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How to search and replace text in a file in Python ?

  • Difficulty Level : Hard
  • Last Updated : 14 Sep, 2021

In this article, we will learn how we can replace text in a file using python.

Method 1: Searching and replacing text without using any external module

Let see how we can search and replace text in a text file. First, we create a text file in which we want to search and replace text. Let this file be SampleFile.txt with the following contents:

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To replace text in a file we are going to open the file in read-only using the open() function. Then we will t=read and replace the content in the text file using the read() and replace() functions.

Syntax: open(file, mode=’r’)

Parameters:

  • file : Location of the file
  • mode : Mode in which you want toopen the file.

Then we will open the same file in write mode to write the replaced content.

Python3




# creating a variable and storing the text
# that we want to search
search_text = "dummy"
  
# creating a variable and storing the text
# that we want to add
replace_text = "replaced"
  
# Opening our text file in read only
# mode using the open() function
with open(r'SampleFile.txt', 'r') as file:
  
    # Reading the content of the file
    # using the read() function and storing
    # them in a new variable
    data = file.read()
  
    # Searching and replacing the text
    # using the replace() function
    data = data.replace(search_text, replace_text)
  
# Opening our text file in write only
# mode to write the replaced content
with open(r'SampleFile.txt', 'w') as file:
  
    # Writing the replaced data in our
    # text file
    file.write(data)
  
# Printing Text replaced
print("Text replaced")

Output:

Text replaced

Method 2: Searching and replacing text using the pathlib2 module

Let see how we can search and replace text using the pathlib2 module. First, we create a Text file in which we want to search and replace text. Let this file be SampleFile.txt with the following contents:



Install pathlib2 module using the below command:

pip install pathlib2

This module offers classes representing filesystem paths with semantics appropriate for different operating systems. To replace the text using pathlib2 module we will use the Path method of pathlib2 module.

Syntax: Path(file)

Parameters:

  • file: Location of the file you want to open

In the below code we are replacing “dummy” with “replaced” in our text file. using the pathlib2 module. 

Code:

Python3




# Importing Path from pathlib2 module
from pathlib2 import Path
  
# Creating a function to
# replace the text
def replacetext(search_text, replace_text):
  
    # Opening the file using the Path function
    file = Path(r"SampleFile.txt")
  
    # Reading and storing the content of the file in
    # a data variable
    data = file.read_text()
  
    # Replacing the text using the replace function
    data = data.replace(search_text, replace_text)
  
    # Writing the replaced data
    # in the text file
    file.write_text(data)
  
    # Return "Text replaced" string
    return "Text replaced"
  
  
# Creating a variable and storing
# the text that we want to search
search_text = "dummy"
  
# Creating a variable and storing
# the text that we want to update
replace_text = "replaced"
  
# Calling the replacetext function
# and printing the returned statement
print(replacetext(search_text, replace_text))

Output:

Text replaced



 

Method 3: Searching and replacing text using the regex module

Let see how we can search and replace text using the regex module. We are going to use the re.sub( ) method to replace the text.

Syntax: re.sub(pattern, repl, string, count=0, flags=0)

Parameters:

  • repl : Text you want to add
  • string : Text you want to replace

Code:

Python3




# Importing re module
import re
  
# Creating a function to
# replace the text
def replacetext(search_text,replace_text):
  
    # Opening the file in read and write mode
    with open('SampleFile.txt','r+') as f:
  
        # Reading the file data and store
        # it in a file variable
        file = f.read()
          
        # Replacing the pattern with the string
        # in the file data
        file = re.sub(search_text, replace_text, file)
  
        # Setting the position to the top
        # of the page to insert data
        f.seek(0)
          
        # Writing replaced data in the file
        f.write(file)
  
        # Truncating the file size
        f.truncate()
  
    # Return "Text replaced" string
    return "Text replaced"
  
# Creating a variable and storing
# the text that we want to search
search_text = "dummy"
  
#Creating a variable and storing
# the text that we want to update
replace_text = "replaced"
  
# Calling the replacetext function
# and printing the returned statement
print(replacetext(search_text,replace_text))

Output:

Text replaced

Method 4: Using fileinput

Let see how we can search and replace text using the fileinput module. For this, we will use FileInput() method to iterate over the data of the file and replace the text.

Syntax: FileInput(files=None, inplace=False, backup=”, *, mode=’r’)

Parameters:

  • files : Location of the text file
  • mode : Mode in which you want toopen the file
  • inplace : If value is True then the file is moved to a backup file and
  • standard output is directed to the input file
  • backup : Extension for the backup file

Code:

Python3




# Importing FileInput from fileinput module
from fileinput import FileInput
  
# Creating a function to
# replace the text
def replacetext(search_text, replace_text):
  
    # Opening file using FileInput
    with FileInput("SampleFile.txt", inplace=True,
                   backup='.bak') as f:
  
        # Iterating over every and changing
        # the search_text with replace_text
        # using the replace function
        for line in f:
            print(line.replace(search_text,
                               replace_text), end='')
  
    # Return "Text replaced" string
    return "Text replaced"
  
  
# Creating a variable and storing
# the text that we want to search
search_text = "dummy"
  
# Creating a variable and storing
# the text that we want to update
replace_text = "replaced"
  
# Calling the replacetext function
# and printing the returned statement
print(replacetext(search_text, replace_text))

Output:

Text replaced



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