Subprocesses



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from subprocess import (
    call,
    check_call,
    check_output,
    PIPE,
    STDOUT,
    CalledProcessError,
    Popen,
)

Getting return codes



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print call("true")



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print call("false")



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print check_call("false")



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print check_call("fortune")

Not terribly useful. Where is the output going? Let's take a look at the terminal.

Collecting output



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print check_output("fortune")



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command = ["fortune", "--help"]
print check_output(command)



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try:
    print check_output(command)
except CalledProcessError as e:
    print e.output

Where's the error?

Redirection and Communication



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try:
    print check_output(command, stderr=STDOUT)
except CalledProcessError as e:
    print e.output



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lines = """
foo
bar
baz"""

command = ["grep", "-n", "bar"]

e = Popen(command, stdin=PIPE, stdout=PIPE)

stdout, stderr = e.communicate(lines)

print stdout