#488 Golang compress

2021-03-01
  • archive: 打包 (tar, zip)
    参考:《Golang archive
  • compress: 压缩 (bzip2, flate, gzip, lzw, zlib)

压缩 & 解压缩

import (
    "bytes"
    "compress/gzip"
    "io"
)

func compressData(data string) ([]byte, error) {
    var buf bytes.Buffer
    gz := gzip.NewWriter(&buf)
    _, err := gz.Write([]byte(data))
    if err != nil {
        return nil, err
    }
    if err := gz.Close(); err != nil {
        return nil, err
    }
    return buf.Bytes(), nil
}

func decompressData(compressedData []byte) (string, error) {
    r, err := gzip.NewReader(bytes.NewReader(compressedData))
    if err != nil {
        return "", err
    }
    defer r.Close()
    decompressedData, err := io.ReadAll(r)
    if err != nil {
        return "", err
    }
    return string(decompressedData), nil
}

压缩 & 解压缩 & 列出压缩包中的内容

import (
    "archive/zip"
)

// 压缩文件
func compressFile(zipFilename string, filenames ...string) error {
    zipFile, err := os.Create(zipFilename)
    if err != nil {
        return err
    }
    defer zipFile.Close()

    zipWriter := zip.NewWriter(zipFile)
    defer zipWriter.Close()

    for _, filename := range filenames {
        file, err := os.Open(filename)
        if err != nil {
            return err
        }
        defer file.Close()
        fi, err := file.Stat()
        if err != nil {
            return err
        }
        fileHeader, err := zip.FileInfoHeader(fi)
        if err != nil {
            return err
        }

        // 设置文件名(压缩后的文件名)
        fileHeader.Name = filename

        // 写入文件头部
        writer, err := zipWriter.CreateHeader(fileHeader)
        if err != nil {
            return err
        }

        // 复制文件内容到压缩包中
        _, err = io.Copy(writer, file)
        if err != nil {
            return err
        }
    }

    return nil
}

// 解压缩文件
func decompressFile(zipFilename, targetDir string) error {
    zipReader, err := zip.OpenReader(zipFilename)
    if err != nil {
        return err
    }
    defer zipReader.Close()

    for _, file := range zipReader.File {
        // 打开压缩包中的文件
        fileReader, err := file.Open()
        if err != nil {
            return err
        }
        defer fileReader.Close()

        // 创建目标文件
        extractedFilePath := fmt.Sprintf("%s/%s", targetDir, file.Name)
        extractedFile, err := os.Create(extractedFilePath)
        if err != nil {
            return err
        }
        defer extractedFile.Close()

        // 复制文件内容到目标文件
        _, err = io.Copy(extractedFile, fileReader)
        if err != nil {
            return err
        }
    }

    return nil
}

func listFilesInZip(zipFilename string) ([]string, error) {
    files := []string{}

    zipReader, err := zip.OpenReader(zipFilename)
    if err != nil {
        return files, err
    }
    defer zipReader.Close()

    for _, file := range zipReader.File {
        files = append(files, file.Name)
    }
    return files, nil
}

#487 Golang archive

2021-03-01

标准库中的 archive 支持 tarzip 两种打包格式。

https://en.wikipedia.org/wiki/Tar_(computing)

最常用的 tar 包:

func createTarArchive(sourceDir, targetFile string) error {
    file, err := os.Create(targetFile)
    if err != nil {
        return err
    }
    defer file.Close()

    tarWriter := tar.NewWriter(file)
    defer tarWriter.Close()

    return filepath.Walk(sourceDir, func(path string, info os.FileInfo, err error) error {
        if err != nil {
            return err
        }

        header, err := tar.FileInfoHeader(info, info.Name())
        if err != nil {
            return err
        }

        if err := tarWriter.WriteHeader(header); err != nil {
            return err
        }

        if !info.IsDir() {
            file, err := os.Open(path)
            if err != nil {
                return err
            }
            defer file.Close()

