<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _where(filename, dirs=[], env="PATH"):
 """Find file in current dir or system path"""

    if not isinstance(dirs, list):
        dirs = [dirs]
    if glob(filename):
        return filename
    paths = [os.curdir] + os.environ[env].split(os.path.pathsep) + dirs
    for path in paths:
        for match in glob(os.path.join(path, filename)):
            if match:
                return os.path.normpath(match)
    raise IOError("File not found: %s" % filename)