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pyscript用python写JavaScript

在B站@mlln-cn, 我就能回答你的问题奥!

2018年07月13日
文章目录
  1. 1. pyscript简介
  2. 2. 目标
  3. 3. 注意
  4. 4. 案例
    1. 4.1. 基本操作
    2. 4.2. 数据类型
    3. 4.3. 切片操作和取值
    4. 4.4. 格式化字符串
    5. 4.5. 赋值操作
    6. 4.6. 比较
    7. 4.7. Truthy和Falsy
    8. 4.8. 函数操作
    9. 4.9. if语句
    10. 4.10. 循环
    11. 4.11. list 推导
    12. 4.12. 定义函数
    13. 4.13. 定义类
    14. 4.14. 异常
    15. 4.15. python内置函数
    16. 4.16. isinstance相关功能
    17. 4.17. hasattr, getattr, setattr and delattr
    18. 4.18. 使用JS专属功能

声明: 本文由DataScience发表,未经允许不得转载。 转载请注明本文链接mlln.cn, 并在文后留言转载.

本文代码运行环境:

  • windows10
  • jupyter notebook
  • python3.6

pyscript简介

pyscript模块提供了将Python代码转换为JavaScript的功能。这是使用PyScript的简要介绍。有关详细信息，请参阅以下部分。

PyScript是一种使用Python语言编写JavaScript的工具。支持所有相关的内置功能，以及list，dict和str的方法。不支持set，带step参数的切片操作，yield和import。除此之外，大多数Python代码应该按预期工作…根据经验，代码在正确时应该按预期运行，但错误报告可能不是非常Pythonic。

您需要了解的最重要的函数是py2js和evalpy。原则上，您不需要JavaScript的知识来编写PyScript代码，尽管它在极端情况下确实有帮助。

目标

使用web技术实现可视化和用户交互的Python项目有所增加。 PyScript允许用户在Python中编写JavaScript回调，实现交互的灵活/快速。

这导致了以下两个主要目标：

通过让人们使用Python语法和内置函数来编写javascript，并修复一些JavaScripts怪癖，使编写JavaScript变得更容易，更不令人沮丧。允许在Python程序中定义JavaScript代码段。PyScript生成的代码可以独立工作。任何（PyScript兼容的）Python片段都可以转换为JS;你不需要另一个JS库来运行它。

PyScript还可用于开发独立的JavaScript（AMD）模块。

注意

PyScript修复了JS的一些怪癖，但它仍然只是JavaScript。这是一个值得关注的事项列表。此列表可能不完整。如果您打算大量使用PyScript，我们建议您熟悉JavaScript。

  • JavasScript有一个null（即None）的概念，以及undefined。有时您可能想要使用if x is None or x is undefined
  • 访问不存在的属性不会引发AttributeError但会产生undefined, 这是JavaScript的特性
  • 类上的魔术函数（例如，用于运算符重载）不起作用。
  • 调用以大写字母开头的对象被假定为类实例化（使用new）：PyScript类必须以大写字母开头，而任何其他callables都不能。
  • 如果函数具有** kwargs参数或* args之后的命名参数，则函数可以接受它。将关键字传递给不处理关键字参数的函数可能会导致混淆错误。

案例

为了在notebook中实时显示python转JavaScript的过程, 我们注册一个魔法函数, 功能很简单, 就是把python代码转成JavaScript, 并显示在输出区域。

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from IPython.core.magic import register_cell_magic
from IPython.display import Markdown


@register_cell_magic
def py2js(line, cell):
    from pscript import py2js
    js= py2js(cell)
    return Markdown(f'```javascript\n{js}\n```')
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%%py2js

a = 1
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var a;
a = 1;

基本操作

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%%py2js

# Simple operations
3 + 4 -1
3 * 7 / 9
5**2
pow(5, 2)
7 // 2
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var _pyfunc_pow = Math.pow;
(3 + 4) - 1;
(3 * 7) / 9;
Math.pow(5, 2);
_pyfunc_pow(5, 2);
Math.floor(7/2);

数据类型

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%%py2js

[True, False, None]

foo = [1, 2, 3]
bar = {'a': 1, 'b': 2}
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var bar, foo;
[true, false, null];
foo = [1, 2, 3];
bar = ({a: 1, b: 2});
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%%py2js

a = [2,3,4]
a.sort()
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var _pymeth_sort = function (key, reverse) { // nargs: 0 1 2
    if (!Array.isArray(this)) return this.sort.apply(this, arguments);
    var comp = function (a, b) {a = key(a); b = key(b);
        if (a<b) {return -1;} if (a>b) {return 1;} return 0;};
    comp = Boolean(key) ? comp : undefined; 
    this.sort(comp);
    if (reverse) this.reverse();
};
var a;
a = [2, 3, 4];
_pymeth_sort.call(a, undefined, false);

切片操作和取值

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%%py2js

foo = [1, 2, 3, 4, 5]
foo[2:]
foo[2:-2]
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var foo;
foo = [1, 2, 3, 4, 5];
foo.slice(2);
foo.slice(2,-2);
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%%py2js
bar = 'abcdefghij'
bar[2:]
bar[2:-2]
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var bar;
bar = "abcdefghij";
bar.slice(2);
bar.slice(2,-2);
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%%py2js
# Subscripting
foo = {'bar': 3}
foo['bar']
foo.bar  # Works in JS, but not in Python
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var foo;
foo = ({bar: 3});
foo["bar"];
foo.bar;

