def gettz()

in lib/dateutil/tz/tz.py [0:0]
69 lines of code
27 McCabe index (conditional complexity)

def gettz(name=None):
    tz = None
    if not name:
        try:
            name = os.environ["TZ"]
        except KeyError:
            pass
    if name is None or name == ":":
        for filepath in TZFILES:
            if not os.path.isabs(filepath):
                filename = filepath
                for path in TZPATHS:
                    filepath = os.path.join(path, filename)
                    if os.path.isfile(filepath):
                        break
                else:
                    continue
            if os.path.isfile(filepath):
                try:
                    tz = tzfile(filepath)
                    break
                except (IOError, OSError, ValueError):
                    pass
        else:
            tz = tzlocal()
    else:
        if name.startswith(":"):
            name = name[:-1]
        if os.path.isabs(name):
            if os.path.isfile(name):
                tz = tzfile(name)
            else:
                tz = None
        else:
            for path in TZPATHS:
                filepath = os.path.join(path, name)
                if not os.path.isfile(filepath):
                    filepath = filepath.replace(' ', '_')
                    if not os.path.isfile(filepath):
                        continue
                try:
                    tz = tzfile(filepath)
                    break
                except (IOError, OSError, ValueError):
                    pass
            else:
                tz = None
                if tzwin is not None:
                    try:
                        tz = tzwin(name)
                    except WindowsError:
                        tz = None

                if not tz:
                    from dateutil.zoneinfo import get_zonefile_instance
                    tz = get_zonefile_instance().get(name)

                if not tz:
                    for c in name:
                        # name must have at least one offset to be a tzstr
                        if c in "0123456789":
                            try:
                                tz = tzstr(name)
                            except ValueError:
                                pass
                            break
                    else:
                        if name in ("GMT", "UTC"):
                            tz = tzutc()
                        elif name in time.tzname:
                            tz = tzlocal()
    return tz