def METHOD_NAME(command, paths = None):
    """which(command, [paths]) - Look up the given command in the paths string
    (or the PATH environment variable, if unspecified)."""
    if paths is None:
        paths = os.environ.get('PATH','')
    # Check for absolute match first.
    if os.path.isfile(command):
        return command
    # Would be nice if Python had a lib function for this.
    if not paths:
        paths = os.defpath
    # Get suffixes to search.
    # On Cygwin, 'PATHEXT' may exist but it should not be used.
    if os.pathsep == ';':
        pathext = os.environ.get('PATHEXT', '').split(';')
    else:
        pathext = ['']
    # Search the paths...
    for path in paths.split(os.pathsep):
        for ext in pathext:
            p = os.path.join(path, command + ext)
            if os.path.exists(p):
                return p
    return None