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blueloveTH 2023-04-23 13:31:46 +08:00
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--- ---
icon: book icon: book
order: 2 order: 2
label: Coding Style Guide label: Coding style guide
--- ---
# Coding Style Guide # Coding Style Guide

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---
icon: code
label: 'C++'
order: 10
---
For C++ developers, you can download the `pocketpy.h` on our GitHub release page.
https://github.com/blueloveTH/pocketpy/releases/latest
## Example
```cpp
#include "pocketpy.h"
using namespace pkpy;
int main(){
// Create a virtual machine
VM* vm = new VM(true);
// Hello world!
vm->exec("print('Hello world!')", "main.py", EXEC_MODE);
// Create a list
vm->exec("a = [1, 2, 3]", "main.py", EXEC_MODE);
// Eval the sum of the list
PyObject* result = vm->exec("sum(a)", "<eval>", EVAL_MODE);
std::cout << py_cast<i64>(vm, result); // 6
return 0;
}
```
## Interop with `PyObject*`
In PkPy, any python object is represented by a `PyObject*`.
+ `VAR(...)`,
create a `PyObject*` from a C type
+ `CAST(T, ...)`,
cast a `PyObject*` to a C type
+ `_CAST(T, ...)`,
cast a `PyObject*` to a C type, without type check
```cpp
PyObject* x = VAR(12); // cast a C int to PyObject*
int y = CAST(int, x); // cast a PyObject* to C int
PyObject* i = VAR("abc");
std::cout << CAST(Str, i); // abc
```
#### Types
| `PyObject` type | C type | note |
| ------------ | ---------------- | ---------------------- |
| `int` | `i64` | 62 bits integer |
| `float` | `f64` | 62 bits floating point |
| `str` | `pkpy::Str` | |
| `bool` | `bool` | |
| `list` | `pkpy::List` | |
| `tuple` | `pkpy::Tuple` | |
| `function` | `pkpy::Function` | |
| ... | ... | ... |
## Bind a Native Function
In `VM` class, there are 4 methods to bind native function.
+ `VM::bind_func<ARGC>`
+ `VM::bind_builtin_func<ARGC>`
+ `VM::bind_method<ARGC>`
+ `VM::bind_static_method<ARGC>`
They are all template methods, the template argument is a `int` number, indicating the argument count. For variadic arguments, use `-1`. For methods, `ARGC` do not include `self`.
!!!
Native functions do not support keyword arguments.
!!!
PkPy uses a universal C function pointer for native functions:
```cpp
typedef PyObject* (*NativeFuncC)(VM*, ArgsView);
```
The first argument is the pointer of `VM` instance.
The second argument is a view of an array. You can use `[]` operator to get the element. If you have specified `ARGC` other than `-1`, the interpreter will ensure `args.size() == ARGC`. No need to do size check.
The return value is a `PyObject*`, which should not be `nullptr`. If there is no return value, return `vm->None`.
This is an example of binding the `input()` function to the `builtins` module.
```cpp
VM* vm = pkpy_new_vm(true);
vm->bind_builtin_func<0>("input", [](VM* vm, ArgsView args){
static std::string line;
std::getline(std::cin, line);
return VAR(line);
});
// vvv function name
vm->bind_builtin_func<2>("add", [](VM* vm, ArgsView args){
// ^ argument count
i64 lhs = CAST(i64, args[0]);
i64 rhs = CAST(i64, args[1]);
return VAR(lhs + rhs);
});
```
## Call a Python Function
Use these to call a python function.
+ `PyObject* VM::call(PyObject* obj, ...)`
+ `PyObject* VM::call_method(PyObject* obj, StrName name, ...)`
For example, to create a `dict` object,
```cpp
PyObject* tp = vm->builtins->attr("dict");
PyObject* obj = vm->call(tp); // this is a `dict`
```
And set a key-value pair,
```cpp
vm->call_method(obj, "__setitem__", VAR("a"), VAR(5));
PyObject* ret = vm->call(obj, "__getitem__", VAR("a"));
std::cout << CAST(int, ret) << std::endl; // 5
```
## Attribute Access
There are 3 methods for this.
+ `PyObject* VM::getattr(PyObject*, StrName)`
+ `void VM::setattr(PyObject*, StrName, PyObject*)`
+ `PyObject* VM::get_unbound_method(PyObject*, StrName, PyObject**)`
## Wrapping a `struct` as `PyObject`
!!!
This feature is unstable.
!!!

