I am relatively new to python, so I was wondering if I could call upon python to read a string (or the code it needs to execute) from outside the interactive python shell, similar to how exec() works when within Python.
Basically, I want to know if there is any method to have python read code from the command line or otherwise rather than having to save that code within a 'file.py' or another similar file.
I want to avoid running this: python file.py as I hope to avoid needing a filename.
I was looking around for a solution and found Execute python commands passed as strings in command line using python -c and Python - How do I pass a string into subprocess.Popen (using the stdin argument)?. The first answer seems to be what I might want, but I lack in the knowledge department of how to pass the string into stdin, so I would be grateful if someone could better explain that method if it is the correct answer. The second link was what I found when looking up about stdin, and looked promising, but upon execution I realized that, from my understanding, I still need some sort of file name for subprocess.
I was planning to use this in order to be used in Jupyter Notebook, or any similar program so when I run one data cell, it is able to be executed in Python or return the error message, but to first do that I have to find out how to reference the language I want without needing a file name. Thank you for your time and consideration!
2 Answers
Its a bit unclear exactly what you want to to with this but here is hello world using the command option (-c) from the command line without piping it in. This just runs the string passed as if it was in the python interpreter or in a script.
python -c "print('hello world')"
If you really want to run code from stdin you could use something like this:
echo "for i in range(100):\n\tprint(i)" | python -c "import sys;print('hello world');exec(''.join([item for item in sys.stdin]))"
There is more on how to use the command line tool in the man page or in the python documentation.
2 Comments
A_Newbie
I appreciate the help, but I was looking for an answer that could provide more than one string. I found that method in stackoverflow.com/questions/10768584/… but as the first response stated, it cannot print more than one string.
python -c "x = 'hello', print(x)" doesn't seem to work. Do you know how to pass python code into stdin, as apparently that is the answer but I am unfamiliar with itSimon Hobbs
that won't work but python -c "x = 'hello';print(x)" does
You can use the following:
python -c "my_var = 'my name is john';print(my_var)"
Note that
1) using ; you seperate the commands.
2) you need to use " " and inside to type the commands.
def exec_py(code): proc = subprocess.Popen(["python", 'f'], stdin = subprocess.PIPE, stdout=STDOUT, stderr=subprocess.PIPE, shell=False) return_code = proc.wait() proc.stdin.write('code') out = proc.stdout.read() err = proc.stderr.read() if (err): return(err.decode("utf-8")) else: return(out.decode("utf-8"))where code would be given by running an individual cell in Jupyter, but once again it requires a file named 'f' that I cannot provide.python.