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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def is_process_running(process_name):
 """ Check if a process with the given name is running. Args: (str):
 Process name, e.g. "Sublime Text" Returns: (bool):
 True if the process is running """

    is_running = False

    # On systems with pgrep, check if the given process is running
    if os.path.isfile('/usr/bin/pgrep'):
        dev_null = open(os.devnull, 'wb')
        returncode = subprocess.call(['/usr/bin/pgrep', process_name],
                                     stdout=dev_null)
        is_running = bool(returncode == 0)

    return is_running