            _, err = io.Copy(tarWriter, file)
            if err != nil {
                return err
            }
        }

        return nil
    })
}

func extractTarArchive(sourceFile, targetDir string) error {
    file, err := os.Open(sourceFile)
    if err != nil {
        return err
    }
    defer file.Close()

    tarReader := tar.NewReader(file)
    for {
        header, err := tarReader.Next()
        if err == io.EOF {
            break
        }
        if err != nil {
            return err
        }
        targetPath := filepath.Join(targetDir, header.Name)
        if err := os.MkdirAll(filepath.Dir(targetPath), 0755); err != nil {
            return err
        }
        if header.Typeflag == tar.TypeReg {
            file, err := os.Create(targetPath)
            if err != nil {
                return err
            }
            defer file.Close()
            _, err = io.Copy(file, tarReader)
            if err != nil {
                return err
            }
        }
    }

    return nil
}

#486 Golang 数组 & 切片

2021-02-24

数组声明时可以使用 ... 当作长度,表示自动判断。
数组声明时,可以只初始化其中的部分值。

a := [...]int{2: 1, 4: 2} // [5]int{0, 0, 1, 0, 4}

b := [5]int{1, 2, 3} // [5]int{1, 2, 3, 0, 0}

基本操作

a := [...]int{1, 2, 3}
var b []int

// 新增
b = append(b, 1)
// 删除元素
s = append(s[:index], s[index+1:]...)

// 遍历
for i := range a {
    fmt.Println(a[i])
}
for index, value := range a {
    fmt.Printf("%v: %v", index, value)
}
for _, value := range a {
    fmt.Printf("%v", value)
}
for i := 0; i < len(array); i++ {
    fmt.Printf("value: %d\n", array[i])
}

// 判断元素是否存在/获取元素序号
func Index(target int, array []int) int {
    for i, v := range array {
        if target == v {
            return i
        }
    }
    return -1
}

示例

package main

import (
    "fmt"
    "reflect"
)

func main() {
    a := [5]int{1, 3, 5, 7, 9}
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(a), a)
    // [5]int   [5]int{1, 3, 5, 7, 9}

    // array => slice
    b := a[:] // a[0:len(a)]
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(b), b)
    // []int    []int{1, 3, 5, 7, 9}

    // slice => array
    // c := ([5]int)(b) // cannot convert b (type []int) to type [5]int
    c := (*[5]int)(b) // 切片只能转换成数组指针
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(c), c)
    // *[5]int  &[5]int{1, 3, 5, 7, 9}

    // 用类型别名试试:
    type NumArr [5]int
    c2 := (*NumArr)(b)
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(c2), c2)
    // *main.NumArr &main.NumArr{1, 3, 5, 7, 9}

    // 只能遍历赋值
    d := [5]int{}
    for index, v := range b {
        d[index] = v
    }
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(d), d)

    // 通过 copy 的方法实现 slice2array
    e := [5]int{}
    copy(e[:], b) // return length of b
    fmt.Printf("%s\t%#v\n", reflect.TypeOf(e), e)
}

去重

func Unique(arr []int) []int {
    arrLen := len(arr) - 1

    for arrLen > 0 {
        for i := arrLen - 1; i >= 0; i-- {
            if arr[arrLen] == arr[i] {
                arr = append(arr[:i], arr[i+1:]...)
                break
            }
        }
        arrLen--
    }

    return arr
}

func UniqueOptimized(arr []int) []int {
    uniqueArr := make([]int, 0, len(arr))
    uniqueMap := make(map[int]struct{})

    for _, num := range arr {
        if _, ok := uniqueMap[num]; !ok {
            uniqueArr = append(uniqueArr, num)
            uniqueMap[num] = struct{}{}
        }
    }

    return uniqueArr
}

// BenchmarkUniqueOriginal-20           135           8658964 ns/op               0 B/op          0 allocs/op
// BenchmarkUniqueOptimized-20         3501            347027 ns/op          285402 B/op        208 allocs/op

可以看到,一个性能好一些(只用 4% 的时间),资源使用多一些。

使用反射

https://blog.csdn.net/youngwhz1/article/details/83026263

func SliceRemoveDuplicate(a interface{}) (ret []interface{}) {
    if reflect.TypeOf(a).Kind() != reflect.Slice {
        fmt.Printf("<SliceRemoveDuplicate> <a> is not slice but %T\n", a)
        return ret
    }
    va := reflect.ValueOf(a)
    for i := 0; i < va.Len(); i++ {
        if i > 0 && reflect.DeepEqual(va.Index(i-1).Interface(), va.Index(i).Interface()) {
            continue
        }
        ret = append(ret, va.Index(i).Interface())
    }
    return ret
}