格式化字符串

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%%py2js
"value: %f" % val

# 卧槽, 生成的代码太长了
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var _pyfunc_format = function (v, fmt) {  // nargs: 2
    fmt = fmt.toLowerCase();
    var s = String(v);
    if (fmt.indexOf('!r') >= 0) {
        try { s = JSON.stringify(v); } catch (e) { s = undefined; }
        if (typeof s === 'undefined') { s = v._IS_COMPONENT ? v.id : String(v); }
    }
    var i0 = fmt.indexOf(':');
    if (i0 < 0) {
    } else if (fmt.indexOf('i', i0) > i0) { // integer formatting
        s = Number.parseInt(v).toFixed(0);
    } else if (fmt.indexOf('f', i0) > i0) {  // float formatting
        v = Number.parseFloat(v);
        var spec = fmt.slice(i0+1, fmt.indexOf('f', i0));
        var decimals = 6;
        if (spec.indexOf('.') >= 0) {
            var decimals = Number(spec.slice(spec.indexOf('.')+1));
        }
        s = v.toFixed(decimals);
    } else if (fmt.indexOf('e', i0) > i0) {  // exp formatting
        v = Number.parseFloat(v);
        var precision = 6;
        var spec = fmt.slice(i0+1, fmt.indexOf('e', i0));
        if (spec.indexOf('.') >= 0) {
            precision = Number(spec.slice(spec.indexOf('.')+1)) || 1;
        }
        s = v.toExponential(precision);
    } else if (fmt.indexOf('g', i0) > i0) {  // "general" formatting
        v = Number.parseFloat(v);
        var precision = 6;
        var spec = fmt.slice(i0+1, fmt.indexOf('g', i0));
        if (spec.indexOf('.') >= 0) {
            precision = Number(spec.slice(spec.indexOf('.')+1)) || 1;
        }
        // Exp or decimal?
        s = v.toExponential(precision-1);
        var s1 = s.slice(0, s.indexOf('e')), s2 = s.slice(s.indexOf('e'));
        if (s2.length == 3) { s2 = 'e' + s2[1] + '0' + s2[2]; }
        var exp = Number(s2.slice(1));
        if (exp >= -4 && exp < precision) { s1=v.toPrecision(precision); s2=''; }
        // Skip trailing zeros and dot
        var j = s1.length-1;
        while (j>0 && s1[j] == '0') { j-=1; }
        s1 = s1.slice(0, j+1);
        if (s1.endsWith('.')) { s1 = s1.slice(0, s1.length-1); }
        s = s1 + s2;
    }
    if (i0 >= 0 && v > 0) {
        if (fmt[i0+1] == '+') { s = '+' + s; }
        if (fmt[i0+1] == ' ') { s = ' ' + s; }
    }
    return s;
};
var _pymeth_format = function () {
    if (this.constructor !== String) return this.format.apply(this, arguments);
    var parts = [], i = 0, i1, i2;
    var itemnr = -1;
    while (i < this.length) {
        // find opening
        i1 = this.indexOf('{', i);
        if (i1 < 0 || i1 == this.length-1) { break; }
        if (this[i1+1] == '{') {parts.push(this.slice(i, i1+1)); i = i1 + 2; continue;}
        // find closing
        i2 = this.indexOf('}', i1);
        if (i2 < 0) { break; }
        // parse
        itemnr += 1;
        var fmt = this.slice(i1+1, i2);
        var index = fmt.split(':')[0].split('!')[0];
        index = index? Number(index) : itemnr
        var s = _pyfunc_format(arguments[index], fmt);
        parts.push(this.slice(i, i1), s);
        i = i2 + 1;
    }
    parts.push(this.slice(i));
    return parts.join('');
};
_pymeth_format.call("value: {:f}", val);
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%%py2js

'{a}'.format(a)
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var _pyfunc_format = function (v, fmt) {  // nargs: 2
    fmt = fmt.toLowerCase();
    var s = String(v);
    if (fmt.indexOf('!r') >= 0) {
        try { s = JSON.stringify(v); } catch (e) { s = undefined; }
        if (typeof s === 'undefined') { s = v._IS_COMPONENT ? v.id : String(v); }
    }
    var i0 = fmt.indexOf(':');
    if (i0 < 0) {
    } else if (fmt.indexOf('i', i0) > i0) { // integer formatting
        s = Number.parseInt(v).toFixed(0);
    } else if (fmt.indexOf('f', i0) > i0) {  // float formatting
        v = Number.parseFloat(v);
        var spec = fmt.slice(i0+1, fmt.indexOf('f', i0));
        var decimals = 6;
        if (spec.indexOf('.') >= 0) {
            var decimals = Number(spec.slice(spec.indexOf('.')+1));
        }
        s = v.toFixed(decimals);
    } else if (fmt.indexOf('e', i0) > i0) {  // exp formatting
        v = Number.parseFloat(v);
        var precision = 6;
        var spec = fmt.slice(i0+1, fmt.indexOf('e', i0));
        if (spec.indexOf('.') >= 0) {
            precision = Number(spec.slice(spec.indexOf('.')+1)) || 1;
        }
        s = v.toExponential(precision);
    } else if (fmt.indexOf('g', i0) > i0) {  // "general" formatting
        v = Number.parseFloat(v);
        var precision = 6;
        var spec = fmt.slice(i0+1, fmt.indexOf('g', i0));
        if (spec.indexOf('.') >= 0) {
            precision = Number(spec.slice(spec.indexOf('.')+1)) || 1;
        }
        // Exp or decimal?
        s = v.toExponential(precision-1);
        var s1 = s.slice(0, s.indexOf('e')), s2 = s.slice(s.indexOf('e'));
        if (s2.length == 3) { s2 = 'e' + s2[1] + '0' + s2[2]; }
        var exp = Number(s2.slice(1));
        if (exp >= -4 && exp < precision) { s1=v.toPrecision(precision); s2=''; }
        // Skip trailing zeros and dot
        var j = s1.length-1;
        while (j>0 && s1[j] == '0') { j-=1; }
        s1 = s1.slice(0, j+1);
        if (s1.endsWith('.')) { s1 = s1.slice(0, s1.length-1); }
        s = s1 + s2;
    }
    if (i0 >= 0 && v > 0) {
        if (fmt[i0+1] == '+') { s = '+' + s; }
        if (fmt[i0+1] == ' ') { s = ' ' + s; }
    }
    return s;
};
var _pymeth_format = function () {
    if (this.constructor !== String) return this.format.apply(this, arguments);
    var parts = [], i = 0, i1, i2;
    var itemnr = -1;
    while (i < this.length) {
        // find opening
        i1 = this.indexOf('{', i);
        if (i1 < 0 || i1 == this.length-1) { break; }
        if (this[i1+1] == '{') {parts.push(this.slice(i, i1+1)); i = i1 + 2; continue;}
        // find closing
        i2 = this.indexOf('}', i1);
        if (i2 < 0) { break; }
        // parse
        itemnr += 1;
        var fmt = this.slice(i1+1, i2);
        var index = fmt.split(':')[0].split('!')[0];
        index = index? Number(index) : itemnr
        var s = _pyfunc_format(arguments[index], fmt);
        parts.push(this.slice(i, i1), s);
        i = i2 + 1;
    }
    parts.push(this.slice(i));
    return parts.join('');
};
_pymeth_format.call("{a}", a);

