异常与调试

通过try...except...finally处理异常。

try:
    print 'try...'
    r = 10 / 0
    print 'result:', r
except ValueError, e:
    print 'ValueError:', e
except ZeroDivisionError, e:
    print 'except:', e
finally:
    print 'finally...'
print 'END'

调用
try...
except: integer division or modulo by zero
finally...
END

调用堆栈

出现异常返回时，会打印调用堆栈

# err.py:
def foo(s):
    return 10 / int(s)

def bar(s):
    return foo(s) * 2

def main():
    bar('0')

main()

执行结果：
$ python err.py
Traceback (most recent call last):
  File "err.py", line 11, in 
    main()
  File "err.py", line 9, in main
    bar('0')
  File "err.py", line 6, in bar
    return foo(s) * 2
  File "err.py", line 3, in foo
    return 10 / int(s)
ZeroDivisionError: integer division or modulo by zero

记录错误

# err.py
import logging

def foo(s):
    return 10 / int(s)

def bar(s):
    return foo(s) * 2

def main():
    try:
        bar('0')
    except StandardError, e:
        logging.exception(e)

main()
print 'END'

抛出异常

# err.py
class FooError(StandardError):
    pass

def foo(s):
    n = int(s)
    if n==0:
        raise FooError('invalid value: %s' % s)
    return 10 / n

raise语句如果不带参数，就会把当前错误原样抛出

# err.py
def foo(s):
    n = int(s)
    return 10 / n

def bar(s):
    try:
        return foo(s) * 2
    except StandardError, e:
        print 'Error!'
        raise

def main():
    bar('0')

main()

调试

• print打印
• 断言 断言失败，assert语句本身就会抛出AssertionError：

# err.py
def foo(s):
    n = int(s)
    assert n != 0, 'n is zero!'
    return 10 / n

def main():
    foo('0')

启动Python解释器时可以用-O参数来关闭assert

• logging 打印日志
• 启动Python的调试器pdb，让程序以单步方式运行

python -m pdb err.py
pdb.set_trace() 设置断点
pycharm IDE也可以设置断点执行