of the current file.
I mainly find answers similar to this one, which says,
os.path.abspath(os.path.dirname(__file__))
but in the Spyder & Anaconda set-up, this generates a NameError: name '__file__' is not defined.
What can I do?

You if you want to move back one folder/directory you use the .. in your file path.
os.chdir('../other_scripts/')
will work. You may fine it helpful to view this or the wiki.
If you want to move from where you currently are you can use './new_dir/'. If you want to automate how to find other files you may want to read here which says to use os.walk. This may be the same question.

Mark8888 pointed out to run the whole script (run file (F5)) instead of just pieces of the script
this way multiple approaches should work to get the script file location and change the current working directory
import os
# directory of script file
print(os.path.abspath(os.path.dirname(__file__)))
# change current working directory
os.chdir(os.path.abspath(os.path.dirname(__file__)))
# current working directory
print(os.getcwd())
also
import os
import sys
# directory of script file
print(os.path.abspath(os.path.dirname(sys.argv[0])))
# change current working directory
os.chdir(os.path.abspath(os.path.dirname(sys.argv[0])))
# current working directory
print(os.getcwd())

I add the following lines to any script I run in case I need to access data relative to the location of the script
import sys
script = sys.argv[0]
print(script)
'C:/SomeFolder/A_Subfolder/CurrentlyRunningScript.py' # changed obviously

First, save your Jupyter Notebook. Second, locate the directory your Jupyter Notebook is stored in. Thirdly, ensure that your Jupyter Notebook and CSV file are in the same place.

How do I run python file without path?

To avoid type in long path name, I am trying to create a folder to put all my .py file in. And I want it to be some sort of "default" folder that every time I run .py file, the system will search this folder to look for that file.
One solution i figured, is to put my .py file in those module folders like "python\lib", and I can call python -m filename.
But I do not want to make a mess in the lib folder.
Is there any other ways to do it? Thanks!

I'm assuming you're running Python on Windows (the '\' backslash is my only clue). If so, I think you've got at least one reasonable option.
Create a python_run.bat file similar to this:
#ECHO OFF
REM *** MODIFY THE NEXT LINE TO SPECIFY THE LOCATION OF YOUR SCRIPTS ***
SET SCRIPT_DIR=C:\Path\To\Scripts
REM *** MODIFY THE NEXT LINE TO SPECIFY THE LOCATION OF YOUR PYTHON.EXE ***
SET PYTHON_BIN=C:\Python27\python.exe
PUSHD %SCRIPT_DIR%
%PYTHON_BIN% %*
POPD
Then make sure the folder where the python_run.bat is located is in your PATH environment variable. So if the script lives in C:\Path\To\Scripts\python_run.bat, you'd make sure your PATH environment variable had C:\Path\To\Scripts in it.
Then you simply have to type the following to execute any script located in your SCRIPT_DIR.
python_run my_cool_script.py --foo=bar
And it will result in running the following command as if you were already inside your scripts folder:
C:\Python27\python.exe my_cool_script.py --foo=bar

for example: first type
sys.path.append("/home/xxx/your_python_folder/")
then you can import your own .py file

It's not possible to do that without path. The only thing that you can is putting all of modules that you want to use in the same directory, you don't have to put them python\lib , you can put them in a folder on your desktop for example.Then run your scripts in that folder but, always be sure starting scripts with #!/usr/bin/env python.

How can I make my Python script a system command and run it easily in any directory in Windows?

I am a Python rookie and I learn Python3.3 in Windows.
I wrote my first script, a script to rename files with incremental filenames. But by now, I had to copy my rename.py script to the directory I want to change the files names and run Python rename.py. It is not a very fancy way to use.
I can improve my code and pass the target directory to run my script in origin directory like Python rename.py .../TargetDir, but I have to copy the directory everytime.
So I want to make my script a system command, then I would only type rename in cmd.exe in the directory I want to rename a bunch of files. How can I approach this.

For this purpose, you'll want to use doskey, which allows you to set aliases for commands.
You use it like this:
doskey macroName=macroDefinition
So you would want to write something like this:
doskey rename=Python rename.py .
Where the . stands for the directory you're currently in. (I wasn't exactly clear on what you wanted -- the way I read your question was that you just want to cd into the directory where you want to rename a bunch of files, then run the script.)

Use sys.argv to get the command line arguments. For example test.py:
import os
import sys
path = sys.argv[1]
print(os.listdir(path))
and then you can create a batch file which should placed in a folder that belongs to the PATH variable. In order to do so, create a text document with the following contents and save it as ListDir.bat. Copy the ListDir.bat to either your python folder, or Windows folder (both should be in your PATH)
ListDir.bat:
python C:\test.py "%CD%"
PAUSE
The %CD% refers to the current directory in the windows prompt. So assuming the python script test.py is in C:\ the first line executes the test.py script with the argument current directory.
I used PAUSE to get user input before completing the script, you could choose not to.
After you save the ListDir.bat file. You can navigate to the folder you want to use it in, and just call ListDir

open() function python default directory

I'm new and I have no idea where the default directory for the open() function is.
For example open('whereisthisdirectory.txt','r')
Can someone advise me? I've tried googling it (and looking on stackoverflow) and even putting a random txt file in so many folders but I still can't figure it out. Since I'm beginning, I want to learn immediately rather than type "c:/directory/whatevevr.txt" every time I want to open a file. Thanks!
Ps my python directory has been installed to C:\Python32 and I'm using 3.2

os.getcwd()
Shows the current working directory, that's what open uses for for relative paths.
You can change it with os.chdir.

If you working on Windows OS first type
import os
then type
os.getcwd()
and it should print the current working directory.

The answer is not python-specific. As with programs written in any other language, the default directory is whatever your operating system considers the current working directory. If you start your program from a command prompt window, the CWD will be whatever directory you were in when you ran the program. If you start it from a Windows menu or desktop icon, the CWD is usually defined alongside the program's path when creating the icon, or else falls back to some directory that Windows uses in the absence of that information.
In any case, your program can query the current working directory by calling os.getcwd().

The default location is the CWD (Current Working Directory), so if you have your Python script in c:\directory and run it from there, if you call open() it will attempt to open the file specified in that location.

First, you must import:
import os
Then to print the current working directory:
os.getcwd()
If you want to change the current working directory:
os.chdir('your_complete_required_path')

create the .txt file in the directory where u have kept .py file(CWD) and run the .py file.

The open() function for file always creates files in the current working directory. The best way to find out your current working directory is to find three lines of small code:
import os
current_working_directory = os.getcwd()
print(current_working_directory)
Run this above code and you will get your current working directory where open() function creates a new file. Good Luck!

If you’re running your script through an interpreter (i.e pycharm, VSCode etc) your Python file will be saved, most likely, in my documents (at least in VSCode, in my personal experience) unless you manually save it to a directory of your choosing before you run it. Once it is saved, the interpreter will then use that as you current directory so any saves your Python script will create will also automatically go there unless you state otherwise.

it depends on how you run it from the terminal
like this, it is going to look in your home directory
C:\Users\name>python path\file.py
and like this, it is going to look next to your file
C:\Users\name>cd path
C:\Users\name\path>python file.py