Python异常处理和程序调试

Table of Contents

1. Python中的异常

2. try...except使用

2.1 没有捕获

2.2 添加捕获

3. try...except...finally

4. raise抛出异常

5. 自定义异常

6. assert断言语句使用

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1. Python中的异常

2. try...except使用

2.1 没有捕获

#try:
    open("hello.txt")
#except FileNotFoundError:
    print("file not found")
#except:
    print("Program abort")

调试信息（程序异常退出）：

C:\Python\Python38\python.exe "E:/python/python project/hello world.py"
  File "E:/python/python project/hello world.py", line 4
    open("hello.txt")
    ^
IndentationError: unexpected indent

Process finished with exit code 1

2.2 添加捕获

try:
    open("hello.txt")
except FileNotFoundError:
    print("file not found")
except:
    print("Program abort")

try:
    result = 10/0
except ZeroDivisionError:
    print("0 is division error")
else:
    print("resule=%d" % result)

调试信息（程序捕获到信息并能够正常运行）：

C:\Python\Python38\python.exe "E:/python/python project/hello world.py"
file not found
0 is division error

3. try...except...finally

源码：

try:
    f = open("hello.txt", "r")
except FileNotFoundError:
    print("File not found")
except:
    print("Program abort")
finally:
    print("Exec finally, Close fd")
    f.close()

结果：

C:\Python\Python38\python.exe "E:/python/python project/hello world.py"
Traceback (most recent call last):
file not found
  File "E:/python/python project/hello world.py", line 25, in 
0 is division error
    f.close()
NameError: name 'f' is not defined
File not found
Exec finally, Close fd

Process finished with exit code 1

4. raise抛出异常

try:
    s = None
    if s is None:
        print("s is None")
        raise NameError
    print(len(s))

except TypeError:
    print("Null object is no length")

C:\Python\Python38\python.exe "E:/python/python project/hello world.py"
s is None
Traceback (most recent call last):
  File "E:/python/python project/hello world.py", line 7, in 
    raise NameError
NameError

Process finished with exit code 1

5. 自定义异常

结果：

6. assert断言语句使用

t = "hello"
assert len(t) > 1

t = "hello"
assert len(t) == 1

C:\Python\Python38\python.exe "E:/python/python project/hello world.py"
Traceback (most recent call last):
  File "E:/python/python project/hello world.py", line 7, in 
    assert len(t) == 1
AssertionError

Process finished with exit code 1