赋值操作

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%%py2js

bar.foo = 3
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bar.foo = 3;
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%%py2js
a = 1, 2, 3
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var a;
a = [1, 2, 3];
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%%py2js
a1, a2, a3 = a
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var a1, a2, a3, stub1_;
stub1_ = a;
a1 = stub1_[0];a2 = stub1_[1];a3 = stub1_[2];
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%%py2js

del bar.foo
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delete bar.foo;
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%%py2js
# 大写字母开头, 实例化这个类
foo = Foo()
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var foo;
foo = new Foo();

比较

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%%py2js

foo is bar
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foo === bar;
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%%py2js

foo == bar
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var _pyfunc_op_equals = function op_equals (a, b) { // nargs: 2
    if (a == null || b == null) {
    } else if (Array.isArray(a) && Array.isArray(b)) {
        var i = 0, iseq = a.length == b.length;
        while (iseq && i < a.length) {iseq = op_equals(a[i], b[i]); i+=1;}
        return iseq;
    } else if (a.constructor === Object && b.constructor === Object) {
        var akeys = Object.keys(a), bkeys = Object.keys(b);
        akeys.sort(); bkeys.sort();
        var i=0, k, iseq = op_equals(akeys, bkeys);
        while (iseq && i < akeys.length)
            {k=akeys[i]; iseq = op_equals(a[k], b[k]); i+=1;}
        return iseq;
    } return a == b;
};
_pyfunc_op_equals(foo, bar);
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%%py2js
# 深度比较, 和js不同
(2, 3, 4) == (2, 3, 4)
(2, 3) in [(1,2), (2,3), (3,4)]
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var _pyfunc_op_contains = function op_contains (a, b) { // nargs: 2
    if (b == null) {
    } else if (Array.isArray(b)) {
        for (var i=0; i<b.length; i++) {if (_pyfunc_op_equals(a, b[i]))
                                           return true;}
        return false;
    } else if (b.constructor === Object) {
        for (var k in b) {if (a == k) return true;}
        return false;
    } else if (b.constructor == String) {
        return b.indexOf(a) >= 0;
    } var e = Error('Not a container: ' + b); e.name='TypeError'; throw e;
};
var _pyfunc_op_equals = function op_equals (a, b) { // nargs: 2
    if (a == null || b == null) {
    } else if (Array.isArray(a) && Array.isArray(b)) {
        var i = 0, iseq = a.length == b.length;
        while (iseq && i < a.length) {iseq = op_equals(a[i], b[i]); i+=1;}
        return iseq;
    } else if (a.constructor === Object && b.constructor === Object) {
        var akeys = Object.keys(a), bkeys = Object.keys(b);
        akeys.sort(); bkeys.sort();
        var i=0, k, iseq = op_equals(akeys, bkeys);
        while (iseq && i < akeys.length)
            {k=akeys[i]; iseq = op_equals(a[k], b[k]); i+=1;}
        return iseq;
    } return a == b;
};
_pyfunc_op_equals([2, 3, 4], [2, 3, 4]);
_pyfunc_op_contains([2, 3], ([[1, 2], [2, 3], [3, 4]]));
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%%py2js

foo is undefined
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foo === undefined;
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%%py2js

"foo" in "this has foo in it"
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var _pyfunc_op_contains = function op_contains (a, b) { // nargs: 2
    if (b == null) {
    } else if (Array.isArray(b)) {
        for (var i=0; i<b.length; i++) {if (_pyfunc_op_equals(a, b[i]))
                                           return true;}
        return false;
    } else if (b.constructor === Object) {
        for (var k in b) {if (a == k) return true;}
        return false;
    } else if (b.constructor == String) {
        return b.indexOf(a) >= 0;
    } var e = Error('Not a container: ' + b); e.name='TypeError'; throw e;
};
var _pyfunc_op_equals = function op_equals (a, b) { // nargs: 2
    if (a == null || b == null) {
    } else if (Array.isArray(a) && Array.isArray(b)) {
        var i = 0, iseq = a.length == b.length;
        while (iseq && i < a.length) {iseq = op_equals(a[i], b[i]); i+=1;}
        return iseq;
    } else if (a.constructor === Object && b.constructor === Object) {
        var akeys = Object.keys(a), bkeys = Object.keys(b);
        akeys.sort(); bkeys.sort();
        var i=0, k, iseq = op_equals(akeys, bkeys);
        while (iseq && i < akeys.length)
            {k=akeys[i]; iseq = op_equals(a[k], b[k]); i+=1;}
        return iseq;
    } return a == b;
};
_pyfunc_op_contains("foo", "this has foo in it");
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%%py2js

