python生产环境禁用assert断言的方法

1. 背景

在潜意识中, assert 是应用在unittest或pytest环境中, 不能应用到业务代码中, 因为断言会导致运行中断,对业务有损,并且消耗内存, 影响性能.

但不可否认, 使用断言非常方便调试代码

通过研读assert的文档, 发现断言是可以被关闭的,特此记录下

详细的介绍参考这个文档: 参考这篇文档

2.解决方案

2.1 禁用assert的策略

有两种方案

1. 启动命令行的参数中,添加-O, 也就是大写的o
2. 设置PYTHONOPTIMIZE环境变量为合适的值

2.2 禁用的原理

在python 内部机制中, 有一常量__debug__,值为BOOL类型的, 与断言是强关联的, 因为__debug__是常量, 所以当python 解释器运行时, 不能修改它的值.

Python 3.8.13 (default, Mar 28 2022, 06:16:26) 
[Clang 12.0.0 ] :: Anaconda, Inc. on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> __debug__
True
>>> __debug__ = False
  File "<stdin>", line 1
SyntaxError: cannot assign to __debug__
>>> 

既然运行时不能修改, 那没有运行时可以修改吗?当然可以的, 这取决于python 运行模式,python运行模式有两种,和__debug__的关系如下表所示:

那__debug__的值和断言有什么关系呢?

看源码:

if __debug__:
    if not expression:
        raise AssertionError(assertion_message)

所以__debug__==True时会抛出断言异常, __debug__==False时就啥也不干,跳过了

这下清晰了

3. 实施禁用策略

3.1 启动命令行的参数中,添加-O

验证方案:

1、先写这样一个测试脚本,命名为demo.py

# demo.py
print(f"__debug__=={__debug__}"

2、在命令行使用 禁用断言的启动方式

python -O demo.py

输出结果

__debug__==False

辅助理解: 在命令行中运行python -h,其结果也体现了这样的使用方式

mac$ python -h
usage: python [option] ... [-c cmd | -m mod | file | -] [arg] ...
Options and arguments (and corresponding environment variables):
-b     : issue warnings about str(bytes_instance), str(bytearray_instance)
         and comparing bytes/bytearray with str. (-bb: issue errors)
-B     : don't write .pyc files on import; also PYTHONDONTWRITEBYTECODE=x
-c cmd : program passed in as string (terminates option list)
-d     : debug output from parser; also PYTHONDEBUG=x
-E     : ignore PYTHON* environment variables (such as PYTHONPATH)
-h     : print this help message and exit (also --help)
-i     : inspect interactively after running script; forces a prompt even
         if stdin does not appear to be a terminal; also PYTHONINSPECT=x
-I     : isolate Python from the user's environment (implies -E and -s)
-m mod : run library module as a script (terminates option list)
-O     : remove assert and __debug__-dependent statements; add .opt-1 before
         .pyc extension; also PYTHONOPTIMIZE=x
-OO    : do -O changes and also discard docstrings; add .opt-2 before
         .pyc extension
-q     : don't print version and copyright messages on interactive startup
-s     : don't add user site directory to sys.path; also PYTHONNOUSERSITE
-S     : don't imply 'import site' on initialization
-u     : force the stdout and stderr streams to be unbuffered;
         this option has no effect on stdin; also PYTHONUNBUFFERED=x
-v     : verbose (trace import statements); also PYTHONVERBOSE=x
         can be supplied multiple times to increase verbosity
-V     : print the Python version number and exit (also --version)
         when given twice, print more information about the build
-W arg : warning control; arg is action:message:category:module:lineno
         also PYTHONWARNINGS=arg
-x     : skip first line of source, allowing use of non-Unix forms of #!cmd
-X opt : set implementation-specific option. The following options are available:

