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Python and shell scripts interaction library

Project description

ShellWrap

This small module allows you to write shell commands inside your Python program. This module is not a replacement for subprocess or any of the Python modules that are a high level abstractions on top of program and command execution or shell interaction. On the contrary ShellWrap executes a shell interpreter that will live as long as your Python script is running. A simple function decorator will allow Python function to have a shell script body. These functions will be augmented and passed to the shell interpreter. Let's start with some examples:

Example: Check if a site is UP

This example will regularily check for the given site to respond with a 200, Ok. This is handy when you are waiting for a site to become responsive or waiting for it to boot up.

import time
from shellwrap import ShellWrap
shell = ShellWrap('bash').get_shell()

@shell()
def is_the_site_up(url):
    'curl -sL -m 2 -w "%{http_code}" "${url}" -o /dev/null | grep -q 200'

while is_the_site_up('https://google.com').fails():
    time.sleep(4)

You just have to annotate a function with the @shell decorator and it will be parsed and each line (a loose string) will be fed into a running bash interpreter.

Example: Getting results

The return value of calling a function annotated with @shell is a Result type that has a few convenience functions:

  • Result().fails() returns True if the command failed (its exitcode is != 0)
  • Result().success() returns True if the command succeeded (equivalent to not .fails())
  • Result().exitcode contains the exit code of the last command executed in your function
  • Result().stdout contains all the output of the execution of your function

Example: Passing arguments to functions

You can define a function with arguments, like is_the_site_up above and these arguments will be converted into variables for the execution of your function, inside the bash environment.

@shell()
def passing_arguments_to_funcs(arg0, arg1, someother):
    'echo "got $arg0 and $arg1"'
    'echo "and also $someother"'

result = passing_arguments_to_funcs('hello', 10, 'love you bash')

assert(result.exitcode == 0)

This will result in the following being displayed:

got hello and 10
and also I love you bash

Example: Timeouts

You might have a process that you only want to execute for a few seconds, for it to return. If the process get stuck, you want to kill it and continue with your life. This is possible with ShellWrap by using the timeout parameter in your decorator.

@shell(timeout=3)
def will_timeout_in_3_secs(mymessage):
    'sleep 1'
    'echo "${mymessage}"'
    'sleep 1'

result = will_timeout_in_3_secs('Only patience will reveal the truth.')
if result.success():
    print('Your patience will be rewarded')

In the last example, we will give the decorated function 10 seconds to run, and we know it will take around 8 seconds to complete. The first run will succeed, but if you change the timeout parameter to 7, the function will fail. Will still print the message passed as an argument to the function (the echo was called), but the function will result in an error, as it was killed because of the timeout.

Contributing to the project

Please see our Contribution page!

License

The project is distributed under the MIT license.

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0.1

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