Python Subprocess command with quotes and variables

Question

I have a complicated command that I want to run with subprocess. It contains single and double quotes and I want to drop in some variables.

This is the string:

gitlab create_merge_request 5 "{} - New merge request - {}" "{source_branch: '{}', target_branch: 'dev', assignee_id: 1}"  --json

I want to maintain the quotes around the 'New merge request' section (it contains two variables and around the 'source_branch' variable. The curly braces in the 'source_branch' section are also causing problems.

When I format the string like this:

gitLabCreateMerge = ('/usr/local/bin/gitlab create_merge_request 5 ', str(committerUser), ' requested - Automated Merge Request- ', str(reviewerUser), "'{source_branch:", str(branchName), " target_branch: 'dev', assignee_id: 1}' --json")

It looks like this:

('/usr/local/bin/gitlab create_merge_request 5 ', 'alice', ' requested - Automated merge request - joe ', "'{source_branch:", 'testdevbranch', " target_branch: 'dev', assignee_id: 1}' --json")

Can you please use more distinctive values than asdfasd, it will make the question easier to read. Write `committerUser = 'alice'` in the question, for example. — Josh Lee, Apr 27 '17 at 17:04

score 2 · Accepted Answer · edited Apr 27 '17 at 17:20

With subprocess, you're better off passing a list of strings rather than a string to be evaluated by the shell. This way you don't need to worry about balancing your double quotes (and escaping potentially executable values).

The curly braces can be escaped from string formatting by doubling them.

With those two notes in mind, here's what I might do:

committerUser = 'alice'
reviewerUser = 'joe'
branchName = 'testdevbranch'
cmd = ["gitlab",
    "create_merge_request",
    "5",
    f"{committerUser} - New merge request - {reviewerUser}",
    f"{{source_branch: '{branchName}', target_branch: 'dev', assignee_id: 1}}",
    "--json"]
subprocess.Popen(cmd, …)

I'm using Python 3.6's f-strings here, but it could also be done with the str.format() method

"{} - New merge request - {}".format(committerUser, reviewerUser),
"{{source_branch: '{}', target_branch: 'dev', assignee_id: 1}}".format(branchName),

Or explicitly by concatenation, which might be more readable than trying to remember what the double curly braces are for.

committerUser + " - New merge request - " + reviewerUser,
"{source_branch: '" + branchName + "', target_branch: 'dev', assignee_id: 1}",

Thanks for the response. I'm getting an error for one of the lines(sorry about the formatting): f"'{committerUser} - New merge request - {reviewerUser}'", ^ SyntaxError: invalid syntax — Publiccert, Apr 27 '17 at 18:09
Subbing out the two f-string lines for your str.format() lines did the trick. Thank you! — Publiccert, Apr 27 '17 at 18:14

Python Subprocess command with quotes and variables

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