func SliceInsert(s []interface{}, index int, value interface{}) []interface{} {
    rear := append([]interface{}{}, s[index:]...)
    return append(append(s[:index], value), rear...)
}

func SliceInsert2(s *[]interface{}, index int, value interface{}) {
    rear := append([]interface{}{}, (*s)[index:]...)
    *s = append(append((*s)[:index], value), rear...)
}

func SliceInsert3(s interface{}, index int, value interface{}) bool {
    if ps, ok := s.(*[]string); ok {
        if val, ok := value.(string); ok {
            rear := append([]string{}, (*ps)[index:]...)
            *ps = append(append((*ps)[:index], val), rear...)
            return true
        }
    } else if ps, ok := s.(*[]int); ok {
        if val, ok := value.(int); ok {
            rear := append([]int{}, (*ps)[index:]...)
            *ps = append(append((*ps)[:index], val), rear...)
        }
    } else if ps, ok := s.(*[]float64); ok {
        if val, ok := value.(float64); ok {
            rear := append([]float64{}, (*ps)[index:]...)
            *ps = append(append((*ps)[:index], val), rear...)
        }
    } else {
        fmt.Printf("<SliceInsert3> Unsupported type: %T\n", s)
    }
    return false
}

func SliceRemove(s []interface{}, index int) []interface{} {
    return append(s[:index], s[index+1:]...)
}

func SliceRemove2(s *[]interface{}, index int) {
    *s = append((*s)[:index], (*s)[index+1:]...)
}

func SliceRemove3(s interface{}, index int) bool {
    if ps, ok := s.(*[]string); ok {
        *ps = append((*ps)[:index], (*ps)[index+1:]...)
    } else if ps, ok := s.(*[]int); ok {
        *ps = append((*ps)[:index], (*ps)[index+1:]...)
    } else if ps, ok := s.(*[]float64); ok {
        *ps = append((*ps)[:index], (*ps)[index+1:]...)
    } else {
        fmt.Printf("<SliceRemove3> Unsupported type: %T\n", s)
        return false
    }
    return true
}

func SliceClear(s *[]interface{}) {
    *s = append([]interface{}{})
}

func SliceClear2(s *[]interface{}) {
    *s = (*s)[0:0]
}

func SliceClear3(s interface{}) bool {
    if ps, ok := s.(*[]string); ok {
        *ps = (*ps)[0:0]
        //*ps = append([]string{})
    } else if ps, ok := s.(*[]int); ok {
        *ps = (*ps)[0:0]
        //*ps = append([]int{})
    } else if ps, ok := s.(*[]float64); ok {
        *ps = (*ps)[0:0]
        //*ps = append([]float64{})
    } else {
        fmt.Printf("<SliceClear3> Unsupported type: %T\n", s)
        return false
    }
    return true
}

泛型实现

func Insert[S ~[]E, E any](s S, i int, v ...E) S {
    tot := len(s) + len(v)
    if tot <= cap(s) {
        s2 := s[:tot]
        copy(s2[i+len(v):], s[i:])
        copy(s2[i:], v)
        return s2
    }
    s2 := make(S, tot)
    copy(s2, s[:i])
    copy(s2[i:], v)
    copy(s2[i+len(v):], s[i:])
    return s2
}

内置方法 make

make(Type, Len, Cap) 可以用来为 slice, map, channel 三种类型初始化(类似:C 语言 (int *)malloc(5))。

这里就看 Slice 的情况。

s1 := make([]int, 5)

s2 := make([]int, 5, 10)
// s2[8] = 1 // panic: runtime error: index out of range [8] with length 5
s2 = append(s2, 1)

如果有预留空间,append 的时候可以不用重新分配内存并遍历赋值。
如果切片有扩容的需要,就最好采用 make 来初始化。

如果不指定容量,则切片的容量和长度将相等。

#485 Golang: 临时文件

2021-02-22
  1. 创建临时文件
  2. 使用编辑器编辑
  3. 获取内容
  4. 删除临时文件
package main

import (
    "bufio"
    "fmt"
    "io/ioutil"
    "log"
    "os"
    "os/exec"
)

func main() {
    // create a tmp file
    // ioutil.TempFile creates a temp file and opens the file for reading and writing
    // and returns the resulting *os.File (file descriptor).
    tmpFile, err := ioutil.TempFile(os.TempDir(), "todo-tmp-")
    if err != nil {
        log.Fatal("Cannot create temporary file", err)
    }
    // defer os.Remove(tmpFile.Name())
    defer tmpFile.Close()
    fmt.Println("Created File: " + tmpFile.Name())

