Python 程序的语法是正确的，在运行它的时候，也有可能发生错误。运行期检测到的错误被称为异常。
一、异常处理
1. try...except....
"""1. try...except....""" try: a = 3/0 except BaseException as e: print(e) print(type(e)) —————————————————————————————— division by zero <class 'ZeroDivisionError'>
2. try...except...except...except...
"""2. try...except...except...except...""" # 一个 try 语句可能包含多个except子句，分别来处理不同的特定的异常。最多只有一个分支会被执行
3. try...except....else
如果有异常执行except，没有异常执行else
"""3. try...except....else""" # 如果有异常执行except，没有异常执行else try: a = 3/2 except BaseException as e: print(e) else: print("无异常！") # 无异常！ ___________________________________________ 无异常！
4. try...except...else...finally...
finally块无论是否发生异常都会被执行，通常用来释放try块中的申请资源
"""4. try...except...else...finally...""" # finally块无论是否发生异常都会被执行，通常用来释放try块中的申请资源 try: f = open("/Users/chushujin/chushujin/myworkspsace/csjin-Test/mypythonscript","r") content = f.readline() print(content) except IOError as e: print(e) finally: pass
5. return语句一般不放在try...except...else...finally块中，建议放到最后
"""5. return语句一般不放在try...except...else...finally块中，建议放到最后""" def test001(): try: print("1") except Exception as e: print(e) finally: print("结束") return "1"
二、常见的异常
1. 语法错误:invalid syntax
# 6.1 语法错误:invalid syntax int a =3 —————————————————————————————————— File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test01.py", line 61 int a =3 ^ IndentationError: unexpected indent
2. 尝试访问一个没有申明的变量:NameError: name 'b' is not defined
# 6.2 尝试访问一个没有申明的变量:NameError: name 'b' is not defined print(b) —————————————————————————————— Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test01.py", line 66, in <module> print(b) NameError: name 'b' is not defined
3. 除数不能为0：ZeroDivisionError: division by zero
#6.3 除数不能为0：ZeroDivisionError: division by zero # a = 3/0 ——————————————————————————————————— Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test01.py", line 70, in <module> a = 3/0 ZeroDivisionError: division by zero
4. 数值错误：ValueError: could not convert string to float: '褚'
# 6.4 数值错误：ValueError: could not convert string to float: '褚' # float("褚") ———————————————————————————————— Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test01.py", line 73, in <module> float("褚") ValueError: could not convert string to float: '褚'
5. 类型错误：TypeError: unsupported operand type(s) for +: 'int' and 'str'
# 6.5 类型错误：TypeError: unsupported operand type(s) for +: 'int' and 'str' 123+"abc" —————————————————————————————————— Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test01.py", line 76, in <module> 123+"abc" TypeError: unsupported operand type(s) for +: 'int' and 'str'
6. 访问对象的不存在的属性:AttributeError: 'str' object has no attribute 'say'
# 6.6 访问对象的不存在的属性:AttributeError: 'str' object has no attribute 'say' a = "666" a.say() —————————————————————————————————— Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test01.py", line 80, in <module> a.say() AttributeError: 'str' object has no attribute 'say'
7. 索引越界异常:IndexError: string index out of range
# 6.7 索引越界异常:IndexError: string index out of range b = [1,2,3] a[10] —————————————————————————————————— Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test01.py", line 84, in <module> a[10] IndexError: string index out of range
8. 字段关键字不存在:KeyError: 'n'
# 6.8 字段关键字不存在:KeyError: 'n' d = {"name":"chu"} d['n'] —————————————————————————————————— Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test01.py", line 88, in <module> d['n'] KeyError: 'n'
三、使用with content_expr [as f]:自动关闭。无需手动关闭文件
import os path = os.path.split(os.path.split(os.path.realpath(__file__))[0])[0] # ('C:\chushujin\study\mypythonscript\src\com.csjin.qa2020\TestException', 'Test02.py') print(path) path_txt = os.path.join(path,"test.txt") """ with context_expr [as f]""" with open(path_txt,encoding="utf-8") as f: print(f.readline())
四、traceback模块使用
1. 打印详细信息
"""traceback使用""" import os path = os.path.split(os.path.split(os.path.realpath(__file__))[0])[0] # ('C:\chushujin\study\mypythonscript\src\com.csjin.qa2020\TestException', 'Test02.py') print(path) path_txt = os.path.join(path,"test.txt") import traceback try: a = 3/0 except: traceback.print_exc() —————————————————————————————————— """ Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test03.py", line 9, in <module> a = 3/0 ZeroDivisionError: division by zero """
2. 将异常写入文件
try: a = 3/0 except: # 将错误信息输入至文件 with open(path_txt,"a") as f: traceback.print_exc(file=f)
文件中展示为：
111111111111111111Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test03.py", line 32, in <module> a = 3/0 ZeroDivisionError: division by zero Traceback (most recent call last): File "C:/chushujin/study/mypythonscript/src/com.csjin.qa2020/TestException/Test03.py", line 32, in <module> a = 3/0 ZeroDivisionError: division by zero
五、自定义异常
Python 使用 raise 语句抛出一个指定的异常。
raise 唯一的一个参数指定了要被抛出的异常。它必须是一个异常的实例或者是异常的类（也就是 Exception 的子类）。
只想知道这是否抛出了一个异常，并不想去处理它，那么一个简单的 raise 语句就可以再次把它抛出。
"""自定义异常""" class AgeError(Exception): def __init__(self,errorInfo): Exception.__init__(self) self.errorInfo = errorInfo def __str__(self): return str(self.errorInfo)+"年龄错误" ############################################ if __name__ == '__main__': age = int(input("请输入一个数字：")) if age < 1 or age >150: raise AgeError(age) else: print("年龄正常") """ __main__.AgeError: 200年龄错误 """