func SelectorFromSet(ls Set) Selector {
	if ls == nil {
		return internalSelector{}
	}
	var requirements internalSelector
	for label, value := range ls {
		if r, err := NewRequirement(label, selection.Equals, sets.NewString(value)); err != nil {
			return internalSelector{}
		} else {
			requirements = append(requirements, *r)
		}
	}
	sort.Sort(ByKey(requirements))
	return internalSelector(requirements)
}
SelectorFromSet returns a Selector which will match exactly the given Set. A
nil and empty Sets are considered equivalent to Everything().
package labels
import (
	"bytes"
	"fmt"
	"sort"
	"strconv"
	"strings"
	"github.com/golang/glog"
	"k8s.io/kubernetes/pkg/selection"
	"k8s.io/kubernetes/pkg/util/sets"
	"k8s.io/kubernetes/pkg/util/validation"
)
type Requirements []Requirement
type Selector interface {
	Matches(Labels) bool
	Empty() bool
	String() string
	Add(r ...Requirement) Selector
	Requirements() (requirements Requirements, selectable bool)
}
func Everything() Selector {
	return internalSelector{}
}
type nothingSelector struct{}
func (n nothingSelector) Matches(_ Labels) bool              { return false }
func (n nothingSelector) Empty() bool                        { return false }
func (n nothingSelector) String() string                     { return "<null>" }
func (n nothingSelector) Add(_ ...Requirement) Selector      { return n }
func (n nothingSelector) Requirements() (Requirements, bool) { return nil, false }
func Nothing() Selector {
	return nothingSelector{}
}
func NewSelector() Selector {
	return internalSelector(nil)
}
type internalSelector []Requirement
type ByKey []Requirement
func (a ByKey) Len() int { return len(a) }
func (a ByKey) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a ByKey) Less(i, j int) bool { return a[i].key < a[j].key }
type Requirement struct {
	key       string
	operator  selection.Operator
	strValues sets.String
}
func NewRequirement(key string, op selection.Operator, vals sets.String) (*Requirement, error) {
	if err := validateLabelKey(key); err != nil {
		return nil, err
	}
	switch op {
	case selection.In, selection.NotIn:
		if len(vals) == 0 {
			return nil, fmt.Errorf("for 'in', 'notin' operators, values set can't be empty")
		}
	case selection.Equals, selection.DoubleEquals, selection.NotEquals:
		if len(vals) != 1 {
			return nil, fmt.Errorf("exact-match compatibility requires one single value")
		}
	case selection.Exists, selection.DoesNotExist:
		if len(vals) != 0 {
			return nil, fmt.Errorf("values set must be empty for exists and does not exist")
		}
	case selection.GreaterThan, selection.LessThan:
		if len(vals) != 1 {
			return nil, fmt.Errorf("for 'Gt', 'Lt' operators, exactly one value is required")
		}
		for val := range vals {
			if _, err := strconv.ParseInt(val, 10, 64); err != nil {
				return nil, fmt.Errorf("for 'Gt', 'Lt' operators, the value must be an integer")
			}
		}
	default:
		return nil, fmt.Errorf("operator '%v' is not recognized", op)
	}
	for v := range vals {
		if err := validateLabelValue(v); err != nil {
			return nil, err
		}
	}
	return &Requirement{key: key, operator: op, strValues: vals}, nil
}
func (r *Requirement) Matches(ls Labels) bool {
	switch r.operator {
	case selection.In, selection.Equals, selection.DoubleEquals:
		if !ls.Has(r.key) {
			return false
		}
		return r.strValues.Has(ls.Get(r.key))
	case selection.NotIn, selection.NotEquals:
		if !ls.Has(r.key) {
			return true
		}
		return !r.strValues.Has(ls.Get(r.key))
	case selection.Exists:
		return ls.Has(r.key)
	case selection.DoesNotExist:
		return !ls.Has(r.key)
	case selection.GreaterThan, selection.LessThan:
		if !ls.Has(r.key) {
			return false
		}
		lsValue, err := strconv.ParseInt(ls.Get(r.key), 10, 64)
		if err != nil {
			glog.V(10).Infof("ParseInt failed for value %+v in label %+v, %+v", ls.Get(r.key), ls, err)
			return false
		}
		if len(r.strValues) != 1 {
			glog.V(10).Infof("Invalid values count %+v of requirement %#v, for 'Gt', 'Lt' operators, exactly one value is required", len(r.strValues), r)
			return false
		}
		var rValue int64
		for strValue := range r.strValues {
			rValue, err = strconv.ParseInt(strValue, 10, 64)
			if err != nil {
				glog.V(10).Infof("ParseInt failed for value %+v in requirement %#v, for 'Gt', 'Lt' operators, the value must be an integer", strValue, r)
				return false
			}
		}
		return (r.operator == selection.GreaterThan && lsValue > rValue) || (r.operator == selection.LessThan && lsValue < rValue)
	default:
		return false
	}
}
func (r *Requirement) Key() string {
	return r.key
}
func (r *Requirement) Operator() selection.Operator {
	return r.operator
}
func (r *Requirement) Values() sets.String {
	ret := sets.String{}
	for k := range r.strValues {
		ret.Insert(k)
	}
	return ret
}
func (lsel internalSelector) Empty() bool {
	if lsel == nil {
		return true
	}
	return len(lsel) == 0
}
func (r *Requirement) String() string {
	var buffer bytes.Buffer
	if r.operator == selection.DoesNotExist {
		buffer.WriteString("!")
