Search and Replace a Line in a File in Python

Search and replace a line in a file in Python

I guess something like this should do it. It basically writes the content to a new file and replaces the old file with the new file:

from tempfile import mkstemp
from shutil import move, copymode
from os import fdopen, remove

def replace(file_path, pattern, subst):
    #Create temp file
    fh, abs_path = mkstemp()
    with fdopen(fh,'w') as new_file:
        with open(file_path) as old_file:
            for line in old_file:
                new_file.write(line.replace(pattern, subst))
    #Copy the file permissions from the old file to the new file
    copymode(file_path, abs_path)
    #Remove original file
    remove(file_path)
    #Move new file
    move(abs_path, file_path)

Search and replace lines in a file in python

with open('Text.txt','r') as f:
    file_data = f.readlines()


i=0
while i in range(len(file_data)):
    for line in file_data:
        if file_data[i].lstrip().startswith('if') and ('|' in line):          
            file_data[i]= file_data[i].replace(' | ', ' || ')
    i+=1
file_data_str = ''.join(file_data)

with open('Text.txt','w') as f:
    f.write(file_data_str) 

This should work.

Fastest way to find and replace specific line in a large text file with Python

I assume your memory can store the whole file. This should be faster by using regex:

import re
number = 407597693
with open("numbers.txt", "r") as f:
    data = f.read()
    # data = re.sub(f'({number}):(.*)', lambda x:f"{x.group(1)}:{float(x.group(2))+3600}", data)
    data = re.sub("^" + str(number) + ".*\n", str(number) + ":" + str(int(time.time()) + 3600) + "\n", data, flags=re.MULTILINE)
with open("numbers.txt", "w") as f:
    f.write(data)

Python: replace line in file starting with a pattern

You don't need to know what old is; just redefine the entire line:

import sys
import fileinput
for line in fileinput.input([filename], inplace=True):
    if line.strip().startswith('initial_mass = '):
        line = 'initial_mass = 123\n'
    sys.stdout.write(line)

How to find and replace a line in a text file?

This is a lot easier when you configure your text file to be key:value pairs (like the dict construct in python, or values in another DB like SQL). Then you can simply set a sentinel value when the value is met, then unset when you've replaced the correct line.

So, if changing the format of text to:

ProductCode <value>
ProductName <value>
Price <value>
CurrentStock <value>
ReorderStock <value>
Targetstock <value>

Then you can do something like this:

ProductCode = "28273139"
NewStock = "29"
SentinelValue = 0

with open('myDB.txt', 'r+') as database:
  for line in database:
  (key, val) = line.split()
  if key == "ProductCode":
    if val == ProductCode:
      SentinelValue = 1
  if key != "ProductCode":
    if key == "CurrentStock":
      if SentinelValue == 1:
        line = line.replace(val, NewStock)
    print line

It is a bit dirty and could surely be cleaned up, but it is much more verbose. Also, note that the space is important as it is used as the delimiter when splitting the lines.

You may also notice I didn't write to the file: At least for me in python 2.7, there seems to be an issue where I can't replace a line of text, only append with f.write(). This code works and replaces to stdout, the workaround for writing to a file is to simply write all lines to a new file:

ProductCode = "28273139"
NewStock = "29"
SentinelValue = 0
fout = open('newDB.txt', 'w')

with open('myDB.txt', 'r+') as database:
  for line in database:
  (key, val) = line.split()
  if key == "ProductCode":
    if val == ProductCode:
      SentinelValue = 1
  if key != "ProductCode":
    if key == "CurrentStock":
      if SentinelValue == 1:
        line = line.replace(val, NewStock)
    fout.write(line)
    print line

You could then write logic to replace the files as needed. However, I would very much suggest looking at how to write and read from an actual SQL database. I hope this helps! ^^

Search the word, and replace the whole line containing the word in a file in Python using fileinput

I realized that I was wrong by just an indentation. In the code piece 1 mentioned in the question, if I am bringing the 'print line,' from the scope of if i.e. if i outdent it, then this is solved...

As this line was inside the scope of if, hence, only this new_text was being written to the file, and other lines were not being written, and hence the file was left with only the new_text. So, the code piece should be as follow :-

text = "mov9 = "   # if any line contains this text, I want to modify the whole line.
new_text = "mov9 = Alice in Wonderland"
x = fileinput.input(files="C:\Users\Admin\Desktop\DeletedMovies.txt", inplace=1)
for line in x:
    if text in line:
        line = new_text
    print line,
x.close()

Also, the second solution given by Rolf of Saxony & the first solution by Padraic Cunningham is somehow similar.

Replace only first line of text file in python

You can use the readlines and writelines to do this.
For example, I created a file called "test.txt" that contains two lines (in Out[3]). After opening the file, I can use f.readlines() to get all lines in a list of string format. Then, the only thing I need to do is to replace the first element of the string to whatever I want, and then write back.

with open("test.txt") as f:
    lines = f.readlines()

lines # ['This is the first line.\n', 'This is the second line.\n']

lines[0] = "This is the line that's replaced.\n"

lines # ["This is the line that's replaced.\n", 'This is the second line.\n']

with open("test.txt", "w") as f:
    f.writelines(lines)

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