Python中的asrt⽤法
Python中的asrt⽤法
本⽂转载⾃，如有侵权，⽴马删除！
中日词典使⽤asrt断⾔是学习Python⼀个⾮常好的习惯，Python asrt 断⾔ 语句格式及⽤法很简单；在没完善⼀个程序之前，我们不知道程序在哪⾥会出错，与其让它在运⾏时崩溃，不如在出现错误条件时就崩溃，这时候就需要asrt断⾔的帮助；本⽂主要是将asrt断⾔的基础知识。
Python asrt 断⾔的作⽤
tconPython asrt 断⾔是声明其布尔值必须为真的判定，如果发⽣异常就说明表达式为假。可以理解 asrt断⾔语句为rai-if-not，⽤来测试表达式，其返回值为假，就会触发异常。
asrt 断⾔语句的语法格式
asrt Python怎么⽤？
expression asrt 表达式
下⾯做⼀些asrt⽤法的语句供参考：
asrt1==1
asrt2+2==2*2
asrt len(['my boy',12])<10
asrt range(4)==[0,1,2,3]
如何为asrt断⾔语句添加异常参数
asrt的异常参数，其实就是在断⾔表达式后添加字符串信息，⽤来解释断⾔并更好的知道是哪⾥出了问题。格式如下：
asrt expression[,arguments]
asrt表达式[，参数]
picket fences
asrt len(lists)>=5,'列表元素个数⼩于5'
asrt2==1,'2不等于1'
Python asrt 为何不尽如⼈意
Python中的断⾔⽤起来⾮常简单，你可以在asrt后⾯跟上⼈意判断条件，如果断⾔失败则会抛出异常。
asrt 1+1 == 2
asrt isinstance('Hello', str)
asrt isinstance('Hello', int)
Traceback (most recent call last):
File "<stdin>", line 1, in<module>
AsrtionError
其实asrt看上去不错，然⽽⽤起来并不友好；就⽐如有⼈告诉你程序错了，但是不告诉哪⾥错了；很多时候这样的asrt还不如不写；直接抛⼀个异常会更好⼀些。
改进⽅案 #1
s ='nothin is impossible.'
key ='nothing'
asrt key in s, "key: '{}' is not in Target: '{}'".format(key, s)
Traceback (most recent call last):
File "<stdin>", line 1, in<module>
AsrtionError: key: 'nothing' is not int Target: 'nothin is impossible.'scalar
看上去还⾏，但是其实很是有点不友好；假如你是⼀名测试员，有成千上万的测试案例需要做断⾔做验证，这样的做法就不适⽤了。
改进⽅案 #2
不管你是做测试还是开发的，想必听过不少测试框架；
import pytest
def test_ca():
expected ='Hello'
actual ='hello'
asrt expected == actual
if __name__ =='__main__':
幼儿英语教学视频pytest.main()
执⾏结果如下：
=============================test ssion starts =============================
platform win32 -- Python 3.7.1, pytest-4.4.1, py-1.8.0, pluggy-0.9.0
rootdir: E:\Python5\newmallpro\TestAPI
however
collected 0 items / 1 errors
=================================== ERRORS ====================================
________________________ ERROR collecting test_one.py _________________________
ImportError while importing test module 'E:\Python5\newmallpro\TestAPI\test_one.py'.
Hint: make sure your test modules/packages have valid Python names.