	}
	buffer.WriteString(r.key)
	switch r.operator {
	case selection.Equals:
		buffer.WriteString("=")
	case selection.DoubleEquals:
		buffer.WriteString("==")
	case selection.NotEquals:
		buffer.WriteString("!=")
	case selection.In:
		buffer.WriteString(" in ")
	case selection.NotIn:
		buffer.WriteString(" notin ")
	case selection.GreaterThan:
		buffer.WriteString(">")
	case selection.LessThan:
		buffer.WriteString("<")
	case selection.Exists, selection.DoesNotExist:
		return buffer.String()
	}
	switch r.operator {
	case selection.In, selection.NotIn:
		buffer.WriteString("(")
	}
	if len(r.strValues) == 1 {
		buffer.WriteString(r.strValues.List()[0])
	} else {  
		buffer.WriteString(strings.Join(r.strValues.List(), ","))
	}
	switch r.operator {
	case selection.In, selection.NotIn:
		buffer.WriteString(")")
	}
	return buffer.String()
}
func (lsel internalSelector) Add(reqs ...Requirement) Selector {
	var sel internalSelector
	for ix := range lsel {
		sel = append(sel, lsel[ix])
	}
	for _, r := range reqs {
		sel = append(sel, r)
	}
	sort.Sort(ByKey(sel))
	return sel
}
func (lsel internalSelector) Matches(l Labels) bool {
	for ix := range lsel {
		if matches := lsel[ix].Matches(l); !matches {
			return false
		}
	}
	return true
}
func (lsel internalSelector) Requirements() (Requirements, bool) { return Requirements(lsel), true }
func (lsel internalSelector) String() string {
	var reqs []string
	for ix := range lsel {
		reqs = append(reqs, lsel[ix].String())
	}
	return strings.Join(reqs, ",")
}
type Token int
const (
	ErrorToken Token = iota
	EndOfStringToken
	ClosedParToken
	CommaToken
	DoesNotExistToken
	DoubleEqualsToken
	EqualsToken
	GreaterThanToken
	IdentifierToken  
	InToken
	LessThanToken
	NotEqualsToken
	NotInToken
	OpenParToken
)
var string2token = map[string]Token{
	")":     ClosedParToken,
	",":     CommaToken,
	"!":     DoesNotExistToken,
	"==":    DoubleEqualsToken,
	"=":     EqualsToken,
	">":     GreaterThanToken,
	"in":    InToken,
	"<":     LessThanToken,
	"!=":    NotEqualsToken,
	"notin": NotInToken,
	"(":     OpenParToken,
}
type ScannedItem struct {
	tok     Token
	literal string
}
func isWhitespace(ch byte) bool {
	return ch == ' ' || ch == '\t' || ch == '\r' || ch == '\n'
}
func isSpecialSymbol(ch byte) bool {
	switch ch {
	case '=', '!', '(', ')', ',', '>', '<':
		return true
	}
	return false
}
type Lexer struct {
	s string
	pos int
}
func (l *Lexer) read() (b byte) {
	b = 0
	if l.pos < len(l.s) {
		b = l.s[l.pos]
		l.pos++
	}
	return b
}
func (l *Lexer) unread() {
	l.pos--
}
func (l *Lexer) scanIdOrKeyword() (tok Token, lit string) {
	var buffer []byte
IdentifierLoop:
	for {
		switch ch := l.read(); {
		case ch == 0:
			break IdentifierLoop
		case isSpecialSymbol(ch) || isWhitespace(ch):
			l.unread()
			break IdentifierLoop
		default:
			buffer = append(buffer, ch)
		}
	}
	s := string(buffer)
	if val, ok := string2token[s]; ok {  
		return val, s
	}
	return IdentifierToken, s  
}
func (l *Lexer) scanSpecialSymbol() (Token, string) {
	lastScannedItem := ScannedItem{}
	var buffer []byte
SpecialSymbolLoop:
	for {
		switch ch := l.read(); {
		case ch == 0:
			break SpecialSymbolLoop
		case isSpecialSymbol(ch):
			buffer = append(buffer, ch)
			if token, ok := string2token[string(buffer)]; ok {
				lastScannedItem = ScannedItem{tok: token, literal: string(buffer)}
			} else if lastScannedItem.tok != 0 {
				l.unread()
				break SpecialSymbolLoop
