Python错误处理机制

@(python程序员)[Python]

Python Cookbook

捕获所有的异常

处理异常的时候最好还会尽可能地使用精确的异常类。

def parse_int(s):
    try:
        n = int(v)
    except Exception as e:
        print("Couldn't parse")
        print("Reason:",e)

parse_int('42')
#Couldn't parse
#Reason: name 'v' is not defined

Learning Python

Exception Basics

Suppose we write the following function:

def fetcher(obj, index):
    return obj[index]

x = 'spam'
fetcher(x, 3)
#'m'

Catching Exceptions

def catcher():
    try:
        fetcher(x, 4)
    except IndexError:
        print('got exception')
    print('continuing')

catcher()
#got exception
#continuing

Raising Exceptions

try:
    raise IndexError # Trigger exception manually
except IndexError:
    print('got exception')

Exception Coding Details

try/except
Catch and recover from exceptions raised by Python, or by you.
try/finally
Perform cleanup actions, whether exceptions occur or not.
raise
Trigger an exception manually in your code.
assert
Conditionally trigger an exception in your code.
with/as
Implement context managers in Python 2.6, 3.0, and later (optional in 2.5).

The try/except/else Statement

try:
    statements # Run this main action first
except name1:
    statements # Run if name1 is raised during try block
except (name2, name3):
    statements # Run if any of these exceptions occur
except name4 as var:
    statements # Run if name4 is raised, assign instance raised to var
except:
    statements # Run for all other exceptions raised
else:
    statements # Run if no exception was raised during try block

with/as Context Managers

The basic format of the with statement looks like this

with expression [as variable]:
    with-block

Pro Python Best Practices

Exceptions in Python

The Error Type

Technically, an error message means that Python has raised an Exception. The error type indicates which Exception class was raised. All Exceptions are subclasses of the Exception class. In Python 3.5, there is a total of 47 different Exception types. You can see the full list of Exceptions with

所有的Exceptions都是Exception类的子类。在Python3.5中一共有47中Exception类型。

[x for x in dir(__builtins__) if 'Error' in x]

Figure: Hierarchy of Python Exceptions