    // choose editor by env var
    editor := os.Getenv("EDITOR")
    args := []string{}
    if editor == "" {
        editor = "vim"
        args = append(args, "--clean")
        fmt.Println("No EDITOR enviroment variable set, use " + editor)
    } else {
        fmt.Println("Using EDITOR enviroment variable: " + editor)
    }
    args = append(args, tmpFile.Name())
    fmt.Println("Opening file with " + editor + " with args: " + fmt.Sprint(args))

    // check the editor command is available
    // _, err = exec.LookPath(editor)
    // if err != nil {
    //  log.Fatal("Cannot find editor: " + editor)
    // }

    // call the editor
    cmd := exec.Command(editor, args...)
    cmd.Stdin = os.Stdin
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr
    err = cmd.Run()
    if err != nil {
        log.Fatal("Cannot run editor: " + editor)
    }

    // read the file
    // data, err := ioutil.ReadFile(tmpFile.Name())
    // if err != nil {
    //  log.Fatal("Cannot read file: " + tmpFile.Name())
    // }
    tmpFile.Seek(0, 0)
    s := bufio.NewScanner(tmpFile)
    for s.Scan() {
        fmt.Println("Content:\n\n" + s.Text())
    }
    if err = s.Err(); err != nil {
        log.Fatal("error reading temp file", err)
    }
}

#484 Golang strings

2021-02-21
func Clone(s string) string                 //
func Compare(a, b string) int               // 比较
func Contains(s, substr string) bool        // 包含子字符串
func ContainsAny(s, chars string) bool      // 包含任意Char
func ContainsRune(s string, r rune) bool    // 包含Rune
func Count(s, substr string) int            // 计数
func Cut(s, sep string) (before, after string, found bool)
func EqualFold(s, t string) bool                    //
func Fields(s string) []string                      // 切割
func FieldsFunc(s string, f func(rune) bool) []string
func HasPrefix(s, prefix string) bool               // 前缀判断 startswith
func HasSuffix(s, suffix string) bool               // 后缀判断 endswith
func Index(s, substr string) int                    // 查找
func IndexAny(s, chars string) int                  // 查找Any
func IndexByte(s string, c byte) int                // 查找Byte
func IndexFunc(s string, f func(rune) bool) int     // 查找Func
func IndexRune(s string, r rune) int                // 查找Rune
func Join(elems []string, sep string) string        // 连接
func LastIndex(s, substr string) int                // 右查找
func LastIndexAny(s, chars string) int              // 右查找Any
func LastIndexByte(s string, c byte) int            // 右查找Byte
func LastIndexFunc(s string, f func(rune) bool) int // 右查找Func
func Map(mapping func(rune) rune, s string) string  //
func Repeat(s string, count int) string             // 重复
func Replace(s, old, new string, n int) string      // 替换
func ReplaceAll(s, old, new string) string          // 替换 = Replace -1
func Split(s, sep string) []string                  // 切割
func SplitAfter(s, sep string) []string             //
func SplitAfterN(s, sep string, n int) []string     //
func SplitN(s, sep string, n int) []string          //
func Title(s string) string                         //
func ToLower(s string) string                       // 转小写
func ToLowerSpecial(c unicode.SpecialCase, s string) string
func ToTitle(s string) string                       // Title
func ToTitleSpecial(c unicode.SpecialCase, s string) string
func ToUpper(s string) string
func ToUpperSpecial(c unicode.SpecialCase, s string) string
func ToValidUTF8(s, replacement string) string
func Trim(s, cutset string) string
func TrimFunc(s string, f func(rune) bool) string
func TrimLeft(s, cutset string) string
func TrimLeftFunc(s string, f func(rune) bool) string
func TrimPrefix(s, prefix string) string
func TrimRight(s, cutset string) string
func TrimRightFunc(s string, f func(rune) bool) string
func TrimSpace(s string) string
func TrimSuffix(s, suffix string) string

