Python 函数变量类型注释会导致用 Cython 编译后执行与直接执行结果不一致
最近工作中遇到关于函数类型注释引起的错误,特此记录一下。
起因是公司的项目为了安全和执行速度,在发布时会使用 Cython 转为 C 语言并编译成动态连接库进行调用,但是有个函数在 Python 执行时正常,但是在动态连接库中却执行错误。
错误复现
测试用例 test.py
:
def ip_str(ips: str): |
编译 compile.py
:
from setuptools import setup |
运行编译:
python compile.py build |
编译之后进入对应 so 文件目录 build/lib-{平台架构}
,运行对比:
>>> import test |
经过调查发现,当函数变量做了类型注释时,不能重新赋值为其他类型,否则会在 Cython 编译后执行时报错。
Cython 可以在编译时推断出部分简单的错误,比如:
def ip1(): |
Error compiling Cython file: |
但如果代码比较复杂,则只能在运行时才会出错。所以上述错误只能在执行的时候才被抛出。
原因
Cython 将 Python 转为 C 代码比较后类型注释与否代码比较:
-
没有类型注释:
/* "test.py":2
*
* def ip_str(ips: str): # <<<<<<<<<<<<<<
* ips = [x for x in ips]
*
*/
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/* "test.py":3
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*
* def ip(ips):
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有类型注释:
/* "test.py":2
*
* def ip_str(ips: str): # <<<<<<<<<<<<<<
* ips = [x for x in ips]
*
*/
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/* "test.py":5
* ips = [x for x in ips]
*
* def ip(ips): # <<<<<<<<<<<<<<
* ips = [x for x in ips]
*/
/* Python wrapper */
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主要区别在于,类型注释增加了变量检测 __Pyx_ArgTypeTest
,以及之后赋值 ips 时的类型检测 PyString_CheckExact
;没有变量类型注释则进行了变量推测,判断是否为List( PyList_CheckExact
)或者Tuple ( PyTuple_CheckExact
),还是可迭代类型。
结论
- 类型注释在编译后会简化处理流程;
- 类型注释的变量不能赋值为其他类型。
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