3 in [0, 1, 2, 3, 4]
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var _pyfunc_op_contains = function op_contains (a, b) { // nargs: 2
    if (b == null) {
    } else if (Array.isArray(b)) {
        for (var i=0; i<b.length; i++) {if (_pyfunc_op_equals(a, b[i]))
                                           return true;}
        return false;
    } else if (b.constructor === Object) {
        for (var k in b) {if (a == k) return true;}
        return false;
    } else if (b.constructor == String) {
        return b.indexOf(a) >= 0;
    } var e = Error('Not a container: ' + b); e.name='TypeError'; throw e;
};
var _pyfunc_op_equals = function op_equals (a, b) { // nargs: 2
    if (a == null || b == null) {
    } else if (Array.isArray(a) && Array.isArray(b)) {
        var i = 0, iseq = a.length == b.length;
        while (iseq && i < a.length) {iseq = op_equals(a[i], b[i]); i+=1;}
        return iseq;
    } else if (a.constructor === Object && b.constructor === Object) {
        var akeys = Object.keys(a), bkeys = Object.keys(b);
        akeys.sort(); bkeys.sort();
        var i=0, k, iseq = op_equals(akeys, bkeys);
        while (iseq && i < akeys.length)
            {k=akeys[i]; iseq = op_equals(a[k], b[k]); i+=1;}
        return iseq;
    } return a == b;
};
_pyfunc_op_contains(3, [0, 1, 2, 3, 4]);

Truthy和Falsy

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%%py2js

# 这些值都被判定为false

# These evaluate to False:
0
NaN
""  # empty string
None  # JS null
undefined
[]
{}
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0;
NaN;
"";
null;
undefined;
[];
({});
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%%py2js

# 支持这样的操作
a = []
a = a or [1]  # a is now [1]
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var _pyfunc_truthy = function (v) {
    if (v === null || typeof v !== "object") {return v;}
    else if (v.length !== undefined) {return v.length ? v : false;}
    else if (v.byteLength !== undefined) {return v.byteLength ? v : false;}
    else if (v.constructor !== Object) {return true;}
    else {return Object.getOwnPropertyNames(v).length ? v : false;}
};
var a;
a = [];
a = _pyfunc_truthy(a) || [1];

函数操作

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%%py2js

# Business as usual
foo(a, b)
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foo(a, b);
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%%py2js

# 支持 args (不支持 **kwargs)
foo(*a)
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foo.apply(null, a);

if语句

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%%py2js


if val > 7:
    result = 42
elif val > 1:
    result = 1
else:
    result = 0
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var result;
if ((val > 7)) {
    result = 42;
} else if ((val > 1)) {
    result = 1;
} else {
    result = 0;
}

循环

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%%py2js

val = 0
while val < 10:
    val += 1
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var _pyfunc_op_add = function (a, b) { // nargs: 2
    if (Array.isArray(a) && Array.isArray(b)) {
        return a.concat(b);
    } return a + b;
};
var val;
val = 0;
while (val < 10) {
    val = _pyfunc_op_add(val, 1);
}
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%%py2js

# Using range() yields true for-loops
for i in range(10):
    print(i)
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var i;
for (i = 0; i < 10; i += 1) {
    console.log(i);
}
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%%py2js

for i in range(100, 10, -2):
    print(i)
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var i;
for (i = 100; i > 10; i += -2) {
    console.log(i);
}
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%%py2js

# One way to iterate over an array
for i in range(len(arr)):
    print(arr[i])
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var i;
for (i = 0; i < arr.length; i += 1) {
    console.log(arr[i]);
}
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%%py2js
# But this is equally valid (and fast)
for element in arr:
    print(element)
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var element, stub1_seq, stub2_itr;
stub1_seq = arr;
if ((typeof stub1_seq === "object") && (!Array.isArray(stub1_seq))) { stub1_seq = Object.keys(stub1_seq);}
for (stub2_itr = 0; stub2_itr < stub1_seq.length; stub2_itr += 1) {
    element = stub1_seq[stub2_itr];
    console.log(element);
}
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%%py2js

# 遍历字符串
for char in "foo bar":
    print(c)
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var char, stub1_seq, stub2_itr;
stub1_seq = "foo bar";
if ((typeof stub1_seq === "object") && (!Array.isArray(stub1_seq))) { stub1_seq = Object.keys(stub1_seq);}
for (stub2_itr = 0; stub2_itr < stub1_seq.length; stub2_itr += 1) {
    char = stub1_seq[stub2_itr];
    console.log(c);
}
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%%py2js

# 更复杂的遍历
for i, j in [[1, 2], [3, 4]]:
    print(i+j)
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var _pyfunc_op_add = function (a, b) { // nargs: 2
    if (Array.isArray(a) && Array.isArray(b)) {
        return a.concat(b);
    } return a + b;
};
var i, j, stub1_seq, stub2_itr, stub3_tgt;
stub1_seq = [[1, 2], [3, 4]];
if ((typeof stub1_seq === "object") && (!Array.isArray(stub1_seq))) { stub1_seq = Object.keys(stub1_seq);}
for (stub2_itr = 0; stub2_itr < stub1_seq.length; stub2_itr += 1) {
    stub3_tgt = stub1_seq[stub2_itr];
    i = stub3_tgt[0]; j = stub3_tgt[1];
    console.log(_pyfunc_op_add(i, j));
}