			}
		default:
			l.unread()
			break SpecialSymbolLoop
		}
	}
	if lastScannedItem.tok == 0 {
		return ErrorToken, fmt.Sprintf("error expected: keyword found '%s'", buffer)
	}
	return lastScannedItem.tok, lastScannedItem.literal
}
func (l *Lexer) skipWhiteSpaces(ch byte) byte {
	for {
		if !isWhitespace(ch) {
			return ch
		}
		ch = l.read()
	}
}
func (l *Lexer) Lex() (tok Token, lit string) {
	switch ch := l.skipWhiteSpaces(l.read()); {
	case ch == 0:
		return EndOfStringToken, ""
	case isSpecialSymbol(ch):
		l.unread()
		return l.scanSpecialSymbol()
	default:
		l.unread()
		return l.scanIdOrKeyword()
	}
}
type Parser struct {
	l            *Lexer
	scannedItems []ScannedItem
	position     int
}
type ParserContext int
const (
	KeyAndOperator ParserContext = iota
	Values
)
func (p *Parser) lookahead(context ParserContext) (Token, string) {
	tok, lit := p.scannedItems[p.position].tok, p.scannedItems[p.position].literal
	if context == Values {
		switch tok {
		case InToken, NotInToken:
			tok = IdentifierToken
		}
	}
	return tok, lit
}
func (p *Parser) consume(context ParserContext) (Token, string) {
	p.position++
	tok, lit := p.scannedItems[p.position-1].tok, p.scannedItems[p.position-1].literal
	if context == Values {
		switch tok {
		case InToken, NotInToken:
			tok = IdentifierToken
		}
	}
	return tok, lit
}
func (p *Parser) scan() {
	for {
		token, literal := p.l.Lex()
		p.scannedItems = append(p.scannedItems, ScannedItem{token, literal})
		if token == EndOfStringToken {
			break
		}
	}
}
func (p *Parser) parse() (internalSelector, error) {
	p.scan()  
	var requirements internalSelector
	for {
		tok, lit := p.lookahead(Values)
		switch tok {
		case IdentifierToken, DoesNotExistToken:
			r, err := p.parseRequirement()
			if err != nil {
				return nil, fmt.Errorf("unable to parse requirement: %v", err)
			}
			requirements = append(requirements, *r)
			t, l := p.consume(Values)
			switch t {
			case EndOfStringToken:
				return requirements, nil
			case CommaToken:
				t2, l2 := p.lookahead(Values)
				if t2 != IdentifierToken && t2 != DoesNotExistToken {
					return nil, fmt.Errorf("found '%s', expected: identifier after ','", l2)
				}
			default:
				return nil, fmt.Errorf("found '%s', expected: ',' or 'end of string'", l)
			}
		case EndOfStringToken:
			return requirements, nil
		default:
			return nil, fmt.Errorf("found '%s', expected: !, identifier, or 'end of string'", lit)
		}
	}
}
func (p *Parser) parseRequirement() (*Requirement, error) {
	key, operator, err := p.parseKeyAndInferOperator()
	if err != nil {
		return nil, err
	}
	if operator == selection.Exists || operator == selection.DoesNotExist {  
		return NewRequirement(key, operator, nil)
	}
	operator, err = p.parseOperator()
	if err != nil {
		return nil, err
	}
	var values sets.String
	switch operator {
	case selection.In, selection.NotIn:
		values, err = p.parseValues()
	case selection.Equals, selection.DoubleEquals, selection.NotEquals, selection.GreaterThan, selection.LessThan:
		values, err = p.parseExactValue()
	}
	if err != nil {
		return nil, err
	}
	return NewRequirement(key, operator, values)
}
func (p *Parser) parseKeyAndInferOperator() (string, selection.Operator, error) {
	var operator selection.Operator
	tok, literal := p.consume(Values)
	if tok == DoesNotExistToken {
		operator = selection.DoesNotExist
		tok, literal = p.consume(Values)
	}
	if tok != IdentifierToken {
