How to recover or modify your PATH variable on Windows

How to Recover or Modify your Path Environment Variable on Windows

When you need to run an executable from the command line, your operative system needs to know where to find it. Otherwise, you get an error like this one:

C:\> ping www.google.com

'ping' is not  recognized as an internal or external command, operable program or batch file.

To fix this, you need to add the directory in which that executable is located to your PATH environment variable.

Warning and disclaimer: don't touch this if you are clueless about what you are doing. The Path variable is used by your operative system even for the most basic of commands, if you delete it or make a mistake, your system could become unstable. I will NOT be held responsible for any damages or consequences whatsoever. 

How to Modify the Path Variable:

If you are not sure if the variable you are looking for is added to your Path or not and you don't want to use the GUI, you can try running cmd.exe and entering this command:

echo %PATH%

1. Right click on 'Computer' and select 'Properties'
2. Go to the Advanced Systems Settings section and select the 'Advanced' tab
3. Click on 'Environment Variables'
4. The Path variable is located on the second list, you might have to scroll down a little (see picture). Select it and click on 'Edit...'
5. When modifying the Path variable, only add exactly what you need and don't remove anything else. When you are done, OK the changes. Make sure that you do not leave any spaces between the semicolons and add a semicolon to your final variable, e.g.:

C:\Windows\system32;C:\Python27;

The Path variable is selected in light blue.

I made a mistake before and nothing works. How do I recover my Path variable?

Follow steps 1-5, but add this variable:

%SystemRoot%\system32;%SystemRoot%;

Make sure that there are no trailing spaces anywhere (check the other variables), and that no variables are missing semicolons. This has been tested on Windows XP 32-bit and Windows 7 64-bit.
If this doesn't work, and you are using a very basic command (I like to test with 'ping'), you should check that the files themselves have not been deleted. Ping is usually located at C:\Windows\System32

Installing the NLTK: Tips and tricks

Installing the NLTK: 

Tips and Tricks

Though the NLTK is a very useful tool aimed at students, sometimes its installation can be a bit tricky. Some people recommend that you use a pre-bundled version such as Enthought, but I have not had the chance to use it yet.These tips might help you if you are having trouble:

• If you are getting an error when trying to install Numpy, NLTK or YAML on a 64-bit version of Windows complaining that Python has not been found, check that you have installed a 32-bit version of Python (x86). Also, bear in mind that you need different downloads for Python 2.x and for Python 3.x. If you are going to use Python 2.x, I recommend that you use Python 2.7.

• I highly recommend that you download and install setuptools and pip. Setuptools includes easy_install, which will make your life so much easier. They can help you when the binaries are defective or outdated. These tools are aimed at simplifying your work when you need to compile from source. To install setuptools, follow the instructions on this link. Pip installation instructions can be found here. Basically, you just download the .py file and run it. 

Warning: To be able to run it, make sure that you have added C:\Python27 (or whatever your Python installation directory is) and C:\Python27\Scripts to your PATH variable. Instructions on how to do this (and how to fix your PATH variable if it is broken) can be found on this post.

•  You won't notice any big changes, but you can check that it worked by trying to install a package such as matplotlib. You need to use Windows' Command Line Interface for this (Start menu>Run>cmd.exe). Just type this on the prompt and hit Return:

pip install matplotlib

or, if you prefer to use easy install:

easy_install matplotlib

You will often see it written as:

sudo easy_install matplotlib

sudo pip install matplotlib

The 'sudo' is meant for Mac and Linux systems, not Windows systems. In order to know if everything went well, open up IDLE and try to import the package you just installed, e.g.:

 >>> import matplotlib 

If Python doesn't complain about a package not being found and simply shows you another line of the prompt, the installation went well. 

• I found that matplotlib, which is used throughout the book to plot graphs, gave some problems after installing from the binaries (it would install correctly but NLTK was having trouble with it), so I finally installed from source. This solved the problem.

• Sometimes pip or easy_install will complain about a lack of vcvarsall.bat.This means that easy_install or pip need a C compiler in order to compile part of the code you asked it to install. To fix this, you need to install Microsoft Visual Studio and add it to your path. These StackOverflow answers should help, but make sure that you know what C compiler your Python version uses, in order to avoid problems (they are not the same).