python3 learning exception handling and various file operations

This article mainly talks about the exception handling of Python3 and various file operations. It has a certain collection value. Interested friends can learn about it. I hope it will be helpful to you.

Exception handling: It is to prevent the program from terminating due to a small problem

try:

Code blocks where exceptions may occur

except:

Exception handling method

else:

Code to be executed when there is no error

If an exception occurs in the function, it will be executed normally after processing , if not handled, the exception will be thrown to the calling site and processed at the calling site. If it reaches the global scope and is not handled, an exception will occur and the program will terminate.

After an exception occurs, all exception information will be saved in a In a special exception object, when the exception is propagated, the exception object is actually thrown to the calling site.

If there is no exception type after except, all exceptions will be captured. If a fixed exception type is written, only To capture this type of exception, multiple excepts can be written to capture multiple different exceptions at the same time. The last except is usually written except Exception: capture all exceptions

except Exception as variable name: assign the captured exception object to A certain variable

can be followed by a finally: statement: No matter whether there is an exception or not, the finally statement will be executed.

try is necessary, else can be present or not, there must be at least one except and finally

raise is used to throw an exception to the outside, which can be followed by an exception class, or an instance of the exception class

raise Exception throws an exception

raise Exception('error string ') throws an exception and prompts

Custom exception:

class class name (exception type):

Code block

Throws a custom exception :

raise custom exception class name

io stream:

open(file path) Open the file and return the file object

with...as Statement:

with open(file_path) as file:

content = file.read()

print(content)

read() can receive A size parameter is used to specify the number of characters to be read. The default value is -1. It will read all characters in the file.

File object.readline() method, read at one time One line

File object.readline(read content,end='') No line break after reading one line

File object.readlines() is used to read line by line, one time Encapsulate the read content into a list and return it

open opens a file, and the file can be divided into two types

1. Plain text file, written using encoding such as utf-8 Text document

2. Binary files (pictures, mp3, ppt, etc.)

openWhen opening a file, it is opened as a text file by default, but the default encoding of open is None. Specify encoding:

with open(path,encoding='code table') as file

File writing:

write() method writes content to the file, If you are operating a text file, write() needs to pass a string as a parameter. After the writing is completed, the number of characters written will be returned.

When using open to open a file, you must specify the open file The required operations (read, write, append), if the operation type is not specified, the default is to read the file:

r means read-only

w means writable, use w to When writing a file, if the file does not exist, the file will be created. If it exists, the original content will be deleted. Writing new content

a means appending content. If the file does not exist, the file will be created. If it exists, the file will be added to the file. Append content

r Readable and writable, the file does not exist and error message

w Readable and writable, the file does not exist and created

a Readable and writable, the file does not exist and created

x Create a new file. If the file does not exist, create it. If the file exists, an error will be reported.

t Read text file (default value)

b Read binary text

rb Read binary text

When reading text, size is in characters.

When reading binary files, size is in bytes.

Object name.tell () Current reading position

Object name.seek (start reading position) Modify the current reading position

seek two parameters:

1. Required Switch to the position

2. Calculate the position method

Optional values:

0. Calculate from scratch, default value

1.Calculate from the current position

2. Calculate from the last position

Chinese: three bytes = 1 character

os module:

os.listdir() Get Current directory list

os.getcwd() Get the current directory

os.chdir(directory) Switch directory

os.mkdir(directory name) Create directory

os.rmdir(directory name) Delete directory

os.remove('file name') Delete file

os.rename('old name','new name') Rename You can also cut files by naming them

Related tutorials:Python3 video tutorial

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