I see one python script start with
#!%{__python34}
from __future__ import unicode_literals
# Whether we're Python 2
I guess __python34 is used to get the path of python2 or python 3.4, but it does not seem work, as the output message says that the file does not exist...
Thanks.
I believe it is a technique known as "templating" (%{var} is used for instance in the template engine used by RPM as we can see in this example, see the .specfile especially). And a lot of these templating engine exists, Jinja2, Mako and so on and so forth (a more exhaustive list can be found here)
Now let's use Jinja2 to create a simple example, the first thing we create is a template (let's put it in a templates folder to follow the convention), let's call it, python_script_tmpl:
#!{{ python }}
def main():
print("It works")
Now let's create an init (empty script) to create an environment to use with Jinja2.
Now you should have a structure like:
myapp/
__init__.py
templates/
python_script_tmpl
Let's start a shell in the the my_app directory, and run the following line (doc to install jinja2):
from jinja2 import Environment, PackageLoader
env = Environment(loader=PackageLoader("__init__", "templates")) #use the blank __init__ script to init the environment, and the templates folder to load templates
tmpl = env.get_template("python_script_tmpl") #load the template
tmpl.stream(python="/usr/bin/env python3").dump("python_script.py") #create from the template a script called python_script.py
And now at the root of my_app you should have the script python_script.py and it should look like:
#!/usr/bin/env python3
def main():
print("It works")
With the final folder structure:
myapp/
__init__.py
python_script.py
templates/
python_script_tmpl
Assuming the shebang and the env is correctly configured you can run the script without an issue. (albeit not a pretty useful script)
Now what's the point of templating?
If you have to repeat parts a lot of time, (for example the shebang), and that you have to modify it, then you'd have to modify it for every file where it appears, if you use a template, you just have to modify the variable once and inject it. That's a straightforward advantage of templating.
P.S: As @CharlesDuffy mentions, this script is probably extracted from a RPM package, so except for learning purposes, or repackaging, I would suggest you use the rpm command line tool to run the whole package.
