I am using Python 2.7
I have interactive Python script, named A, written using Cmd module.
However, sometimes there is a need to activate script A from other Python scripts.
It also could be nice if the interactive script A wouldn't exit in between commands given to them.
I tried to search for solutions and I found couple here
One is to pass a file from which the interactive script will read commands. It works well for me but it is not much liked.
Another is to use echo which doesn't work for me (still trying).
I wonder whether there are other solutions.....
Related
1) I am new to Python and love to learn its core. I have downloaded the python software package and discovered the python.exe application inside. I double clicked it and a balck and white window popped up.
Should I call it a python Interpreter or python Shell?
2) I am learning python online. I came across the terms python tty, python shell and python interpreter. I am satisfied by calling that screen inside the window as a tty(TeleTYpewriter) because we could use only keyboard to work inside and no mouse. But actually that screen has got some intelligence responding to our request. Is python tty an apt term for it?
3) In UNIX, shell is an user interface and command line interpreter, so does python interpreter and python shell are the same.
Python shell lets you use the Python interpreter in interactive mode, just as an OS shell, such as bash, lets you use the OS in interactive mode. You can use the Python interpreter in script mode or batch mode wherein you let the interpreter execute all lines of code in one sequence. It is comparable to writing shell scripts (or batch files in Microsoft Windows).
In your case the screenshot is of a python "shell".
You shouldn't really pay attention to this distinction because in the end everything runs through the python interpreter be it in interactive mode or not.
It is both the python shell and the python interpreter. The shell is where you write your code directly in the CLI, whereas the interpreter is the program that will interpret your code and execute it. Therefore, the interpreter is called in the shell when you write some code, it may also be called when you execute some python code directly from a file.
The customary term for the interactive Python shell is the Python REPL. Many modern interpreters enter a Read-Eval-Print-Loop when you run them interactively, and this term has stuck.
The program which interprets and executes your Python code is the Python interpreter; it can act as a shell, as described above, or run silently and just execute your Python code without any visible user interface of its own, like when you run a script of yours with
python scriptname.py
I am new to Python and I am wondering how can I keep the modules and data from a script I run from the Python shell?
For example: I have the script helloworld.py and it contains:
import numpy as donkey
a = 55
Then I want to run that script from my Python shell:
execfile('helloworld.py')
However, if I then try to call for 'a' or 'donkey', they are not found.
How can I fix that?
I will assume you are using IDLE. IDLE is not a shell in Unix sense. So there is not a direct equivalent of the bash shell . ~/.bash_profile.
Instead I edit the file and then use F5 Run Module. All my variables, functions, and classes get loaded. I can use the interpretive shell to manipulate. However, if I run another module, I reset the environment, losing the first module's definitions.
The execfile() approach is limited to Python 2 as noted here:
How to run a Python script from IDLE command line?
I am using python.exe.
I tried:
C:/myfile.py
python C:/myfile.py
python "C:/myfile.py"
It always says "invalid syntax". The code is this one:
https://github.com/paulnasca/paulstretch_python/blob/master/paulstretch_stereo.py#L150
So not sure if the file has bugs or I am doing something wrong.
Your screenshot shows that you are already in the Python interpreter. Trying to run python again will result in an error. Exit the interpreter by hitting CtrlD. Make sure you have downloaded the complete paulstretch_stereo.py file. Put the file in the same directory as the files you want to process. Then, from the Windows command line, run python paulstretch_stereo.py --help and the program's options should print out.
By the way, make sure you have NumPy and SciPy installed, otherwise the program won't run.
What you get when you run python.exe directly is called the interactive interpreter.
The usual way to run a python module is simply providing it as a command-line option to the python process:
python C:/myfile.py
This command is provided from your command-line, not from the interactive interpreter.
I'd like to call a separate non-child python program from a python script and have it run externally in a new shell instance. The original python script doesn't need to be aware of the instance it launches, it shouldn't block when the launched process is running and shouldn't care if it dies. This is what I have tried which returns no error but seems to do nothing...
import subprocess
python_path = '/usr/bin/python'
args = [python_path, '&']
p = subprocess.Popen(args, shell=True)
What should I be doing differently
EDIT
The reason for doing this is I have an application with a built in version of python, I have written some python tools that should be run separately alongside this application but there is no assurance that the user will have python installed on their system outside the application with the builtin version I'm using. Because of this I can get the python binary path from the built in version programatically and I'd like to launch an external version of the built in python. This eliminates the need for the user to install python themselves. So in essence I need a simple way to call an external python script using my current running version of python programatically.
I don't need to catch any output into the original program, in fact once launched I'd like it to have nothing to do with the original program
EDIT 2
So it seems that my original question was very unclear so here are more details, I think I was trying to over simplify the question:
I'm running OSX but the code should also work on windows machines.