Traceback:
test_one.py:10: in<module>
import requests
E ModuleNotFoundError: No module named 'requests'
Interrupted: 1 errors during collection
=========================== 1 error in 0.14 conds ===========================
unittest(单元测试)
Python⾃带的unittest单元测试框架就有了⾃⼰的断⾔⽅法lf.asrtXXX()，⽽且不推荐使⽤asrt XXX语句。
import unittest
class TestStringMethods(unittest.TestCa):
def test_upper(lf):
lf.asrtEqual('foo'.upper(),'FoO')
if __name__ =='__main__':
unittest.main()
执⾏结果如下：
FoO != FOO
Expected :FOO
Actual :FoO
<Click to e difference>
Traceback (most recent call last):pasrby是什么意思啊
File "D:\appinstallation\pycharminstall\PyCharm 2018.3.1\helpers\pycharm\teamcity\diff_tools.py", line 32, in _patched_equals
old(lf, first, cond, msg)
File "D:\appinstallation\pythonInstall\lib\unittest\ca.py", line 839, in asrtEqual
asrtion_func(first, cond, msg=msg)
File "D:\appinstallation\pythonInstall\lib\unittest\ca.py", line 1220, in asrtMultiLineEqual
lf.fail(lf._formatMessage(msg, standardMsg))
File "D:\appinstallation\pythonInstall\lib\unittest\ca.py", line 680, in fail
rai lf.failureException(msg)
AsrtionError: 'FOO'!='FoO'
ptest
ptest中的断⾔可读性很好，⽽且智能提⽰也很⽅便你通过IDE轻松完成各种断⾔语句。感谢Karl⼤神写了这个⼀个测试框架。
from ptest.decorator import*
from ptest.asrtion import*
@TestClass()
class TestCas:
暗黄皮肤如何美白
@Test()
新文道def test1(lf):
actual ='foo'
expected ='bar'
asrt_that(expected).is_equal_to(actual)
if __name__ =='__main__':
TestCas().test1()
执⾏结果如下：
AsrtionError: Unexpectedly that the str <bar> is not equal to str <foo>.
改进⽅案 #3
很多⼈对Python中的断⾔表⽰不满⾜，所以⼤家都争相发明⾃⼰的asrt包。在这⾥我强烈推荐asrtpy这个包，
它异常强⼤⽽且好评如潮。
pip install asrtpy
代码⽰例：
from asrtpy import asrt_that
def test_something():
asrt_that(1+2).is_equal_to(3)
asrt_that('foobar').is_length(6).starts_with('foo').ends_with('bar')
asrt_that(['a','b','c']).contains('a').does_not_contain('x')
asrt_that('a').is_length(4)
if __name__ =='__main__':
test_something()
执⾏结果如下：
AsrtionError: Expected <a> to be of length <4>, but was <1>.
从他的⽂档上你会发现它⽀持了⼏乎你能想到的所有所有测试场景，包括但不限于⼀下列表：
Strings
Numbers
Lists
Tuples
Dicts
Sets在线汉英互译
Booleans
Dates
Fiels
Objects
⽽且它的断⾔信息简洁明了，不多不少。
Expected <foo> to be of length <4>, but was <3>.
Expected <foo> to be empty string, but was not.
Expected <Fal>, but was not.
Expected <foo> to contain only digits, but did not.
Expected <123> to contain only alphabetic chars, but did not.
Expected <foo> to contain only upperca chars, but did not.
Expected <FOO> to contain only lowerca chars, but did not.
Expected <foo> to be equal to <bar>, but was not.
Expected <foo> to be not equal to <foo>, but was.
Expected <foo> to be ca-innsitive equal to <BAR>, but was not.
总结
断⾔在软件中有⾮常重要的作⽤，写的好可以让你的系统更稳定，也可以让你有更多真正⾯对对象的时间，⽽不是在调试代码。
Python中默认的断⾔语句其实还有⼀个作⽤，如果你写了⼀个类型相关的断⾔，IDE会把这个对象当成这种类型，这时候智能提⽰就有如神助。
要不要把内置的断⾔语句换成可读性更好功能更强⼤的第三⽅断⾔，完全取决于实际情况。⽐如你真的需要验证某个东西并且很关⼼验证结果，那么必须不能⽤简单的asrt；如果你只是担⼼某个点可能有坑或者让IDE认识某个对象，⽤内置的asrt既简单⼜⽅便。
本⽂转载⾃，如有侵权，⽴马删除！