type Builder
    func (b *Builder) Cap() int
    func (b *Builder) Grow(n int)
    func (b *Builder) Len() int
    func (b *Builder) Reset()
    func (b *Builder) String() string
    func (b *Builder) Write(p []byte) (int, error)
    func (b *Builder) WriteByte(c byte) error
    func (b *Builder) WriteRune(r rune) (int, error)
    func (b *Builder) WriteString(s string) (int, error)

type Reader
    func NewReader(s string) *Reader
    func (r *Reader) Len() int
    func (r *Reader) Read(b []byte) (n int, err error)
    func (r *Reader) ReadAt(b []byte, off int64) (n int, err error)
    func (r *Reader) ReadByte() (byte, error)
    func (r *Reader) ReadRune() (ch rune, size int, err error)
    func (r *Reader) Reset(s string)
    func (r *Reader) Seek(offset int64, whence int) (int64, error)
    func (r *Reader) Size() int64
    func (r *Reader) UnreadByte() error
    func (r *Reader) UnreadRune() error
    func (r *Reader) WriteTo(w io.Writer) (n int64, err error)

type Replacer
    func NewReplacer(oldnew ...string) *Replacer
    func (r *Replacer) Replace(s string) string
    func (r *Replacer) WriteString(w io.Writer, s string) (n int, err error)

Builder

Reader

Replacer

参考资料与拓展阅读

#483 Python 弱引用

2021-02-20

垃圾回收

Garbage Collector, 简写: GC

Python 垃圾回收是简单基于引用计数

弱引用

在计算机程序设计中,弱引用与强引用相对,是指不能确保其引用的对象不会被垃圾回收器回收的引用。一个对象若只被弱引用所引用,则被认为是不可访问(或弱可访问)的,并因此可能在任何时刻被回收。一些配有垃圾回收机制的语言,如Java、C#、Python、Perl、Lisp等都在不同程度上支持弱引用。

一句话:弱引用不增加计数,对引用计数型 GC 友好一些

垃圾回收与循环引用的问题

import gc

IDS = {}

class A:
    def __del__(self):
        _id = id(self)
        print('A.__del__ %s: 0x%x' % (IDS[_id], _id))

OBJS = {i: A() for i in range(3)}
for i, obj in OBJS.items():
    _id = id(obj)
    IDS[_id] = f'OBJS[{i}]'
    print('%s: 0x%x' % (IDS[_id], _id))
OBJS[1].attr = OBJS[1]
print('1' * 50)
print('====> del OBJS[0]')
del OBJS[0]
print('2' * 50)
print('====> del OBJS[1]')
del OBJS[1]
print('3' * 50)
print('====> del OBJS[2]')
del OBJS[2]
print('4' * 50)
gc.collect()
import weakref

print()
print('=' * 50)
class B:
    def __init__(self, obj):
        self.attrs = [obj]
    def __del__(self):
        _id = id(self)
        print('B.__del__ %s: 0x%x' % (IDS[_id], _id))
a = A()
b = B(a)
a.xyz = b
IDS[id(a)] = 'a'
IDS[id(b)] = 'b'
del a, b  # do nothing
print('=' * 40)
gc.collect()  # will del a and b

print()
print('=' * 50)
class C:
    def __init__(self, obj):
        self.attrs = [weakref.ref(obj)]
    def __del__(self):
        _id = id(self)
        print('C.__del__ %s: 0x%x' % (IDS[_id], _id))
a = A()
c = C(a)
a.xyz = c
IDS[id(a)] = 'a'
IDS[id(c)] = 'c'
del a, c
print('=' * 40)
gc.collect()

标准库:weakref

  • class weakref.ref(object[, callback]) 回调
  • weakref.proxy(object[, callback])
  • weakref.getweakrefcount(object)
  • weakref.getweakrefs(object)
  • class weakref.WeakKeyDictionary([dict])
  • .keyrefs()
  • class weakref.WeakValueDictionary([dict])
  • .valuerefs()
  • class weakref.WeakSet([elements])

    Set class that keeps weak references to its elements. An element will be discarded when no strong reference to it exists any more.

