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异常处理
内容： 在编程时，错误是不可避免的事实。也许用户提供了错误的输入，也许网络资源不可用，也许程序内存不足。或者，程序员可能甚至犯了一个错误！
Python 对错误的解决方案是异常。你可能以前见过异常。
print(a)
# 错误
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
NameError: name 'a' is not defined
哎呀！忘记给变量 'a' 赋值了。
但有时你不希望异常完全停止程序。你可能想在引发异常时做一些特殊的事情。这可以在 try/except 块中完成。
这是一个简单的例子：假设你在迭代一个列表。你需要迭代 20 个数字，但这个列表是由用户输入生成的，可能没有 20 个数字。当你到达列表的末尾时，你只是希望剩下的数字被解释为 0。你可以这样做：
def do_stuff_with_number(n):
print(n)
def catch_this():
the_list = (1, 2, 3, 4, 5)
for i in range(20):
try:
do_stuff_with_number(the_list[i])
except IndexError: # 当访问列表中不存在的索引时引发
do_stuff_with_number(0)
catch_this()
看，这并不难！你可以用任何异常做到这一点。想了解更多关于处理异常的细节，请查看 Python 文档。
练习
处理所有的异常！回想之前的课程以返回演员的姓氏。
# Setup
actor = {"name": "John Cleese", "rank": "awesome"}
# Function to modify!!!
def get_last_name():
return actor["last_name"]
# Test code
get_last_name()
print("All exceptions caught! Good job!")
print("The actor's last name is %s" % get_last_name())
actor = {"name": "John Cleese", "rank": "awesome"}
def get_last_name():
return actor["name"].split()[1]
get_last_name()
print("All exceptions caught! Good job!")
print("The actor's last name is %s" % get_last_name())
test_output_contains("Cleese")
test_output_contains("All exceptions caught! Good job!")
test_output_contains("The actor's last name is Cleese")
success_msg("Great work!")
This site is generously supported by DataCamp. DataCamp offers online interactive Python Tutorials for Data Science. Join over a million other learners and get started learning Python for data science today!
