Search and replace string inside .txt file with user input

Question

Background: I am trying to automate some parts of a work process. Manual steps I take: I get a ticket to change an ID inside a text file. I have to go through a network shared folder, create a backup of the file, push the copied file into an archive folder, and edit the existing file with the ID from the ticket.

What I am trying to create: A small program that will ask me what ID I am wanting to change(there are pre-existing ID's inside the text file) then it will go inside the file and find the match. Then I want the program to ask me what I want to change the ID to. I want the program to edit the existing file with my input, save it, then close it.

So far I have the following code that completes the first portion (copying the file and pushing it into the archive folder). I have the second function which I am stuck on. I know the second function isn't working, but would like input from others on what they think I should try. I have seen the fileinput module, but I have read that it's not the best module and I should try to program this without the fileinput module.

Code:

import shutil
import datetime
import os
import fileinput

original_file = "\\network\\path\\to\\file"

def date_rename_file():
    todays_date = datetime.datetime.now()
    stripped_time = todays_date.strftime('%Y%m%d')    
    shutil.copyfile(original_file, "\\network\\path\\to\\backupfolder\\device_"+str(stripped_time)+".txt")

def device_id_replace():
    original_id = input("What device ID are you needing to replace?")
    new_id = input("What is the new device ID?")
    with open(original_file, 'w') as devicetxt:
        for line in devicetxt:
            print(line)
            if original_id in line:
                print("Found "+original_id)

date_rename_file()
device_id_replace()

Thanks, feel free to demolish my code :) I'm still learning and would appreciate any input. Also, feel free to let me know if I left any pertinent information out!

Answer 1

You can try this:

def device_id_replace():
    original_id = input("What device ID are you needing to replace?")
    new_id = input("What is the new device ID?")
    with open(original_file, 'r+') as devicetxt: #r+ is for read and write
        string = devicetxt.read() #read into one string
        string = string.replace(original_id, new_id) #replacement
        devicetxt.truncate(0) #To clear contents of file before writeback
        devicetxt.seek(0) #Put the file's current position at 0
        devicetxt.write(string) #writeback to file

Also, it is better practice to pass the original_file as a string to the functions. See editted code below:

import shutil
import datetime
import os
import fileinput

original_file = "\\network\\path\\to\\file"

def date_rename_file(filepath):
    todays_date = datetime.datetime.now()
    stripped_time = todays_date.strftime('%Y%m%d')    
    shutil.copyfile(filepath, "\\network\\path\\to\\backupfolder\\device_"+str(stripped_time)+".txt")

def device_id_replace(filepath):
    original_id = input("What device ID are you needing to replace?")
    new_id = input("What is the new device ID?")
    with open(filepath, 'r+') as devicetxt: #r+ is for read and write
        string = devicetxt.read() #read into one string
        string = string.replace(original_id, new_id) #replacement
        devicetxt.truncate(0) #To clear contents of file before writeback
        devicetxt.seek(0) #Put the file's current position at 0
        devicetxt.write(string) #writeback to file

date_rename_file(original_file)
device_id_replace(original_file)

Answer 2

Try this one:

original_file = ""\\network\\path\\to\\file""

def device_id_replace(filepath):                   
    original_id = input("What device ID are you needing to replace?") 
    new_id = input("What is the new device ID?")   
    with open(filepath, 'r') as devicetxt:
        new_content = []
        for line in devicetxt:
            new_content.append(line.replace(original_id, new_id))
    with open(filepath, "w") as devicetxt:
        for line in new_content:
            devicetxt.write(line)

device_id_replace(original_file)

The answer of @ycx was not working in the past. So I fixed your old code:

original_file = "test.txt"


def device_id_replace(filepath):
    original_id = input("What device ID are you needing to replace?")
    new_id = input("What is the new device ID?")
    with open(filepath, 'r+') as devicetxt: #r+ is for read and write
        contents = devicetxt.readlines() #put all lines into a list
        for line_i, line in enumerate(contents):
            if original_id in line:
                contents[line_i] = line.replace(original_id, new_id) # CHANGED LINE
        devicetxt.truncate(0)
        devicetxt.seek(0)
        devicetxt.writelines(contents) #writeback to file

device_id_replace(original_file)

Answer 3

You have a few options here, either use an internal tool like sed if you are using Unix/Unix like, or create a new file on top of the old one.

1. Read all the file.
2. Replace occurrences.
3. Rewrite all lines.

This a pythonic version

with open(filepath) as f:
    transformedLines = [line.replace(old, new) if (old in line) else (line) for line in f]
with open(filepath, 'w') as f:
    f.writelines(transformedLines);

A less Pythonic version is similar:

transformedLines = []
with open(filepath) as f:
    for line in f:
        if old in line:
            transformedLines.append(line.replace(old, new))
        else:
            transformedLines.append(line)

A functional way (albeit very inefficient) can be done with map:

    transformedLines = list(map(lambda line : line.replace(old, new), f.readlines()))

This should be alright if your file isn’t huge, otherwise you will have to think about using a different type of data store like a DB.

Your approach works well at the moment but you will want to open it in read mode, for each line append it to a new list, if your id is found append the new line instead.

Write the new array to the file opened in write mode, which will wipe out the contents.