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---
icon: code
label: Godot Engine
order: 2
---
## Introduction
PocketPy for Godot is integrated via [GDExtension](https://godotengine.org/article/introducing-gd-extensions).
!!!
GDExtension is a Godot 4.0 feature. Godot 3.x won't work.
!!!
Please see https://github.com/blueloveTH/godot-cpp/tree/master/pocketpy for details.
## Example
```gdscript
# main.gd
extends Node
func _ready():
# Create a virtual machine
var vm = pkpy.new_vm(false)
# Run a script
pkpy.vm_exec(vm, "print('Hello World!')")
# Read the output
var _o = pkpy.vm_read_output(vm)
# Parse the output
var res = JSON.parse_string(_o)
# Print the output
print(res["stdout"]) # "Hello World!\n"
```

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---
icon: code
label: 'Installation'
order: 100
---
You need to download `pocketpy.h` on our GitHub release page.
And `#include` it in your project.
https://github.com/blueloveTH/pocketpy/releases/latest
Alternatively, you can install it via vcpkg.io.
(Will be available soon)
```bash
vcpkg install pocketpy
```
## Example
```cpp
#include "pocketpy.h"
using namespace pkpy;
int main(){
// Create a virtual machine
VM* vm = new VM(true);
// Hello world!
vm->exec("print('Hello world!')", "main.py", EXEC_MODE);
// Create a list
vm->exec("a = [1, 2, 3]", "main.py", EXEC_MODE);
// Eval the sum of the list
PyObject* result = vm->exec("sum(a)", "<eval>", EVAL_MODE);
std::cout << CAST(int, result); // 6
return 0;
}
```

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---
icon: code
label: 'Interop with PyObject'
order: 90
---
Any python object is represented by a `PyObject*`.
+ `VAR(...)`,
create a `PyObject*` from a C type
+ `CAST(T, ...)`,
cast a `PyObject*` to a C type
+ `_CAST(T, ...)`,
cast a `PyObject*` to a C type, without type check
```cpp
PyObject* x = VAR(12); // cast a C int to PyObject*
int y = CAST(int, x); // cast a PyObject* to C int
PyObject* i = VAR("abc");
std::cout << CAST(Str, i); // abc
```
#### Types
| `PyObject` type | C type | note |
| ------------ | ---------------- | ---------------------- |
| `int` | `i64` | 62 bits integer |
| `float` | `f64` | 62 bits floating point |
| `str` | `pkpy::Str` | |
| `bool` | `bool` | |
| `list` | `pkpy::List` | |
| `tuple` | `pkpy::Tuple` | |
| `function` | `pkpy::Function` | |
| ... | ... | ... |

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---
icon: code
label: 'Attribute access'
order: 80
---
#### `PyObject* getattr(PyObject* obj, StrName name, bool throw_err=true)`
This method is equivalent to `getattr` in Python.
If the attribute is not found, it will return `nullptr`
or throw an `AttributeError` depending on the value of `throw_err`.
```cpp
// create a `int` object
PyObject* obj = VAR(1);
// get its `__add__` method, which is a `bound_method` object
PyObject* add = vm->getattr(obj, "__add__");
// call it (equivalent to `1 + 2`)
PyObject* ret = vm->call(add, VAR(2));
// get the result
int result = CAST(int, ret);
std::cout << result << std::endl; // 3
```
#### `void setattr(PyObject*, StrName, PyObject*)`
This method is equivalent to `setattr` in Python.
It raises `TypeError` if the object does not support attribute assignment.

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---
icon: code
label: 'Call a Python function'
order: 70
---
Use these to call a python function.
+ `PyObject* VM::call(PyObject* obj, ...)`
+ `PyObject* VM::call_method(PyObject* obj, StrName name, ...)`
For example, to create a `dict` object,
```cpp
PyObject* tp = vm->builtins->attr("dict");
PyObject* obj = vm->call(tp); // this is a `dict`
```
And set a key-value pair,
```cpp
vm->call_method(obj, "__setitem__", VAR("a"), VAR(5));
PyObject* ret = vm->call(obj, "__getitem__", VAR("a"));
std::cout << CAST(int, ret) << std::endl; // 5
```

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---
icon: code
label: 'Bind native function'
order: 60
---
In `VM` class, there are 4 methods to bind native function.
+ `VM::bind_func<ARGC>`
+ `VM::bind_builtin_func<ARGC>`
+ `VM::bind_method<ARGC>`
+ `VM::bind_static_method<ARGC>`
They are all template methods, the template argument is a `int` number, indicating the argument count. For variadic arguments, use `-1`. For methods, `ARGC` do not include `self`.
!!!
Native functions do not support keyword arguments.
!!!
PkPy uses a universal C function pointer for native functions:
```cpp
typedef PyObject* (*NativeFuncC)(VM*, ArgsView);
```
The first argument is the pointer of `VM` instance.
The second argument is a view of an array. You can use `[]` operator to get the element. If you have specified `ARGC` other than `-1`, the interpreter will ensure `args.size() == ARGC`. No need to do size check.
The return value is a `PyObject*`, which should not be `nullptr`. If there is no return value, return `vm->None`.
This is an example of binding the `input()` function to the `builtins` module.
```cpp
VM* vm = pkpy_new_vm(true);
vm->bind_builtin_func<0>("input", [](VM* vm, ArgsView args){
static std::string line;
std::getline(std::cin, line);
return VAR(line);
});
// vvv function name
vm->bind_builtin_func<2>("add", [](VM* vm, ArgsView args){
// ^ argument count
i64 lhs = CAST(i64, args[0]);
i64 rhs = CAST(i64, args[1]);
return VAR(lhs + rhs);
});
```

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---
icon: code
label: 'Wrap a native struct'
order: 50
---
Wrapping a `struct` as `PyObject`