  • class weakref.WeakMethod(method)
  • class weakref.finalize(obj, func, /, *args, **kwargs)
  • weakref.ReferenceType
  • weakref.ProxyType
  • weakref.CallableProxyType
  • weakref.ProxyTypes
import weakref

class Klass:
    pass

obj = Klass()
ref = weakref.ref(obj)
print(ref())
del obj
print(ref())  # None

obj = Klass()
p = weakref.proxy(obj)
print(p)
del obj
print(p)  # ReferenceError: weakly-referenced object no longer exists

参考资料与拓展阅读

#481 Golang reflect

2021-02-17
func Copy(dst, src Value) int
func DeepEqual(x, y any) bool
func Swapper(slice any) func(i, j int)
type ChanDir
    func (d ChanDir) String() string
type Kind
    func (k Kind) String() string
type MapIter
    func (iter *MapIter) Key() Value
    func (iter *MapIter) Next() bool
    func (iter *MapIter) Reset(v Value)
    func (iter *MapIter) Value() Value
type Method
    func (m Method) IsExported() bool
type SelectCase
type SelectDir
type SliceHeader
type StringHeader
type StructField
    func VisibleFields(t Type) []StructField
    func (f StructField) IsExported() bool
type StructTag
    func (tag StructTag) Get(key string) string
    func (tag StructTag) Lookup(key string) (value string, ok bool)

Type

  • func ArrayOf(length int, elem Type) Type
  • func ChanOf(dir ChanDir, t Type) Type
  • func FuncOf(in, out []Type, variadic bool) Type
  • func MapOf(key, elem Type) Type
  • func PointerTo(t Type) Type
  • func PtrTo(t Type) Type
  • func SliceOf(t Type) Type
  • func StructOf(fields []StructField) Type
  • func TypeOf(i any) Type

Value

  • func Append(s Value, x ...Value) Value
  • func AppendSlice(s, t Value) Value
  • func Indirect(v Value) Value
  • func MakeChan(typ Type, buffer int) Value
  • func MakeFunc(typ Type, fn func(args []Value) (results []Value)) Value
  • func MakeMap(typ Type) Value
  • func MakeMapWithSize(typ Type, n int) Value
  • func MakeSlice(typ Type, len, cap int) Value
  • func New(typ Type) Value
  • func NewAt(typ Type, p unsafe.Pointer) Value
  • func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool)
  • func ValueOf(i any) Value
  • func Zero(typ Type) Value
  • func (v Value) Addr() Value
  • func (v Value) Bool() bool
  • func (v Value) Bytes() []byte
  • func (v Value) Call(in []Value) []Value
  • func (v Value) CallSlice(in []Value) []Value
  • func (v Value) CanAddr() bool
  • func (v Value) CanComplex() bool
  • func (v Value) CanConvert(t Type) bool
  • func (v Value) CanFloat() bool
  • func (v Value) CanInt() bool
  • func (v Value) CanInterface() bool
  • func (v Value) CanSet() bool
  • func (v Value) CanUint() bool
  • func (v Value) Cap() int
  • func (v Value) Close()
  • func (v Value) Comparable() bool
  • func (v Value) Complex() complex128
  • func (v Value) Convert(t Type) Value
  • func (v Value) Elem() Value
  • func (v Value) Equal(u Value) bool
  • func (v Value) Field(i int) Value
  • func (v Value) FieldByIndex(index []int) Value
  • func (v Value) FieldByIndexErr(index []int) (Value, error)
  • func (v Value) FieldByName(name string) Value
  • func (v Value) FieldByNameFunc(match func(string) bool) Value
  • func (v Value) Float() float64
  • func (v Value) Grow(n int)
  • func (v Value) Index(i int) Value
  • func (v Value) Int() int64
  • func (v Value) Interface() (i any)
  • func (v Value) InterfaceData() [2]uintptrDEPRECATED
  • func (v Value) IsNil() bool
  • func (v Value) IsValid() bool
  • func (v Value) IsZero() bool
  • func (v Value) Kind() Kind
  • func (v Value) Len() int
  • func (v Value) MapIndex(key Value) Value
  • func (v Value) MapKeys() []Value
  • func (v Value) MapRange() *MapIter
  • func (v Value) Method(i int) Value
  • func (v Value) MethodByName(name string) Value
  • func (v Value) NumField() int
  • func (v Value) NumMethod() int
  • func (v Value) OverflowComplex(x complex128) bool
  • func (v Value) OverflowFloat(x float64) bool
  • func (v Value) OverflowInt(x int64) bool
  • func (v Value) OverflowUint(x uint64) bool
  • func (v Value) Pointer() uintptr
  • func (v Value) Recv() (x Value, ok bool)
  • func (v Value) Send(x Value)
  • func (v Value) Set(x Value)
  • func (v Value) SetBool(x bool)
  • func (v Value) SetBytes(x []byte)
  • func (v Value) SetCap(n int)
  • func (v Value) SetComplex(x complex128)
  • func (v Value) SetFloat(x float64)
  • func (v Value) SetInt(x int64)
  • func (v Value) SetIterKey(iter *MapIter)
  • func (v Value) SetIterValue(iter *MapIter)
  • func (v Value) SetLen(n int)
  • func (v Value) SetMapIndex(key, elem Value)
  • func (v Value) SetPointer(x unsafe.Pointer)
  • func (v Value) SetString(x string)
  • func (v Value) SetUint(x uint64)
  • func (v Value) SetZero()
  • func (v Value) Slice(i, j int) Value
  • func (v Value) Slice3(i, j, k int) Value
  • func (v Value) String() string
  • func (v Value) TryRecv() (x Value, ok bool)
  • func (v Value) TrySend(x Value) bool
  • func (v Value) Type() Type
  • func (v Value) Uint() uint64
  • func (v Value) UnsafeAddr() uintptr
  • func (v Value) UnsafePointer() unsafe.Pointer

