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How to pass arguments to python script? [duplicate]

I know that I can run a python script from my bash script using the following:
python python_script.py
But what about if I wanted to pass a variable / argument to my python script from my bash script. How can I do that?
Basically bash will work out a filename and then python will upload it, but I need to send the filename from bash to python when I call it.

To execute a python script in a bash script you need to call the same command that you would within a terminal. For instance
> python python_script.py var1 var2
To access these variables within python you will need
import sys
print(sys.argv[0]) # prints python_script.py
print(sys.argv[1]) # prints var1
print(sys.argv[2]) # prints var2

Beside sys.argv, also take a look at the argparse module, which helps define options and arguments for scripts.
The argparse module makes it easy to write user-friendly command-line interfaces.

Use
python python_script.py filename
and in your Python script
import sys
print sys.argv[1]

Embedded option:
Wrap python code in a bash function.
#!/bin/bash
function current_datetime {
python - <<END
import datetime
print datetime.datetime.now()
END
}
# Call it
current_datetime
# Call it and capture the output
DT=$(current_datetime)
echo Current date and time: $DT
Use environment variables, to pass data into to your embedded python script.
#!/bin/bash
function line {
PYTHON_ARG="$1" python - <<END
import os
line_len = int(os.environ['PYTHON_ARG'])
print '-' * line_len
END
}
# Do it one way
line 80
# Do it another way
echo $(line 80)
http://bhfsteve.blogspot.se/2014/07/embedding-python-in-bash-scripts.html

use in the script:
echo $(python python_script.py arg1 arg2) > /dev/null
or
python python_script.py "string arg" > /dev/null
The script will be executed without output.

I have a bash script that calls a small python routine to display a message window. As I need to use killall to stop the python script I can't use the above method as it would then mean running killall python which could take out other python programmes so I use
pythonprog.py "$argument" & # The & returns control straight to the bash script so must be outside the backticks. The preview of this message is showing it without "`" either side of the command for some reason.
As long as the python script will run from the cli by name rather than python pythonprog.py this works within the script. If you need more than one argument just use a space between each one within the quotes.

and take a look at the getopt module.
It works quite good for me!

Print all args without the filename:
for i in range(1, len(sys.argv)):
print(sys.argv[i])

Calling a command line utility from Python

I am currently trying to utilize strace to automatically trace a programm 's system calls. To then parse and process the data obtained, I want to use a Python script.
I now wonder, how would I go about calling strace from Python?
Strace is usually called via command line and I don't know of any C library compiled from strace which I could utilize.
What is the general way to simulate an access via command line via Python?
alternatively: are there any tools similar to strace written natively in Python?
I'm thankful for any kind of help.
Nothing, as I'm clueless

You need to use the subprocess module.
It has check_output to read the output and put it in a variable, and check_call to just check the exit code.
If you want to run a shell script you can write it all in a string and set shell=True, otherwise just put the parameters as strings in a list.
import subprocess
# Single process
subprocess.check_output(['fortune', '-m', 'ciao'])
# Run it in a shell
subprocess.check_output('fortune | grep a', shell=True)
Remember that if you run stuff in a shell, if you don't escape properly and allow user data to go in your string, it's easy to make security holes. It is better to not use shell=True.

You can use commands as the following:
import commands
cmd = "strace command"
result = commands.getstatusoutput(cmd)
if result[0] == 0:
print result[1]
else:
print "Something went wrong executing your command"
result[0] contains the return code, and result[1] contains the output.

Python 2 and Python 3 (prior 3.5)
Simply execute:
subprocess.call(["strace", "command"])
Execute and return the output for processing:
output = subprocess.check_output(["strace", "command"])
Reference: https://docs.python.org/2/library/subprocess.html
Python 3.5+
output = subprocess.run(["strace", "command"], caputure_output=True)
Reference: https://docs.python.org/3.7/library/subprocess.html#subprocess.run

accessing python dictionary from bash script

I am invoking the bash script from python script.
I want the bash script to add an element to dictionary "d" in the python script
abc3.sh:
#!/bin/bash
rank=1
echo "plugin"
function reg()
{
if [ "$1" == "what" ]; then
python -c 'from framework import data;data(rank)'
echo "iamin"
else
plugin
fi
}
plugin()
{
echo "i am plugin one"
}
reg $1
python file:
import sys,os,subprocess
from collections import *
subprocess.call(["./abc3.sh what"],shell=True,executable='/bin/bash')
def data(rank,check):
d[rank]["CHECK"]=check
print d[1]["CHECK"]

