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Catalogue* 1. Demand
1. Demand
The user enters any file name in the current directory, and the program completes the backup function of the file.
The backup file name is xx [backup] suffix, for example: test [backup] txt.
2. Steps
- Receive the file name entered by the user.
- Plan backup file name.
- Write data to the backup file.
3. Code implementation
(1) Receive user input target file name
python
old\_name = input('Please enter the file name you want to back up:')
(2) Planning backup file name
2.1 extract the suffix of the target file.
2.2 file name of organization backup, suffix xx [backup].
python
# 2.1 extract the subscript of the suffix point of the file
index = old\_name.rfind('.')
# 2.2 organization new file name old file name + [backup] + suffix
new\_name = old\_name[:index] + '[backups]' + old\_name[index:]
(3) Backup file write data
3.1 open source files and backup files.
3.2 write the source file data into the backup file.
3.3 close the file.
python
# 3.1 opening files
old\_f = open(old\_name, 'rb')
new\_f = open(new\_name, 'wb')
# 3.2 write source file data into backup file
# If you are not sure about the target file size, cycle reading and writing,
# When the read data is gone, the loop is terminated
while True:
# Contents read in the original file each time
con = old\_f.read(1024)
# Indicates that the read is complete
if len(con) == 0:
# Terminate reading
break
# New file write read data
new\_f.write(con)
# 3.3 closing documents
old\_f.close()
new\_f.close()
(4) Think
If the user enters txt, this is an invalid file. How can the program change to limit that only valid file names can be backed up?
Answer: add condition judgment.
python
# The suffix can only be extracted if there is a file name
# Suffixes cannot be obtained here. Variables without suffixes are spliced
# Will report an error
if index > 0:
postfix = old\_name[index:]
(5) Complete coding
1) Traditional implementation
python
# 1. The user inputs the target file, such as sound txt. mp3
old\_name = input('Please enter the file name you want to back up:')
# 2. Name of planning backup file
# 2.1 extracting suffixes--
# Find the rightmost point in the name is the suffix point
# Find the rfind() method on the right
# Gets the suffix in the full file name Location of
index = old\_name.rfind('.')
# 4. Thinking: only valid files can be backed up txt
if index > 0:
# Extract the suffix. If it cannot be extracted here, an error will be reported when splicing the new file name later
postfix = old\_name[index:]
# 2.2 organization new name = original name + [backup] + suffix
# The original name is a molecular string in the string -- slice [start: end: step]
# new\_name = old\_name[:index] + '[backup]' + old\_name[index:]
new\_name = old\_name[:index] + '[backups]' + postfix
# 3. Write data to the backup file (the data is the same as the original file)
# 3.1 open original and backup files
old\_f = open(old\_name, 'rb')
new\_f = open(new\_name, 'wb')
# 3.2 original file reading and backup file writing
# If the size of the target file is not determined, the cycle is read and written. When the read data is not available, the cycle is terminated
while True:
# Contents read in the original file each time
con = old\_f.read(1024)
# Indicates that the read is complete
if len(con) == 0:
# Terminate reading
break
# New file write read data
new\_f.write(con)
# 3.3 closing documents
old\_f.close()
new\_f.close()
2) Actual work realization
python
# 1. The user inputs the target file, such as sound txt. mp3
old\_name = input('Please enter the file name you want to back up:')
# Gets the suffix in the full file name Location of
index = old\_name.rfind('.')
# 4. Only valid files can be backed up txt
if index > 0:
postfix = old\_name[index:]
# 3. Start backing up files
# Open original file
with open(old\_name , 'rb') as file\_obj:
# New organization name = original name + [backup] + suffix
new\_name = old\_name[:index] + '[backups]' + postfix
# Create and open a new file
with open(new\_name, 'wb') as new\_obj:
# Defines the size of each read
chunk = 1024 * 100
while True:
# Read data from existing objects
content = file\_obj.read(chunk)
# After reading the content, terminate the cycle
if not content:
break
# Write the read data to the new object
new\_obj.write(content)
The functions of the two methods are the same.
4. Another little exercise
Requirement: binary file reading (the implementation method is the same as above)
python
# Read mode
# Tread text file (default)
# b read binary files
file\_name = "hello.txt"
with open(file\_name , 'rb') as file\_obj:
# When reading a text file, size is in characters
# When reading binary files, size is in bytes
# print(file\_obj.read(100))
# Write out the read content
# Define a new file
new\_name = 'aa.txt'
with open(new\_name , 'wb') as new\_obj:
# Defines the size of each read
chunk = 1024 * 100
while True :
# Read data from existing objects
content = file\_obj.read(chunk)
# After reading the content, terminate the cycle
if not content :
break
# Write the read data to the new object
new\_obj.write(content)
Note: plain text files can also be read using binary methods.
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__EOF__
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