#480 修改 cmd 字体

2021-02-14

Windows CMD 太挫,中文字体选择少,XP, Win7 下只有点阵字体 (fixedsys) 和新宋体,Win10 字体又多了几个,但效果页不太好。
不过 Win10 的话,可能是半年前吧,微软新出来了一个 Windows Terminal 的虚拟终端,就现代化多了。现在我在 Windows 下(偶尔)一般都是用的新版 Terminal + PowerShell,听方便。
但如果由于 OS 版本等问题,离不开 cmd 的话,有两个方法,一个是使用第三方终端模拟器,比如 cmder;再一个就是想办法定制一下 cmd 的字体。
我在这里记录一下之前使用的一个方案失效地址(确认有效,不过好久都没有用了)。

#479 Golang io

2021-02-14

io, io/fs, io/util, os

find /usr/share/go-1.17/src/io/ -type f | grep -Fv _test.go
/usr/share/go-1.17/src/io/ioutil/testdata/hello
/usr/share/go-1.17/src/io/ioutil/tempfile.go
/usr/share/go-1.17/src/io/ioutil/ioutil.go
/usr/share/go-1.17/src/io/pipe.go
/usr/share/go-1.17/src/io/fs/fs.go
/usr/share/go-1.17/src/io/fs/readfile.go
/usr/share/go-1.17/src/io/fs/readdir.go
/usr/share/go-1.17/src/io/fs/sub.go
/usr/share/go-1.17/src/io/fs/stat.go
/usr/share/go-1.17/src/io/fs/walk.go
/usr/share/go-1.17/src/io/fs/glob.go
/usr/share/go-1.17/src/io/io.go
/usr/share/go-1.17/src/io/multi.go

方法

https://pkg.go.dev/io

相关方法

io.Reader / io.Writer

type Reader interface {
    Read(p []byte) (n int, err error)
}

type Writer interface {
    Write(p []byte) (n int, err error)
}

stringsbytesbufioos.File 都是 io.Reader 的实现。

小技巧:利用类型断言检查是否实现指定接口

https://stackoverflow.com/a/25677274

var _ io.Reader = (*os.File)(nil)
// nil 可以转换成任意类型的空指针
// 这里将 nil 转换成 os.File 指针,再赋值给 io.Reader 类型

io/fs

func Glob(fsys FS, pattern string) (matches []string, err error)
func ReadFile(fsys FS, name string) ([]byte, error)
func ValidPath(name string) bool
func WalkDir(fsys FS, root string, fn WalkDirFunc) error

io/util 包 (原 ioutil)

1.6 以及之后新版本,iouitl 包依然保留,但是只是对 io 包的封装。

Package ioutil implements some I/O utility functions.
As of Go 1.16, the same functionality is now provided by package io or package os, and those implementations should be preferred in new code. See the specific function documentation for details.

