def check_for(texsystem): #<- different commands are asked for, but not actually checked below...
    header = """
    \\documentclass{minimal}
    \\usepackage{pgf}
    \\begin{document}
    \\typeout{pgfversion=\\pgfversion}
    \\makeatletter
    \\@@end
    """
    try:
        latex = subprocess.Popen(["xelatex", "-halt-on-error"], #<- why not texsystem? 
                                 stdin=subprocess.PIPE,
                                 stdout=subprocess.PIPE)
        stdout, stderr = latex.communicate(header.encode("utf8"))
    except OSError:
        return False

    return latex.returncode == 0