         -X faulthandler: enable faulthandler
         -X showrefcount: output the total reference count and number of used
             memory blocks when the program finishes or after each statement in the
             interactive interpreter. This only works on debug builds
         -X tracemalloc: start tracing Python memory allocations using the
             tracemalloc module. By default, only the most recent frame is stored in a
             traceback of a trace. Use -X tracemalloc=NFRAME to start tracing with a
             traceback limit of NFRAME frames
         -X showalloccount: output the total count of allocated objects for each
             type when the program finishes. This only works when Python was built with
             COUNT_ALLOCS defined
         -X importtime: show how long each import takes. It shows module name,
             cumulative time (including nested imports) and self time (excluding
             nested imports). Note that its output may be broken in multi-threaded
             application. Typical usage is python3 -X importtime -c 'import asyncio'
         -X dev: enable CPython's "development mode", introducing additional runtime
             checks which are too expensive to be enabled by default. Effect of the
             developer mode:
                * Add default warning filter, as -W default
                * Install debug hooks on memory allocators: see the PyMem_SetupDebugHooks() C function
                * Enable the faulthandler module to dump the Python traceback on a crash
                * Enable asyncio debug mode
                * Set the dev_mode attribute of sys.flags to True
                * io.IOBase destructor logs close() exceptions
         -X utf8: enable UTF-8 mode for operating system interfaces, overriding the default
             locale-aware mode. -X utf8=0 explicitly disables UTF-8 mode (even when it would
             otherwise activate automatically)
         -X pycache_prefix=PATH: enable writing .pyc files to a parallel tree rooted at the
             given directory instead of to the code tree

--check-hash-based-pycs always|default|never:
    control how Python invalidates hash-based .pyc files
file   : program read from script file
-      : program read from stdin (default; interactive mode if a tty)
arg ...: arguments passed to program in sys.argv[1:]

Other environment variables:
PYTHONSTARTUP: file executed on interactive startup (no default)
PYTHONPATH   : ':'-separated list of directories prefixed to the
               default module search path.  The result is sys.path.
PYTHONHOME   : alternate <prefix> directory (or <prefix>:<exec_prefix>).
               The default module search path uses <prefix>/lib/pythonX.X.
PYTHONCASEOK : ignore case in 'import' statements (Windows).
PYTHONUTF8: if set to 1, enable the UTF-8 mode.
PYTHONIOENCODING: Encoding[:errors] used for stdin/stdout/stderr.
PYTHONFAULTHANDLER: dump the Python traceback on fatal errors.
PYTHONHASHSEED: if this variable is set to 'random', a random value is used
   to seed the hashes of str and bytes objects.  It can also be set to an
   integer in the range [0,4294967295] to get hash values with a
   predictable seed.
PYTHONMALLOC: set the Python memory allocators and/or install debug hooks
   on Python memory allocators. Use PYTHONMALLOC=debug to install debug
   hooks.
PYTHONCOERCECLOCALE: if this variable is set to 0, it disables the locale
   coercion behavior. Use PYTHONCOERCECLOCALE=warn to request display of
   locale coercion and locale compatibility warnings on stderr.
PYTHONBREAKPOINT: if this variable is set to 0, it disables the default
   debugger. It can be set to the callable of your debugger of choice.
PYTHONDEVMODE: enable the development mode.
PYTHONPYCACHEPREFIX: root directory for bytecode cache (pyc) files.

5: 新的需求: 怎么在命令行中禁用断言,看下面的对比代码:

最关键是修改__debug__的值

(sse38) lzh mac$ python
Python 3.8.13 (default, Mar 28 2022, 06:16:26) 
[Clang 12.0.0 ] :: Anaconda, Inc. on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> __debug__
True
>>> exit()
(sse38) lzh mac$ python -O
Python 3.8.13 (default, Mar 28 2022, 06:16:26) 
[Clang 12.0.0 ] :: Anaconda, Inc. on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> __debug__
False
>>> 

3.2 设置PYTHONOPTIMIZE环境变量

这部分是在命令行中操作的

mac or linux 系统中,

(sse38)  mac$ export PYTHONOPTIMIZE=0
(sse38)  mac$ python demo.py
True
(sse38)  mac$ export PYTHONOPTIMIZE=1
(sse38)  mac$ python demo.py
False
(sse38)  mac$ export PYTHONOPTIMIZE=2
(sse38)  mac$ python demo.py
False

window 系统中,

(sse38)  mac$ set PYTHONOPTIMIZE=0
(sse38)  mac$ python demo.py
True
(sse38)  mac$ set PYTHONOPTIMIZE=1
(sse38)  mac$ python demo.py
False
(sse38)  mac$ set PYTHONOPTIMIZE=2
(sse38)  mac$ python demo.py
False

4 使用断言的坑

处理或验证数据

处理异常和异常

运行常有副作用的操作

到此这篇关于python生产环境禁用assert断言的文章就介绍到这了,更多相关python禁用assert断言内容请搜索猪先飞以前的文章或继续浏览下面的相关文章希望大家以后多多支持猪先飞！