  1. func NopCloser(r io.Reader) io.ReadCloser
  2. func ReadAll(r io.Reader) ([]byte, error)
  3. func ReadDir(dirname string) ([]fs.FileInfo, error)
  4. func ReadFile(filename string) ([]byte, error)
  5. func TempDir(dir, pattern string) (name string, err error)
  6. func TempFile(dir, pattern string) (f *os.File, err error)
  7. func WriteFile(filename string, data []byte, perm fs.FileMode) error
// grep -REv "^//" /usr/share/go-1.17/src/io/ioutil/tempfile.go
package ioutil

import (
        "os"
)

func TempFile(dir, pattern string) (f *os.File, err error) {
        return os.CreateTemp(dir, pattern)
}

func TempDir(dir, pattern string) (name string, err error) {
        return os.MkdirTemp(dir, pattern)
}
// grep -REv "^//" /usr/share/go-1.17/src/io/ioutil/ioutil.go
package ioutil

import (
        "io"
        "io/fs"
        "os"
        "sort"
)

func ReadAll(r io.Reader) ([]byte, error) {
        return io.ReadAll(r)
}

func ReadFile(filename string) ([]byte, error) {
        return os.ReadFile(filename)
}

func WriteFile(filename string, data []byte, perm fs.FileMode) error {
        return os.WriteFile(filename, data, perm)
}

func ReadDir(dirname string) ([]fs.FileInfo, error) {
        f, err := os.Open(dirname)
        if err != nil {
                return nil, err
        }
        list, err := f.Readdir(-1)
        f.Close()
        if err != nil {
                return nil, err
        }
        sort.Slice(list, func(i, j int) bool { return list[i].Name() < list[j].Name() })
        return list, nil
}

func NopCloser(r io.Reader) io.ReadCloser {
        return io.NopCloser(r)
}

var Discard io.Writer = io.Discard

引申

io 包是基础,提供了 Reader 和 Writer 接口。其他包则是实现这两个接口。

string 包:字符串 IO

相当于 Python io.StringIO

  • string.Reader

bytes 包:字节 IO

通过 []byte 模拟 io,相当于 Python io.BytesIO

  • bytes.Buffer (Reader + Writer)
  • bytes.Reader

buffio 包:缓冲 IO

就是加入了一个缓冲的功能,提升 IO 效率,减少直接系统调用。
也方便实现一些网络协议中的分包,比如 SMTP 协议中按换行切割。

  • bufio.Reader
  • bufio.Writer
package main

import (
    "bufio"
    "fmt"
    "os"
)

func main() {
    file, err := os.Open("test.txt")
    if err != nil {
        fmt.Println("无法打开文件:", err)
        return
    }
    defer file.Close()

    reader := bufio.NewReader(file)
    for {
        line, err := reader.ReadString('\n')
        if err != nil {
            // 文件结束或发生错误
            break
        }
        fmt.Print(line)
    }
}

os 包:系统 IO

  • os.File 文件类型
func Open(name string) (*File, error)
func OpenFile(name string, flag int, perm FileMode) (*File, error)

var Stdin = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
var Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
var Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")

net 包:网络 IO

网络编程的部分,这里就不继续展开了。

  • net.Conn 网络连接
func Pipe() (Conn, Conn)

func Dial(network, address string) (Conn, error)
func DialTimeout(network, address string, timeout time.Duration) (Conn, error)
func FileConn(f *os.File) (c Conn, err error)

func (d *Dialer) Dial(network, address string) (Conn, error)
func (d *Dialer) DialContext(ctx context.Context, network, address string) (Conn, error)

func FilePacketConn(f *os.File) (c PacketConn, err error)
func ListenPacket(network, address string) (PacketConn, error)

func DialIP(network string, laddr, raddr *IPAddr) (*IPConn, error)
func ListenIP(network string, laddr *IPAddr) (*IPConn, error)

func DialTCP(network string, laddr, raddr *TCPAddr) (*TCPConn, error)
func (l *TCPListener) Accept() (Conn, error)
func (l *TCPListener) AcceptTCP() (*TCPConn, error)

func DialUDP(network string, laddr, raddr *UDPAddr) (*UDPConn, error)
func ListenMulticastUDP(network string, ifi *Interface, gaddr *UDPAddr) (*UDPConn, error)
func ListenUDP(network string, laddr *UDPAddr) (*UDPConn, error)

func DialUnix(network string, laddr, raddr *UnixAddr) (*UnixConn, error)
func ListenUnixgram(network string, laddr *UnixAddr) (*UnixConn, error)
func (l *UnixListener) Accept() (Conn, error)
func (l *UnixListener) AcceptUnix() (*UnixConn, error)