Files
flatbuffers/tests/MyGame/Example/NestedStruct.py
Łukasz Kurowski c526cb640b [Python] Enhance object API __init__ with typed keyword arguments (#8615)
This commit significantly improves the developer experience for the Python Object-Based API by overhauling the generated `__init__` method for `T`-suffixed classes.

Previously, `T` objects had to be instantiated with an empty constructor, and their fields had to be populated manually one by one. This was verbose and not idiomatic Python.

This change modifies the Python code generator (`GenInitialize`) to produce `__init__` methods that are:

1.  **Keyword-Argument-Friendly**: The constructor now accepts all table/struct fields as keyword arguments, allowing for concise, single-line object creation.

2.  **Fully Typed**: The signature of the `__init__` method is now annotated with Python type hints. This provides immediate benefits for static analysis tools (like Mypy) and IDEs, enabling better autocompletion and type checking.

3.  **Correctly Optional**: The generator now correctly wraps types in `Optional[...]` if their default value is `None`. This applies to strings, vectors, and other nullable fields, ensuring strict type safety.

The new approach remains **fully backward-compatible**, as all arguments have default values. Existing code that uses the empty constructor will continue to work without modification.

#### Example of a Generated `__init__`

**Before:**

```python
class KeyValueT(object):
    def __init__(self):
        self.key = None  # type: str
        self.value = None  # type: str
```

**After:**

```python
class KeyValueT(object):
    def __init__(self, key: Optional[str] = None, value: Optional[str] = None):
        self.key = key
        self.value = value
```

#### Example of User Code

**Before:**

```python
# Old, verbose way
kv = KeyValueT()
kv.key = "instrument"
kv.value = "EUR/USD"
```

**After:**

```python
# New, Pythonic way
kv = KeyValueT(key="instrument", value="EUR/USD")
```
2025-07-22 23:57:39 -07:00

166 lines
5.1 KiB
Python

# automatically generated by the FlatBuffers compiler, do not modify
# namespace: Example
import flatbuffers
from flatbuffers.compat import import_numpy
from typing import Any
np = import_numpy()
class NestedStruct(object):
__slots__ = ['_tab']
@classmethod
def SizeOf(cls) -> int:
return 32
# NestedStruct
def Init(self, buf: bytes, pos: int):
self._tab = flatbuffers.table.Table(buf, pos)
# NestedStruct
def A(self, j = None):
if j is None:
return [self._tab.Get(flatbuffers.number_types.Int32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(0 + i * 4)) for i in range(self.ALength())]
elif j >= 0 and j < self.ALength():
return self._tab.Get(flatbuffers.number_types.Int32Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(0 + j * 4))
else:
return None
# NestedStruct
def AAsNumpy(self):
return self._tab.GetArrayAsNumpy(flatbuffers.number_types.Int32Flags, self._tab.Pos + 0, self.ALength())
# NestedStruct
def ALength(self) -> int:
return 2
# NestedStruct
def AIsNone(self) -> bool:
return False
# NestedStruct
def B(self): return self._tab.Get(flatbuffers.number_types.Int8Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(8))
# NestedStruct
def C(self, j = None):
if j is None:
return [self._tab.Get(flatbuffers.number_types.Int8Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(9 + i * 1)) for i in range(self.CLength())]
elif j >= 0 and j < self.CLength():
return self._tab.Get(flatbuffers.number_types.Int8Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(9 + j * 1))
else:
return None
# NestedStruct
def CAsNumpy(self):
return self._tab.GetArrayAsNumpy(flatbuffers.number_types.Int8Flags, self._tab.Pos + 9, self.CLength())
# NestedStruct
def CLength(self) -> int:
return 2
# NestedStruct
def CIsNone(self) -> bool:
return False
# NestedStruct
def D(self, j = None):
if j is None:
return [self._tab.Get(flatbuffers.number_types.Int64Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(16 + i * 8)) for i in range(self.DLength())]
elif j >= 0 and j < self.DLength():
return self._tab.Get(flatbuffers.number_types.Int64Flags, self._tab.Pos + flatbuffers.number_types.UOffsetTFlags.py_type(16 + j * 8))
else:
return None
# NestedStruct
def DAsNumpy(self):
return self._tab.GetArrayAsNumpy(flatbuffers.number_types.Int64Flags, self._tab.Pos + 16, self.DLength())
# NestedStruct
def DLength(self) -> int:
return 2
# NestedStruct
def DIsNone(self) -> bool:
return False
def CreateNestedStruct(builder, a, b, c, d):
builder.Prep(8, 32)
for _idx0 in range(2 , 0, -1):
builder.PrependInt64(d[_idx0-1])
builder.Pad(5)
for _idx0 in range(2 , 0, -1):
builder.PrependInt8(c[_idx0-1])
builder.PrependInt8(b)
for _idx0 in range(2 , 0, -1):
builder.PrependInt32(a[_idx0-1])
return builder.Offset()
try:
from typing import List
except:
pass
class NestedStructT(object):
# NestedStructT
def __init__(
self,
a = None,
b = 0,
c = None,
d = None,
):
self.a = a # type: Optional[List[int]]
self.b = b # type: int
self.c = c # type: Optional[List[int]]
self.d = d # type: Optional[List[int]]
@classmethod
def InitFromBuf(cls, buf, pos):
nestedStruct = NestedStruct()
nestedStruct.Init(buf, pos)
return cls.InitFromObj(nestedStruct)
@classmethod
def InitFromPackedBuf(cls, buf, pos=0):
n = flatbuffers.encode.Get(flatbuffers.packer.uoffset, buf, pos)
return cls.InitFromBuf(buf, pos+n)
@classmethod
def InitFromObj(cls, nestedStruct):
x = NestedStructT()
x._UnPack(nestedStruct)
return x
# NestedStructT
def _UnPack(self, nestedStruct):
if nestedStruct is None:
return
if not nestedStruct.AIsNone():
if np is None:
self.a = []
for i in range(nestedStruct.ALength()):
self.a.append(nestedStruct.A(i))
else:
self.a = nestedStruct.AAsNumpy()
self.b = nestedStruct.B()
if not nestedStruct.CIsNone():
if np is None:
self.c = []
for i in range(nestedStruct.CLength()):
self.c.append(nestedStruct.C(i))
else:
self.c = nestedStruct.CAsNumpy()
if not nestedStruct.DIsNone():
if np is None:
self.d = []
for i in range(nestedStruct.DLength()):
self.d.append(nestedStruct.D(i))
else:
self.d = nestedStruct.DAsNumpy()
# NestedStructT
def Pack(self, builder):
return CreateNestedStruct(builder, self.a, self.b, self.c, self.d)