Python Program to Remove Lines Starting with any Prefix

Files in Python:

One of the most important subjects for programmers and automation testers is Python file handling (also known as File I/O). It is necessary to work with files in order to write to or read data from them.

Also, if you didn’t know, I/O operations are the most expensive processes where a program can go wrong. As a result, you must use extreme caution while implementing file processing for reporting or any other reason. Optimizing a single file action can help in the creation of a high-performing application or a reliable automated software testing solution.

Consider the following scenario: you’re planning to construct a large Python project with a large number of workflows. Then it’s unavoidable that you don’t make a log file. You’ll also be handling the log file’s read and write activities. Debugging huge applications with log files is a terrific way to go. It’s usually better to consider a scalable design from the start, as you won’t be sorry later if you didn’t.

Given a file the task ist or remove lines starting with any given prefix and store them in new file in Python

Program to Remove Lines Starting with any Prefix in Python

Method #1: Using Built-in Functions

Approach:

Make a single variable to store the path of the file. This is a constant value. This value must be replaced with the file path from your own system in the example below.
Open the file in read-only mode. In this case, we’re simply reading the contents of the file.
Make another variable to store the path of the file. This is a constant value. This value must be replaced with the file path from your own system.
Open another file in write mode. In this case, we’re writing the contents into the file.
Give some random prefix as user input using the input() function and store it in a variable.
Iterate through the lines of the file using the for loop and readlines() function.
Check if the corresponding line starts with the given prefix using startswith() function and if conditional statement
If it is true then print the line.
Write the corresponding line to the writeFile using the write() function.
Close the above writing file using the close() function.
Close the above read file using the close() function.
The Exit of Program.

Below is the implementation:

# Make a single variable to store the path of the file. This is a constant value.
# This value must be replaced with the file path from your own system in the example below.
givenFilename = "samplefile.txt"
# Open the file in read-only mode. In this case, we're simply reading the contents of the file.
readFile = open(givenFilename, 'r')
# Make another variable to store the path of the file. This is a constant value.
# This value must be replaced with the file path from your own system.
writeFileName = "samplewritefile.txt"
# Open another file in write mode. In this case, we're writing the contents into the file.
writingFile = open(writeFileName,'w')
# Give some random prefix as user input using the input() function and store it in a variable
gvn_prefix = input("Enter some random prefix = ")
# Iterate through the lines of the file using the for loop and readlines() function
for lines in readFile .readlines(): 
    # Check if the corresponding line starts with the given prefix using startswith() function
    # and if conditional statement
    if not (lines.startswith(gvn_prefix)): 
        # If it is true then print the line
        print(lines)  
        # Write the corresponding line to the writeFile using the write() function
        writingFile.write(lines) 

# Close the above writing file using the close() function
writingFile.close() 
# Close the above read file using the close() function
readFile.close()

Output:

Enter some random prefix = hello
specific python codes Summary 
good morning this is btechgeeks 
welcome to btechgeeks

Method #2: Using Built-in Functions

Approach:

Import re module using the import Keyword.
Make a single variable to store the path of the file. This is a constant value. This value must be replaced with the file path from your own system in the example below.
Open the file in read-only mode. In this case, we’re simply reading the contents of the file.
Make another variable to store the path of the file. This is a constant value. This value must be replaced with the file path from your own system.
Open another file in write mode. In this case, we’re simply writing the contents of the file.
Give some random prefix as user input using the input() function and store it in a variable.
Iterate through the lines of the file using the for loop and readlines() function.
search all the lines which are having the given prefix using the findall() function and re module(here we used ^ symbol to denote the first word).
Get all the lines which are not having a given prefix using the if and not keywords (here we removed lines that are not given prefix).
If it is true then print the line.
Write the corresponding line to the writeFile using the write() function.
Close the above writing file using the close() function.
Close the above read file using the close() function.
The Exit of Program.

Below is the implementation:

# Import re module using the import Keyword
import re 
# Make a single variable to store the path of the file. This is a constant value.
# This value must be replaced with the file path from your own system in the example below.
givenFilename = "samplefile.txt"
# Open the file in read-only mode. In this case, we're simply reading the contents of the file.
readFile = open(givenFilename, 'r')
# Make another variable to store the path of the file. This is a constant value.
# This value must be replaced with the file path from your own system.
writeFileName = "samplewritefile.txt"
# Open another file in write mode. In this case, we're simply writing the contents of the file.
writingFile = open(writeFileName, 'w')
# Give some random prefix as user input using the input() function and store it in a variable
gvn_prefix = input("Enter some random prefix = ")
# Iterate through the lines of the file using the for loop and readlines() function
for lines in readFile.readlines():
    # search all the lines which are having the given prefix using the findall() function
    # and re module(here we used ^ symbol to denote the first word)
    search = re.findall("^"+gvn_prefix, lines)      
    # Get all the lines which are not having given prefix using the if and not keywords
    # (here we removed lines which are not given prefix)
    if not search: 
        # If it is true then print the line
        print(lines) 
        # Write the corresponding line to the writeFile using the write() function
        writingFile.write(lines) 

# Close the above writing file using the close() function
writingFile.close() 
# Close the above read file using the close() function
readFile.close()

Output:

Enter some random prefix = hello
specific python codes Summary 
good morning this is btechgeeks 
welcome to btechgeeks

File Content: (samplefile.txt)

hello this is btechgeeks sample file 
specific python codes Summary
hello good morning
good morning this is btechgeeks
welcome to btechgeeks

File Content: (samplewritefile.txt)

specific python codes Summary
good morning this is btechgeeks
welcome to btechgeeks

Google Colab Images:

Files and Code:

Program to Remove Lines Starting with any Prefix in Python

Method #1: Using Built-in Functions

Method #2: Using Built-in Functions

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