Hướng dẫn write append file python

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While reading or writing to a file, access mode governs the type of operations possible in the opened file. It refers to how the file will be used once it’s opened. These modes also define the location of the File Handle in the file. The definition of these access modes is as follows:

• Append Only (‘a’): Open the file for writing.
• Append and Read (‘a+’): Open the file for reading and writing.

When the file is opened in append mode in Python, the handle is positioned at the end of the file. The data being written will be inserted at the end, after the existing data. 

Example 1: Python program to illustrate Append vs write mode.

Python3

file1 = open("myfile.txt", "w")

L = ["This is Delhi \n", "This is Paris \n", "This is London"]

file1.writelines(L)

file1.close()

file1 = open("myfile.txt", "a") 

file1.write("Today \n")

file1.close()

file1 = open("myfile.txt", "r")

print("Output of Readlines after appending")

print(file1.read())

print()

file1.close()

file1 = open("myfile.txt", "w") 

file1.write("Tomorrow \n")

file1.close()

file1 = open("myfile.txt", "r")

print("Output of Readlines after writing")

print(file1.read())

print()

file1.close()

Output:

Output of Readlines after appending
This is Delhi
This is Paris
This is LondonToday


Output of Readlines after writing
Tomorrow

Example 2:  Append data from a new line

In the above example of file handling, it can be seen that the data is not appended from the new line. This can be done by writing the newline ‘\n’ character to the file. 

Python3

file1 = open("myfile.txt", "w")

L = ["This is Delhi \n", "This is Paris \n", "This is London"]

file1.writelines(L)

file1.close()

file1 = open("myfile.txt", "a")

file1.write("\n")

file1.write("Today")

file1.write("Tomorrow")

file1 = open("myfile.txt", "r")

print("Output of Readlines after appending")

print(file1.read())

print()

file1.close()

Output:

Output of Readlines after appending
This is Delhi
This is Paris
This is London
TodayTomorrow

Note: ‘\n’ is treated as a special character of two bytes.

Example 3:  Using With statement  in Python

with statement is used in exception handling to make the code cleaner and much more readable. It simplifies the management of common resources like file streams. Unlike the above implementations, there is no need to call file.close() when using with statement. The with statement itself ensures proper acquisition and release of resources. 

Python3

L = ["This is Delhi \n", "This is Paris \n", "This is London \n"]

with open("myfile.txt", "w") as file1:

    file1.write("Hello \n")

    file1.writelines(L)

with open("myfile.txt", 'a') as file1:

    file1.write("Today")

with open("myfile.txt", "r+") as file1:

    print(file1.read())

Output:

Hello
This is Delhi
This is Paris
This is London
Today

Note: To know more about with statement click here.