支持用于迭代的Buildin函数：enumerate, zip, reversed, sorted, filter, map

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%%py2js

for i, x in enumerate(foo):
    print(i, x)
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var _pyfunc_enumerate = function (iter) { // nargs: 1
    var i, res=[];
    if ((typeof iter==="object") && (!Array.isArray(iter))) {iter = Object.keys(iter);}
    for (i=0; i<iter.length; i++) {res.push([i, iter[i]]);}
    return res;
};
var i, stub1_seq, stub2_itr, stub3_tgt, x;
stub1_seq = _pyfunc_enumerate(foo);
if ((typeof stub1_seq === "object") && (!Array.isArray(stub1_seq))) { stub1_seq = Object.keys(stub1_seq);}
for (stub2_itr = 0; stub2_itr < stub1_seq.length; stub2_itr += 1) {
    stub3_tgt = stub1_seq[stub2_itr];
    i = stub3_tgt[0]; x = stub3_tgt[1];
    console.log(i + " " + x);
}
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%%py2js

for a, b in zip(foo, bar):
    pass
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var _pyfunc_zip = function () { // nargs: 2 3 4 5 6 7 8 9
    var i, j, tup, arg, args = [], res = [], len = 1e20;
    for (i=0; i<arguments.length; i++) {
        arg = arguments[i];
        if ((typeof arg==="object") && (!Array.isArray(arg))) {arg = Object.keys(arg);}
        args.push(arg);
        len = Math.min(len, arg.length);
    }
    for (j=0; j<len; j++) {
        tup = []
        for (i=0; i<args.length; i++) {tup.push(args[i][j]);}
        res.push(tup);
    }
    return res;
};
var a, b, stub1_seq, stub2_itr, stub3_tgt;
stub1_seq = _pyfunc_zip(foo, bar);
if ((typeof stub1_seq === "object") && (!Array.isArray(stub1_seq))) { stub1_seq = Object.keys(stub1_seq);}
for (stub2_itr = 0; stub2_itr < stub1_seq.length; stub2_itr += 1) {
    stub3_tgt = stub1_seq[stub2_itr];
    a = stub3_tgt[0]; b = stub3_tgt[1];
}
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%%py2js

for x in reversed(sorted(foo)):
    pass
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var _pyfunc_reversed = function (iter) { // nargs: 1
    if ((typeof iter==="object") && (!Array.isArray(iter))) {iter = Object.keys(iter);}
    return iter.slice().reverse();
};
var _pyfunc_sorted = function (iter, key, reverse) { // nargs: 1 2 3
    if ((typeof iter==="object") && (!Array.isArray(iter))) {iter = Object.keys(iter);}
    var comp = function (a, b) {a = key(a); b = key(b);
        if (a<b) {return -1;} if (a>b) {return 1;} return 0;};
    comp = Boolean(key) ? comp : undefined; 
    iter = iter.slice().sort(comp);
    if (reverse) iter.reverse();
    return iter;
};
var stub1_seq, stub2_itr, x;
stub1_seq = _pyfunc_reversed(_pyfunc_sorted(foo, undefined, false));
if ((typeof stub1_seq === "object") && (!Array.isArray(stub1_seq))) { stub1_seq = Object.keys(stub1_seq);}
for (stub2_itr = 0; stub2_itr < stub1_seq.length; stub2_itr += 1) {
    x = stub1_seq[stub2_itr];
}
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%%py2js

for x in map(lambda x: x+1, foo):
    pass
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var _pyfunc_map = function (func, iter) { // nargs: 2
    if (typeof func === "undefined" || func === null) {func = function(x) {return x;}}
    if ((typeof iter==="object") && (!Array.isArray(iter))) {iter = Object.keys(iter);}
    return iter.map(func);
};
var stub1_seq, stub2_itr, x;
stub1_seq = _pyfunc_map((function (x) {return x + 1;}), foo);
if ((typeof stub1_seq === "object") && (!Array.isArray(stub1_seq))) { stub1_seq = Object.keys(stub1_seq);}
for (stub2_itr = 0; stub2_itr < stub1_seq.length; stub2_itr += 1) {
    x = stub1_seq[stub2_itr];
}
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%%py2js

for x in filter(lambda x: x>0, foo):
    pass
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var _pyfunc_filter = function (func, iter) { // nargs: 2
    if (typeof func === "undefined" || func === null) {func = function(x) {return x;}}
    if ((typeof iter==="object") && (!Array.isArray(iter))) {iter = Object.keys(iter);}
    return iter.filter(func);
};
var stub1_seq, stub2_itr, x;
stub1_seq = _pyfunc_filter((function (x) {return x > 0;}), foo);
if ((typeof stub1_seq === "object") && (!Array.isArray(stub1_seq))) { stub1_seq = Object.keys(stub1_seq);}
for (stub2_itr = 0; stub2_itr < stub1_seq.length; stub2_itr += 1) {
    x = stub1_seq[stub2_itr];
}

list 推导

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%%py2js

# List comprehensions just work
x = [i*2 for i in some_array if i>0]
y = [i*j for i in a for j in b]
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var _pyfunc_op_mult = function (a, b) { // nargs: 2
    if ((typeof a === 'number') + (typeof b === 'number') === 1) {
        if (a.constructor === String) return _pymeth_repeat.call(a, b);
        if (b.constructor === String) return _pymeth_repeat.call(b, a);
        if (Array.isArray(b)) {var t=a; a=b; b=t;}
        if (Array.isArray(a)) {
            var res = []; for (var i=0; i<b; i++) res = res.concat(a);
            return res;
        }
    } return a * b;
};
var _pymeth_repeat = function(count) { // nargs: 0
    if (this.repeat) return this.repeat(count);
    if (count < 1) return '';
    var result = '', pattern = this.valueOf();
    while (count > 1) {
        if (count & 1) result += pattern;
        count >>= 1, pattern += pattern;
    }
    return result + pattern;
};
var stub1_, stub1_i, stub1_i0, stub1_iter0, stub2_, stub2_i, stub2_i0, stub2_i1, stub2_iter0, stub2_iter1, stub2_j, x, y;
stub1_ = [];stub1_iter0 = some_array;if ((typeof stub1_iter0 === "object") && (!Array.isArray(stub1_iter0))) {stub1_iter0 = Object.keys(stub1_iter0);}for (stub1_i0=0; stub1_i0<stub1_iter0.length; stub1_i0++) {stub1_i = stub1_iter0[stub1_i0];if (!((stub1_i > 0))) {continue;}{stub1_.push(_pyfunc_op_mult(stub1_i, 2));}}
x = stub1_;
stub2_ = [];stub2_iter0 = a;if ((typeof stub2_iter0 === "object") && (!Array.isArray(stub2_iter0))) {stub2_iter0 = Object.keys(stub2_iter0);}for (stub2_i0=0; stub2_i0<stub2_iter0.length; stub2_i0++) {stub2_i = stub2_iter0[stub2_i0];stub2_iter1 = b;if ((typeof stub2_iter1 === "object") && (!Array.isArray(stub2_iter1))) {stub2_iter1 = Object.keys(stub2_iter1);}for (stub2_i1=0; stub2_i1<stub2_iter1.length; stub2_i1++) {stub2_j = stub2_iter1[stub2_i1];{stub2_.push(_pyfunc_op_mult(stub2_i, stub2_j));}}}
y = stub2_;

