Exception, import package and file operation

● In program development , If the execution of some code cannot be determined to be correct , Can increase try( Try ) To catch exceptions

● The simplest syntax format to catch exceptions :

try： Code to try to execute

except: Wrong handling

●try Try , Write the code below to try , Code that is not sure whether it can execute normally

●except If not , Write the failed code below
 

try:
    #  Prompt for a number 
    num = int(input(" Please enter an integer :"))
except:
    print(" Please enter the correct number ：")

  Capture the error ： Catch exceptions according to the error type , Catch unknown error

#  Full catch exception 

try:
    num = int(input(" Please enter an integer :"))

    result = 8 / num
    print(result)
#  Catch exceptions according to the error type 
except ZeroDivisionError:
    print(" The denominator cannot be 0, Please re-enter ：")
# except ValueError:
#     print(" Denominator is not a number , Please re-enter ：")
#  Catch unknown error 
except Exception as result:
    print(" An unknown error occurred %s" % result)
else:
    #  Code that will be executed only when there are no exceptions 
    print(" The input form is correct ！")
finally:
    #  Code that will execute whether there is an exception or not 
    print(" Code that will execute whether there is an exception or not ")

Transitivity of exceptions

● In development , Exception capture can be added to the main function

● Other functions that are called in the main function , As long as there is an exception , Will be passed to the exception capture of the main function

● So you don't have to be in the code , Add a lot of exception catching , Keep the code clean
 

def demo1():
    return int(input(" Input integer ："))


def demo2():
    return demo1()


#  Take advantage of the transitivity of exceptions , Catch exception in main program 

try:

    print(demo2())
except Exception as result:
    print(" Unknown error %s" % result)

Throw an exception

def input_password():
    password = input(" Please input a password :")
    if len(password) >= 8:
        return password
    print(" Throw an exception ")
    #  Create exception object , You can use the error message string as an argument 
    ex = Exception(" Insufficient password length ")
    #  Throw an exception 
    raise ex


try:
    print(input_password())
except Exception as result:
    print(result)

from   ...import Local import

#  Global variables 
# hm_ Test module 1
title = " modular 1"


#  function 
def say_hello():
    print(" I am a %s " % title)


#  class 
class Dog(object):
    pass

￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥

title = " modular 2"


# hm_ Test module 2

def say_hello():
    print(" I am a %s " % title)


class Cat(object):
    pass


￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥￥

from hm_ Test module 1 import Dog
from hm_ Test module 2 import say_hello

say_hello()
wangcai = Dog()
print(wangcai)

If two modules , There is a function with the same name , Then the function of the post import module , The function imported first will be overwritten

● When developing import The code should be written at the top of the code , It's easier to detect conflicts in time

● Once a conflict is found , have access to as Keyword to give an alias to one of the tools
 

__name__ attribute
 

●__name__ Properties can do , The code of the test module is run only under test , When imported, it will not be executed !
 

●__name__ yes Python A built-in property of , Records a string
 

● If it is imported by other files ,__name__ Namely Module name

● If it is the program currently executing __name__ yes __main__

package

● A package is a special directory that contains multiple modules

● There is a special file in the directory init_ .py

● The package name is named in the same way as the variable name , Lowercase letters + mouth

benefits

● Use import The package name can import all modules in the package at one time

● To use the modules in the package externally , Need to be in init_ . py Specify the list of modules provided to the outside world

init.py

from . import send_passage
from . import receive_message





send_passage.py

def send(num):
    print(" Sending file ..%s"%num)





receive_message.py

def receive():
    return " This is from 100 The SMS "




hm_ Import package 

import hm_message

hm_message.send_passage.send("hello")
txt = hm_message.receive_message.receive()
print(txt)




 result ：

 Sending file ..hello
 This is from 100 The SMS 

Make module compressed package

1. establish setup.py

2. Building blocks

The basic operation of the file

Open file

read 、 Writing documents （ read ： Read the contents of the file into memory , Write ： Write the contents of memory to a file ）

Close file

open The function is responsible for opening the file , And return the file object

read/write/close All three methods need to be called through a file object  

open The first argument to the function is the name of the file to open ( File names are case sensitive ). If the file exists , Returns the file operation object  . If the file doesn't exist , It throws an exception  
read Method can read in and return all the contents of the file at once

close Method is responsible for closing the file  
If you forget to close the file , It will cause system resource consumption , And it will affect subsequent access to files · Be careful : After method execution , Will move the file pointer to the end of the file

#1  Open a file name （ You need to pay attention to case ）
file = open("README")


# 2, Read file contents 

text = file.read()
print(text)


# 3, close 
file.close()

open Function does not edit the access method , The default is read-only , Don't write  

  readline Method

You can read one line at a time , After method execution , Will move the file pointer to the next line , Ready to read again

# Open file 

file = open.("README")


while True:
 And real ：

# Read a line 
         text = file.readline()
# Judge whether the content is read 
         if not text:
             break


     # There is already at the end of each read line — individual ‘\’
         print( text, end="")

 First close file 

file.close( )

File replication

  Small file copy

Open an existing file , Read the complete content , And write to another file

#1, open 

file_read = open( "README")
file_write = open( "REAMDE[ Copy ]","w"")

#2． read 、 Write 

text = file_read.read()
file_write.write(text)

#3． close 

file_read.close()
file_write.close()

Big file replication

Open an existing file , Read line by line , And write to another file in sequence m

#1, open 

file_read = open( "README")
file_write = open( "REAMDE[ Copy ]","w"")

#2． read 、 Write 
while True:
     text = file_read.readline()
     if not text:
       break
     file_write.write(text)

#3． close 

file_read.close()
file_write.close()

file / Common directory management operations

Import OS modular

file = open(r"a.txt", "w", encoding='utf-8')
text = [" Cage osprey \n"," In the river of continent "]
# write() Write string to file ,,
# writelines Write a list of strings to a file , Do not add line breaks 
# file.write(text)
file.writelines(text)
file.close()

with keyword

Context resources can be managed automatically , Jump out for whatever reason with block , Can ensure that the file is closed correctly , And it can automatically restore the scene when entering the code block after the code block is executed .
 

​


file= ["123\n","456"]
with open(r"b.txt","w") as file1:
    file1.writelines(file)