The main application that has a built in version of CPython is a compiled c++ application that ships with a python framework that it uses at runtime. You can launch the embedded version of this version of python by doing this in a Terminal window on OSX
/my_main_app/Contents/Frameworks/Python.framework/Versions/2.7/bin/python
From my main application I'd like to be able to run a command in the version of python embedded in the main app that launches an external copy of a python script using the above python version just like I would if I did the following command in a Terminal window. The new launched orphan process should have its own Terminal window so the user can interact with it.
/my_main_app/Contents/Frameworks/Python.framework/Versions/2.7/bin/python my_python_script
I would like the child python instance not to block the main application and I'd like it to have its own terminal window so the user can interact with it. The main application doesn't need to be aware of the child once its launched in any way. The only reason I would do this is to automate launching an external application using a Terminal for the user
If you're trying to launch a new terminal window to run a new Python in (which isn't what your question asks for, but from a comment it sounds like it's what you actually want):
You can't. At least not in a general-purpose, cross-platform way.
Python is just a command-line program that runs with whatever stdin/stdout/stderr it's given. If those happen to be from a terminal, then it's running in a terminal. It doesn't know anything about the terminal beyond that.
If you need to do this for some specific platform and some specific terminal program—e.g., Terminal.app on OS X, iTerm on OS X, the "DOS prompt" on Windows, gnome-terminal on any X11 system, etc.—that's generally doable, but the way to do it is by launching or scripting the terminal program and telling it to open a new window and run Python in that window. And, needless to say, they all have completely different ways of doing that.
And even then, it's not going to be possible in all cases. For example, if you ssh in to a remote machine and run Python on that machine, there is no way it can reach back to your machine and open a new terminal window.
On most platforms that have multiple possible terminals, you can write some heuristic code that figures out which terminal you're currently running under by just walking os.getppid() until you find something that looks like a terminal you know how to deal with (and if you get to init/launchd/etc. without finding one, then you weren't running in a terminal).
The problem is that you're running Python with the argument &. Python has no idea what to do with that. It's like typing this at the shell:
/usr/bin/python '&'
In fact, if you pay attention, you're almost certainly getting something like this through your stderr:
python: can't open file '&': [Errno 2] No such file or directory
… which is exactly what you'd get from doing the equivalent at the shell.
What you presumably wanted was the equivalent of this shell command:
/usr/bin/python &
But the & there isn't an argument at all, it's part of sh syntax. The subprocess module doesn't know anything about sh syntax, and you're telling it not to use a shell, so there's nobody to interpret that &.
You could tell subprocess to use a shell, so it can do this for you:
cmdline = '{} &'.format(python_path)
p = subprocess.Popen(cmdline, shell=True)
But really, there's no good reason to. Just opening a subprocess and not calling communicate or wait on it already effectively "puts it in the background", just like & does on the shell. So:
args = [python_path]
p = subprocess.Popen(args)
This will start a new Python interpreter that sits there running in the background, trying to use the same stdin/stdout/stderr as your parent. I'm not sure why you want that, but it's the same thing that using & in the shell would have done.
Actually I think there might be a solution to your problem, I found a useful solution at another question here.
This way subprocess.popen starts a new python shell instance and runs the second script from there. It worked perfectly for me on Windows 10.
You can try using screen command
with this command a new shell instance created and the current instance runs in the background.
# screen; python script1.py
After running above command, a new shell prompt will be seen where we can run another script and script1.py will be running in the background.
Hope it helps.
I'm new to Python programming.
My question is where to write python programs in linux--
in terminal or
any writing pad like gedit etc
Should we write one program again and again for running or we should call the program and run it.
After you install Python (it's installed by default on most Linux-es), you have two options:
Terminal. Just type python <ENTER> and you will be taken to the Python interpreter interactive prompt. For anything but the most basic stuff, however, you may want to intall IPython - an alternative interactive prompt that's much better than the default one.
In a file. Save your code into a .py file and run it with python myfile.py
But first and foremost, start by learning Python - the official tutorial is a great place to start. Among other useful information, its chapter 2 discusses how to use the Python interpreter for beginners.
Stackoverflow also has a lot of great resources for learning Python. This question, for example, and many others.
If you are learning, or you are evaluating expressions, you could run Python in terminal, or use IDLE.
But if you are writing large chunks of code, then you should consider using an IDE.
You could either use Geany, or use Eclipse with PyDev. I prefer Eclipse myself.
For running, you can run it using the command python program.py, or just add the line
#!/bin/python
to the beginning of your program, grant it execution permission using chmod, and run it with ./program.py command.