PYTHON Script not using OS Commands

Question

Within a UBUNTU VM, using GNS3 I created code that is an attempt to after the user's input perform one of 3 different outcomes, however, the if statements don't work, the python files can't be found which I was trying to point to this the cd/home.. command. And the curl commands are apparently the incorrect syntax even though that is what I would enter for them to work. please help me out and get this working.

enter image description here

This is what I tried:

#!/usr/bin/python3
import os
import subprocess
Code = input("Enter RYU, ONOS or CURL:")
print("Command entered was: " + Code)
if input == 'RYU':
 os.system('rest_router.py')
 os.system('gui_topology.py')
elif input == "ONOS":
 os.system('sudo /opt/onos/bin/onos-service start')

• Michael M.: Please do not upload images of code/data/errors when asking a question.
• chepner: You don't need curl for something this simple; just use something like urllib.request or the third-party requests library.
• Amadan: It is also better to import Python code (import rest_router then use its code) than spawn a whole new Python interpreter with os.system('rest_router.py').

Answer 1

You are using single quotes to quote something that already has single quotes. By doing so, what should be an opening quote in your curl command is now effectively a closing quote in your Python, and Python doesn't understand why there is now a random ( there where Python code should continue.

I underlined what is quoted in the following examples. Note that even syntax highlighting in most any editor (and also here on Stack Overflow) is helping you see what is inside a string and what is not, colouring them differently (though syntax highlighting can be fallible):

echo 'foo' bar
 ---

But:

os.system('echo 'foo' bar')
 ----- ----

To fix, you can escape the inner quotes, so Python treats them as any regular character inside the string:

os.system('echo \'foo\' bar')
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Or you can change the outer quotes. Python has several sets of quotes; you can't use ' or " since you're already using both of them inside the string, but you can use ''' or """:

os.system('''echo 'foo' bar''')
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