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