定义函数

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%%py2js

def display(val):
    print(val)
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var display;
display = function flx_display (val) {
    console.log(val);
    return null;
};

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%%py2js

# 支持 *args
def foo(x, *values):
    bar(x+1, *values)
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var foo;
foo = function flx_foo (x) {
    var values;
    values = Array.prototype.slice.call(arguments, 1);
    bar.apply(null, [].concat([x + 1], values));
    return null;
};

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%%py2js

# 想要混编JavaScript, 也可以使用RawJS
def bar(a, b):
    RawJS('''
    var c = 4;
    return a + b + c;
    ''')
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var bar;
bar = function flx_bar (a, b) {
    var c = 4;
    return a + b + c;;
    return null;
};

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%%py2js

# Lambda 表达式
foo = lambda x: x**2
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var foo;
foo = function (x) {return Math.pow(x, 2);};

定义类

类被转换为JavaScript原型类paragigm，这意味着它们应该可以很好地与其他JS库一起使用。支持继承，但不支持多重继承。此外，super（）的工作方式与Python 3相同。

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%%py2js
class Foo:
    a_class_attribute = 4
    def __init__(self):
        self.x = 3
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var _pyfunc_op_instantiate = function (ob, args) { // nargs: 2
    if ((typeof ob === "undefined") ||
            (typeof window !== "undefined" && window === ob) ||
            (typeof global !== "undefined" && global === ob))
            {throw "Class constructor is called as a function.";}
    for (var name in ob) {
        if (Object[name] === undefined &&
            typeof ob[name] === 'function' && !ob[name].nobind) {
            ob[name] = ob[name].bind(ob);
            ob[name].__name__ = name;
        }
    }
    if (ob.__init__) {
        ob.__init__.apply(ob, args);
    }
};
var Foo;
Foo = function () {
    _pyfunc_op_instantiate(this, arguments);
}
Foo.prototype._base_class = Object;
Foo.prototype.__name__ = "Foo";

Foo.prototype.a_class_attribute = 4;
Foo.prototype.__init__ = function () {
    this.x = 3;
    return null;
};


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%%py2js

class Bar(Foo):
    def __init__(self):
        super.__init__()
        self.x += 1
    def add1(self):
        self.x += 1
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var _pyfunc_op_add = function (a, b) { // nargs: 2
    if (Array.isArray(a) && Array.isArray(b)) {
        return a.concat(b);
    } return a + b;
};
var _pyfunc_op_instantiate = function (ob, args) { // nargs: 2
    if ((typeof ob === "undefined") ||
            (typeof window !== "undefined" && window === ob) ||
            (typeof global !== "undefined" && global === ob))
            {throw "Class constructor is called as a function.";}
    for (var name in ob) {
        if (Object[name] === undefined &&
            typeof ob[name] === 'function' && !ob[name].nobind) {
            ob[name] = ob[name].bind(ob);
            ob[name].__name__ = name;
        }
    }
    if (ob.__init__) {
        ob.__init__.apply(ob, args);
    }
};
var Bar;
Bar = function () {
    _pyfunc_op_instantiate(this, arguments);
}
Bar.prototype = Object.create(Foo.prototype);
Bar.prototype._base_class = Foo.prototype;
Bar.prototype.__name__ = "Bar";

Bar.prototype.__init__ = function () {
    super.__init__();
    this.x = _pyfunc_op_add(this.x, 1);
    return null;
};

Bar.prototype.add1 = function () {
    this.x = _pyfunc_op_add(this.x, 1);
    return null;
};


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%%py2js

# 实例化和调用方法
b = Bar()
setTimeout(b.add1, 1000)
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var b;
b = new Bar();
setTimeout(b.add1, 1000);
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%%py2js
# Functions defined in methods (and that do not start with self or this)
# have ``this`` bound the the same object.
class Spam(Bar):
    def add_later(self):
        setTimeout(lambda ev: self.add1(), 1000)
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var _pyfunc_op_instantiate = function (ob, args) { // nargs: 2
    if ((typeof ob === "undefined") ||
            (typeof window !== "undefined" && window === ob) ||
            (typeof global !== "undefined" && global === ob))
            {throw "Class constructor is called as a function.";}
    for (var name in ob) {
        if (Object[name] === undefined &&
            typeof ob[name] === 'function' && !ob[name].nobind) {
            ob[name] = ob[name].bind(ob);
            ob[name].__name__ = name;
        }
    }
    if (ob.__init__) {
        ob.__init__.apply(ob, args);
    }
};
var Spam;
Spam = function () {
    _pyfunc_op_instantiate(this, arguments);
}
Spam.prototype = Object.create(Bar.prototype);
Spam.prototype._base_class = Bar.prototype;
Spam.prototype.__name__ = "Spam";

Spam.prototype.add_later = function () {
    setTimeout((function (ev) {return this.add1();}).bind(this), 1000);
    return null;
};