If I understand correctly, you have a python script that runs a shell script, that in turn runs a new python script. And you'd want the second Python script to update a dictionnary in the first script. That will not work like that.
When you run your first python script, it will create a new python process, which will interpret each instruction from your source script.
When it reaches the instruction subprocess.call(["./abc3.sh what"],shell=True,executable='/bin/bash'), it will spawn a new shell (bash) process which will in turn interpret your shell script.
When the shell script reaches python -c <commands>, it invokes a new python process. This process is independant from the initial python process (even if you run the same script file).
Because each of theses scripts will run in a different process, they don't have access to each other data (the OS makes sure that each process is independant from each other, excepted for specific inter-process communications methods).
What you need to do: use some kind of interprocess mechanism, so that the initial python script gets data from the shell script. You may for example read data from the shell standard output, using https://docs.python.org/3/library/subprocess.html#subprocess.check_output

Let's suppose that you have a shell plugin that echoes the value:
echo $1 12
The mockup python script looks like (I'm on windows/MSYS2 BTW, hence the strange paths for a Linux user):
import subprocess
p = subprocess.Popen(args=[r'C:\msys64\usr\bin\sh.exe',"-c","C:/users/jotd/myplugin.sh myarg"],stdout=subprocess.PIPE,stderr=subprocess.PIPE)
o,e= p.communicate()
p.wait()
if len(e):
print("Warning: error found: "+e.decode())
result = o.strip()
d=dict()
d["TEST"] = result
print(d)
it prints the dictionary, proving that argument has been passed to the shell, and went back processed.
Note that stderr has been filtered out to avoid been mixed up with the results, but is printed to the console if occurs.
{'TEST': b'myarg 12'}

How to import a python file in a bash script ? (to use a python value in my bash script)

I would like to know if it's possible in a bash script to include a python script in order to write (in the bash script) the return value of a funnction I wrote in my python program ?
For example:
my file "file.py" has a function which returns a variable value "my_value" (which represents the name of a file but anyway)
I want to create a bash script which has to be able to execute a commande line like "ingest my_value"
So do you know how to include a python file in a bash script (import ...?) and how is it possible to call a value from a python file inside a bash script ?
Thank you in advance.
Update
Actually, my python file looks like that:
class formEvents():
def __init__(self):
...
def myFunc1(self): # function which returns the name of a file that the user choose in his computeur
...
return name_file
def myFunc2(self): # function which calls an existing bash script (bash_file.sh) in writing the name_file inside it (in the middle of a line)
subprocess.call(['./bash_file.sh'])
if__name__="__main__":
FE=formEvents()
I don't know if it's clear enough but here is my problem: it's to be able to write name_file inside the bash_file.sh
Jordane

The easiest way of doing this is via the standard UNIX Pipeline and your Shell.
Here's an example:
foo.sh:
#!/bin/bash
my_value=$(python file.py)
echo $my_value
file.py:
#!/usr/bin/env python
def my_function():
return "my_value"
if __name__ == "__main__":
print(my_function())
The way this works is simple:
You launch foo.sh
Bash spawns a subprocess and runs python file.py
Python (and the interpretation of file.py) run the function my_function and print it's return value to "Standard Output"
Bash captures the "Standard Output" of the Python process in my_value
Bash then simply echoes the value stored in my_value also to "Standard Output" and you should see "my_value" printed to the Shell/Terminal.

If the python script outputs the return value to the console, you should be able to just do this
my_value=$(command)
Edit: Damn, beat me to it

Alternatively, you can make the bash script process arguments.
#!/usr/bin/bash
if [[ -n "$1" ]]; then
name_file="$1"
else
echo "No filename specified" >&2
exit 1
fi
# And use $name_file in your script
In Python, your subprocess call should be changed accordingly:
subprocess.call(['./bash_file.sh', name_file])

I want to have raw_input and nohup together in python

I am dealing with a large data set and it takes some days to run, therefore I use nohup to run my script in terminal.
This time I need to first get a raw_input from terminal then by nohup, my codes starts running. Any suggestion how I can do that?
so first I need to get input from terminal like this
$ python myprogram.py
enter_input: SOMETHING
then the process should be like this:
$nohup python myprogram.py &
But I want to do this in one step via terminal. I hope my explanation is clear :)

Here's one more option, in case you want to stick with the user-friendly nature of the input box. I did something like this because I needed a password field, and didn't want the user to have to display their password in the terminal. As described here, you can create a small wrapper shell script with input boxes (with or without the -s option to hide), and then pass those variables via the sys.argv solution above. Something like this, saved in an executable my_program.sh:
echo enter_input:
read input
echo enter_password:
read -s password
nohup python myprogram.py $username $password &
Now, running ./my_program.sh will behave exactly like your original python my_program.py

I think you shouldn't your program have read input from stdin, but give it data via its command line.
So instead of
startdata = raw_input('enter_input:')
you do
import sys
startdata = sys.argv[1]
and you start your program with
$ nohup python myprogram.py SOMETHING &
and all works the way you want - if I get you right.

You could make your process fork to the background after reading the input. The by far easier variant, though, is to start your process inside tmux or GNU screen.