Python is an indisputably popular programming language for programmers who want to create code as quickly and efficiently as possible. However, programmers are sometimes at a loss when it comes to offering similar benefits to end-users. How exactly do you go about shipping Python code in a manner that’s easy to use for the average person? There’s a wide variety of different answers to that question. But the Python shebang interpreter directive is one of the more popular due to its sheer ease of implementation. The following python tutorial will show you what this powerful function is and how to use it.
What Is the Shebang Interpreter Directive?
The directive’s full title makes it sound rather complex or even ominous. But in reality, it’s essentially just a little shorthand inserted at the beginning of a Python script. The additional text helps the operating system understand how to run the script. So, for example, using this system on Linux would mean you could execute Python’s scripts as if they were a binary executable.
A Deeper Dive Into the Directive
Now that you know what the term means, it’s important to delve a little deeper into why it works. The directive’s additional text takes advantage of the fact that Python’s scripts are just plain text files. A command line shell like bash will usually be able to read plain text files. And, likewise, it should have a scripting system like sh which can go through those files on a line-by-line basis.
The directive’s functionality stems from the ability of these systems to understand a few basic messages related to secondary systems like a Python interpreter. The shebang line will tell a shell how to properly execute text files. As long as you use the correct executable permissions on the script then it should launch just like a standard compiled binary. However, it’s important to note that the terminal itself will determine whether or not you can use the directive’s functionality. All Linux systems and Macs should be compatible. But Windows can be a little hit or miss.
If you’re running Python’s scripts through cygwin or a similar emulated terminal then it will work just as it would on Linux. But using the directive’s functionality on a Windows command line is highly dependent on a number of other variables. For example, if you use power shell and the official Python installer then this method should work. But if you’re using a standard Windows cmd then it will probably fail. Unless you installed the Python interpreter through the Windows store. In which case the method might, in fact, work.
In short, Windows can be something of a problem with this particular system. Linux almost always works fine with it, and OSX will usually be OK as well. But even Linux and OSX have individual quirks. This is why you should try to avoid the use of include arguments and the like with this method. OSX and Linux usually treat additional arguments with the shebang identifier differently. And it’s best to avoid fragmenting compatibility even more than it already is by default.
It’s clear that this method doesn’t provide the highest level of compatibility. While you’ll be fine sending scripts to most Unix-like systems it can have issues outside those environments. If you want the highest level of compatibility it’s generally best to create some form of real executable. Something like pyinstaller or PyPy can create more cross-platform solutions with true executable generation. However, the directive’s real strength is speed. It’s incredibly easy to use this method to create something that can be easily run on select systems. And you’re about to discover just how simple the process is.
Implementing the Directive
We can see just how easily implemented the system is by creating a script called test.py with the following code. Keep in mind that this works best on Linux, may work on OSX, and tends to have issues on Windows unless you’re running cygwin or a similar emulated UNIX terminal.
On line 1 we see the shebang line. The first two symbols compose the shebang character. The following text points to the Python launcher. You should note that we explicitly point to python3 rather than python. By using this syntax we essentially create a Python command that bypasses any 2.x interpreter. Where if you weren’t using a numerical indicator it might go to 2.x or 3.x depending on your system’s layout.
This is possible because /usr/bin/env essentially points to a list of environment variables. And from here your system will find which binary is associated with python3. This methodology is also why there’s no need to specify an absolute path for the interpreter. The /usr/bin/env path works as a virtual environment of sorts that correctly links shorthand commands to the full path.
Now try running the script with the standard Python 3 interpreter. For example, by typing python3 test.py on your command line. You’ll probably receive a “permission denied” error message. The error comes about because the script needs an x permission to identify it as executable. You can fix that problem quite easily by typing the following on the command line.
chmod +x test.py
This allows you to invoke scripts directly as long as the shebang syntax is used. So now try typing the following.
The script should execute just as if it were a compiled binary. And you could even email test.py to someone else and expect them to be able to use it on their own system in the same way.