Exception catching method in python

To handle exceptions in Python, try-except code blocks are used. The try-except code blocks put the operations for python to perform, and at the same time tell the python program what to do if an exception occurs. There are actually many ways to get started with the try-except function. Books have put them in advanced chapters, and generally do not talk about its use when getting started. Especially as an operation and maintenance personnel, if you often write shells, you will probably rarely use this function after switching to python. I think this function explains An important difference between shell and python is that python is a real programming language. Other programming languages ​​​​such as php and java will provide exception catching functions. The code written using these programs must be robust. If you read Some program codes written by other people, especially some socket programming codes, many of them are try...except..., and some have multiple excepts to judge various situations. Since this function is so useful, let's do it Let’s learn how to use it as soon as possible.

First, let’s take a look at its syntax. The syntax is very simple, which is to put the code block you want to execute in try-except, for example:,

try:
  somecode1
except 异常类型/名称:
  somecode2

This is the simplest case. If the situation is complicated, you can use multiple except sentences, for example:

try:
  somecode0
except 异常类型/名称1:
  somecode1
except 异常2:
  somecode2
except 异常3:
  somecode3

## There are more advanced usages of #try-except, including else, finally, etc. We won’t go into details today. If you are interested, you can study it in depth yourself.

Next let’s look at a simple example. Our common operations are to read and write files. A common problem is that the file cannot be found, or the file name or path is incorrect. In this case, you can use The try-except code block is handled in an intuitive way:

try:
  withopen(filename, 'r+') as fp:
    data = fp.read()
exceptIOError:
  msg = 'sorry, can not read or write this ' + filename
  printmsg

Let’s look at another example of multiple excepts, subtracting two numbers:

loop = 1
while loop == 1:
  try:
    a = input('请输入第一个数字> ')
    b = input('请输入第二个数字 > ')
  exceptNameError:
    print "请输入数字，不能输入字母"
 continue
  exceptSyntaxError:
    print "请仅输入一个数字."
 continue
  print a - b
  try:
    loop = input('按1再开始 > ')
  except (NameError,SyntaxError):
    loop = 0

The above two examples are the simplest usage of try-except. If you want to ensure the robustness of the script, you can use try-except code blocks more in the future. This It will make your code look more professional.

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