异常

引发的异常将转换为JavaScript Error对象，其name属性设置为引发的异常类型。捕获异常时，将检查name属性（如果它是一个Error对象)。您可以raise字符串或任何其他类型的对象，但您只能捕获Error对象。

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%%py2js

# 抛出异常
raise SomeError('asd')
raise AnotherError()
raise "In JS you can throw anything"
raise 4
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var _pyfunc_op_error = function (etype, msg) { // nargs: 2
    var e = new Error(etype + ': ' + msg);
    e.name = etype
    return e;
};
var err_0;
throw _pyfunc_op_error('SomeError', "asd");
throw _pyfunc_op_error('AnotherError', "");
throw "In JS you can throw anything";
throw 4;
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%%py2js
# Assertions 能正常工作
assert foo == 3
assert bar == 4, "bar should be 4"
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var _pyfunc_op_equals = function op_equals (a, b) { // nargs: 2
    if (a == null || b == null) {
    } else if (Array.isArray(a) && Array.isArray(b)) {
        var i = 0, iseq = a.length == b.length;
        while (iseq && i < a.length) {iseq = op_equals(a[i], b[i]); i+=1;}
        return iseq;
    } else if (a.constructor === Object && b.constructor === Object) {
        var akeys = Object.keys(a), bkeys = Object.keys(b);
        akeys.sort(); bkeys.sort();
        var i=0, k, iseq = op_equals(akeys, bkeys);
        while (iseq && i < akeys.length)
            {k=akeys[i]; iseq = op_equals(a[k], b[k]); i+=1;}
        return iseq;
    } return a == b;
};
var _pyfunc_op_error = function (etype, msg) { // nargs: 2
    var e = new Error(etype + ': ' + msg);
    e.name = etype
    return e;
};
if (!(_pyfunc_op_equals(foo, 3))) { throw _pyfunc_op_error('AssertionError', "_pyfunc_op_equals(foo, 3)");}
if (!(_pyfunc_op_equals(bar, 4))) { throw _pyfunc_op_error('AssertionError', "\"bar should be 4\"");}
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%%py2js

# 捕捉异常
try:
    raise IndexError('blabla')
except IndexError as err:
    print(err)
except Exception:
   print('something went wrong')
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var _pyfunc_op_error = function (etype, msg) { // nargs: 2
    var e = new Error(etype + ': ' + msg);
    e.name = etype
    return e;
};
var err, err_1;
try {
    throw _pyfunc_op_error('IndexError', "blabla");
} catch(err_1) {
    if (err_1 instanceof Error && err_1.name === "IndexError") {
        err = err_1;
        console.log(err);
    } else {
        console.log("something went wrong");
    }
}

python内置函数

大多数buildin函数（在JS中有意义的）会自动转换为JavaScript的内建函数：isinstance，issubclass，callable，hasattr，getattr，setattr，delattr，print，len，max，min，chr，ord，dict，list，tuple，range， pow，sum，round，int，float，str，bool，abs，divmod，all，any，enumerate，zip，reversed，sorted，filtered，map。

此外，还实现了list，dict和str的所有方法（str方法除外：encode，decode，format，format_map，isdecimal，isdigit，isprintable，maketrans）。

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%%py2js
# Printing 能正常工作
print('some test')
print(a, b, c, sep='-')
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console.log("some test");
console.log(a + "-" + b + "-" + c);
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%%py2js
# 获取字符串长度
len(foo)
1
foo.length;
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%%py2js
# 保留小数和绝对值
round(foo)  # round to nearest integer
int(foo)  # round towards 0 as in Python
abs(foo)
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var _pyfunc_abs = Math.abs;
var _pyfunc_int = function (x) { // nargs: 1
    return x<0 ? Math.ceil(x): Math.floor(x);
};
var _pyfunc_round = Math.round;
_pyfunc_round(foo);
_pyfunc_int(foo);
_pyfunc_abs(foo);
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%%py2js
# 最大值和最小值
min(foo)
min(a, b, c)
max(foo)
max(a, b, c)
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Math.min.apply(null, foo);
Math.min(a, b, c);
Math.max.apply(null, foo);
Math.max(a, b, c);
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%%py2js
# 求余数
a, b = divmod(100, 7)  # -> 14, 2
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var _pyfunc_divmod = function (x, y) { // nargs: 2
    var m = x % y; return [(x-m)/y, m];
};
var a, b, stub1_;
stub1_ = _pyfunc_divmod(100, 7);
a = stub1_[0];b = stub1_[1];
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%%py2js
# 聚合
sum(foo)
all(foo)
any(foo)
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var _pyfunc_all = function (x) { // nargs: 1
    for (var i=0; i<x.length; i++) {
        if (!_pyfunc_truthy(x[i])){return false;}
    } return true;
};
var _pyfunc_any = function (x) { // nargs: 1
    for (var i=0; i<x.length; i++) {
        if (_pyfunc_truthy(x[i])){return true;}
    } return false;
};
var _pyfunc_sum = function (x) {  // nargs: 1
    return x.reduce(function(a, b) {return a + b;});
};
var _pyfunc_truthy = function (v) {
    if (v === null || typeof v !== "object") {return v;}
    else if (v.length !== undefined) {return v.length ? v : false;}
    else if (v.byteLength !== undefined) {return v.byteLength ? v : false;}
    else if (v.constructor !== Object) {return true;}
    else {return Object.getOwnPropertyNames(v).length ? v : false;}
};
_pyfunc_sum(foo);
_pyfunc_all(foo);
_pyfunc_any(foo);
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%%py2js
# 数据转换: numbers, bools and strings
str(s)
float(x)
bool(y)
int(z)  # this rounds towards zero like in Python
chr(65)  # -> 'A'
ord('A')  # -> 65
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var _pyfunc_bool = function (x) { // nargs: 1
    return Boolean(_pyfunc_truthy(x));
};
var _pyfunc_float = Number;
var _pyfunc_int = function (x) { // nargs: 1
    return x<0 ? Math.ceil(x): Math.floor(x);
};
var _pyfunc_str = String;
var _pyfunc_truthy = function (v) {
    if (v === null || typeof v !== "object") {return v;}
    else if (v.length !== undefined) {return v.length ? v : false;}
    else if (v.byteLength !== undefined) {return v.byteLength ? v : false;}
    else if (v.constructor !== Object) {return true;}
    else {return Object.getOwnPropertyNames(v).length ? v : false;}
};
_pyfunc_str(s);
_pyfunc_float(x);
_pyfunc_bool(y);
_pyfunc_int(z);
String.fromCharCode(65);
"A".charCodeAt(0);
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%%py2js
# 数据转换成 lists and dicts
dict([['foo', 1], ['bar', 2]])  # -> {'foo': 1, 'bar': 2}
list('abc')  # -> ['a', 'b', 'c']
dict(other_dict)  # make a copy
list(other_list)  # make copy
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var _pyfunc_dict = function (x) {
    var t, i, keys, r={};
    if (Array.isArray(x)) {
        for (i=0; i<x.length; i++) {
            t=x[i]; r[t[0]] = t[1];
        }
    } else {
        keys = Object.keys(x);
        for (i=0; i<keys.length; i++) {
            t=keys[i]; r[t] = x[t];
        }
    }
    return r;
};
var _pyfunc_list = function (x) {
    var r=[];
    if (typeof x==="object" && !Array.isArray(x)) {x = Object.keys(x)}
    for (var i=0; i<x.length; i++) {
        r.push(x[i]);
    }
    return r;
};
_pyfunc_dict(([["foo", 1], ["bar", 2]]));
_pyfunc_list("abc");
_pyfunc_dict(other_dict);
_pyfunc_list(other_list);