		err := fmt.Errorf("found '%s', expected: identifier", literal)
		return "", "", err
	}
	if err := validateLabelKey(literal); err != nil {
		return "", "", err
	}
	if t, _ := p.lookahead(Values); t == EndOfStringToken || t == CommaToken {
		if operator != selection.DoesNotExist {
			operator = selection.Exists
		}
	}
	return literal, operator, nil
}
func (p *Parser) parseOperator() (op selection.Operator, err error) {
	tok, lit := p.consume(KeyAndOperator)
	switch tok {
	case InToken:
		op = selection.In
	case EqualsToken:
		op = selection.Equals
	case DoubleEqualsToken:
		op = selection.DoubleEquals
	case GreaterThanToken:
		op = selection.GreaterThan
	case LessThanToken:
		op = selection.LessThan
	case NotInToken:
		op = selection.NotIn
	case NotEqualsToken:
		op = selection.NotEquals
	default:
		return "", fmt.Errorf("found '%s', expected: '=', '!=', '==', 'in', notin'", lit)
	}
	return op, nil
}
func (p *Parser) parseValues() (sets.String, error) {
	tok, lit := p.consume(Values)
	if tok != OpenParToken {
		return nil, fmt.Errorf("found '%s' expected: '('", lit)
	}
	tok, lit = p.lookahead(Values)
	switch tok {
	case IdentifierToken, CommaToken:
		s, err := p.parseIdentifiersList()  
		if err != nil {
			return s, err
		}
		if tok, _ = p.consume(Values); tok != ClosedParToken {
			return nil, fmt.Errorf("found '%s', expected: ')'", lit)
		}
		return s, nil
	case ClosedParToken:  
		p.consume(Values)
		return sets.NewString(""), nil
	default:
		return nil, fmt.Errorf("found '%s', expected: ',', ')' or identifier", lit)
	}
}
func (p *Parser) parseIdentifiersList() (sets.String, error) {
	s := sets.NewString()
	for {
		tok, lit := p.consume(Values)
		switch tok {
		case IdentifierToken:
			s.Insert(lit)
			tok2, lit2 := p.lookahead(Values)
			switch tok2 {
			case CommaToken:
				continue
			case ClosedParToken:
				return s, nil
			default:
				return nil, fmt.Errorf("found '%s', expected: ',' or ')'", lit2)
			}
		case CommaToken:  
			if s.Len() == 0 {
				s.Insert("")  
			}
			tok2, _ := p.lookahead(Values)
			if tok2 == ClosedParToken {
				s.Insert("")  
				return s, nil
			}
			if tok2 == CommaToken {
				p.consume(Values)
				s.Insert("")  
			}
		default:  
			return s, fmt.Errorf("found '%s', expected: ',', or identifier", lit)
		}
	}
}
func (p *Parser) parseExactValue() (sets.String, error) {
	s := sets.NewString()
	tok, lit := p.lookahead(Values)
	if tok == EndOfStringToken || tok == CommaToken {
		s.Insert("")
		return s, nil
	}
	tok, lit = p.consume(Values)
	if tok == IdentifierToken {
		s.Insert(lit)
		return s, nil
	}
	return nil, fmt.Errorf("found '%s', expected: identifier", lit)
}
func Parse(selector string) (Selector, error) {
	parsedSelector, err := parse(selector)
	if err == nil {
		return parsedSelector, nil
	}
	return nil, err
}
func parse(selector string) (internalSelector, error) {
	p := &Parser{l: &Lexer{s: selector, pos: 0}}
	items, err := p.parse()
	if err != nil {
		return nil, err
	}
	sort.Sort(ByKey(items))  
	return internalSelector(items), err
}
func validateLabelKey(k string) error {
	if errs := validation.IsQualifiedName(k); len(errs) != 0 {
		return fmt.Errorf("invalid label key %q: %s", k, strings.Join(errs, "; "))
	}
	return nil
}
func validateLabelValue(v string) error {
	if errs := validation.IsValidLabelValue(v); len(errs) != 0 {
		return fmt.Errorf("invalid label value: %q: %s", v, strings.Join(errs, "; "))
	}
	return nil
}