CODEWITHSUNDEEP
python-3.4
Darth Vagrant
Darth Vagrant

Reputation: 139

Use string in subprocess

I've written Python code to compute an IP programmatically, that I then want to use in an external connection program.

I don't know how to pass it to the subprocess:

import subprocess
from subprocess import call

some_ip = "192.0.2.0"  # Actually the result of some computation,
                       # so I can't just paste it into the call below.

subprocess.call("given.exe -connect  host (some_ip)::5631 -Password")

I've read what I could and found similar questions but I truly cannot understand this step, to use the value of some_ip in the subprocess. If someone could explain this to me it would be greatly appreciated.

Upvotes: 1

Views: 249

Answers (1)

das-g
das-g

Reputation: 9994

If you don't use it with shell=True (and I don't recommend shell=True unless you really know what you're doing, as shell mode can have security implications) subprocess.call takes the command as an sequence (e.g. a list) of its components: First the executable name, then the arguments you want to pass to it. All of those should be strings, but whether they are string literals, variables holding a string or function calls returning a string doesn't matter.

Thus, the following should work:

import subprocess

some_ip = "192.0.2.0"  # Actually the result of some computation.

subprocess.call(
    ["given.exe", "-connect",  "host", "{}::5631".format(some_ip), "-Password"])
  • I'm using str's format method to replace the {} placeholder in "{}::5631" with the string in some_ip.

  • If you invoke it as subprocess.call(...), then

    import subprocess

    is sufficient and

    from subprocess import call

    is unnecessary. The latter would be needed if you want to invoke the function as just call(...). In that case the former import would be unneeded.

Upvotes: 1

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