isinstance相关功能

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%%py2js
# 基本类型
isinstance(3, float)  # in JS there are no ints
isinstance('', str)
isinstance([], list)
isinstance({}, dict)
isinstance(foo, types.FunctionType)
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Object.prototype.toString.call(3).slice(8,-1).toLowerCase() === 'number';
Object.prototype.toString.call("").slice(8,-1).toLowerCase() === 'string';
Array.isArray([]);
Object.prototype.toString.call(({})).slice(8,-1).toLowerCase() === 'object';
Object.prototype.toString.call(foo).slice(8,-1).toLowerCase() === 'function';
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%%py2js
# 也可以用JS的字符串
isinstance(3, 'number')
isinstance('', 'string')
isinstance([], 'array')
isinstance({}, 'object')
isinstance(foo, 'function')
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Object.prototype.toString.call(3).slice(8,-1).toLowerCase() === 'number';
Object.prototype.toString.call("").slice(8,-1).toLowerCase() === 'string';
Array.isArray([]);
Object.prototype.toString.call(({})).slice(8,-1).toLowerCase() === 'object';
Object.prototype.toString.call(foo).slice(8,-1).toLowerCase() === 'function';
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%%py2js
# 可以用于自定义类型.
isinstance(x, MyClass)
isinstance(x, 'MyClass')  # equivalent
isinstance(x, 'Object')  # also yields true (subclass of Object)
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x instanceof MyClass;
x instanceof MyClass;
Object.prototype.toString.call(x).slice(8,-1).toLowerCase() === 'object';
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%%py2js
# issubclass 也能正常工作
issubclass(Foo, Bar)
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(Foo.prototype instanceof Bar);
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%%py2js
# callable也能正常工作
callable(foo)
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(typeof foo === "function");

hasattr, getattr, setattr and delattr

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%%py2js

a = {'foo': 1, 'bar': 2}
hasattr(a, 'foo')  # -> True
hasattr(a, 'fooo')  # -> False
hasattr(null, 'foo')  # -> False
getattr(a, 'foo')  # -> 1
getattr(a, 'fooo')  # -> raise AttributeError
getattr(a, 'fooo', 3)  # -> 3
getattr(null, 'foo', 3)  # -> 3
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var _pyfunc_getattr = function (ob, name, deflt) { // nargs: 2 3
    var has_attr = ob !== undefined && ob !== null && ob[name] !== undefined;
    if (has_attr) {return ob[name];}
    else if (arguments.length == 3) {return deflt;}
    else {var e = Error(name); e.name='AttributeError'; throw e;}
};
var _pyfunc_hasattr = function (ob, name) { // nargs: 2
    return (ob !== undefined) && (ob !== null) && (ob[name] !== undefined);
};
var a;
a = ({foo: 1, bar: 2});
_pyfunc_hasattr(a, "foo");
_pyfunc_hasattr(a, "fooo");
_pyfunc_hasattr(null, "foo");
_pyfunc_getattr(a, "foo");
_pyfunc_getattr(a, "fooo");
_pyfunc_getattr(a, "fooo", 3);
_pyfunc_getattr(null, "foo", 3);
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%%py2js

setattr(a, 'foo', 2)
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var _pyfunc_setattr = function (ob, name, value) {  // nargs: 3
    ob[name] = value;
};
_pyfunc_setattr(a, "foo", 2);
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%%py2js

delattr(a, 'foo')
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var _pyfunc_delattr = function (ob, name) {  // nargs: 2
    delete ob[name];
};
_pyfunc_delattr(a, "foo");

使用JS专属功能

在Python模块中编写PyScript时，我们建议在使用特定JavaScript功能的地方，引用以window为前缀。其中window表示全局JS命名空间。所有全局JavaScript对象/函数和变量都自动成为window对象的成员。这有助于明确该功能是JS特有的，还有助于像flake8这样的静态代码分析工具。

除了window, flexx.pyscript 也提供 undefined, Inifinity, 和 NaN.

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%%py2js

def foo(a):
    return window.Math.cos(a)
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var foo;
foo = function flx_foo (a) {
    return window.Math.cos(a);
};

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