Python 3 string replace() method + Python replace a string in a file

In this Python tutorial, we will discuss how to use Python 3 string replace() method with a few examples. Also, we will see, how to replace a string in a file in Python. We will discuss the below examples:

  • Python 3 string replace() method
  • Replace a letter in a string python
  • Python replace a string in a file
  • How to replace a string in a file in Python
  • Python replace a string in file regex
  • Python replace a string in a file using a dictionary
  • Python replace a string in a CSV file
  • Python replace a string in the XML file
  • Python replace multiple strings in a file
  • Python replace a string in a text file
  • Python code to replace a string in a file

Python 3 string replace() method

Let us see, how to use Python 3 string replace() method.

Python replace() method is an inbuilt function in Python. The replace() method returns a copy of the string in which the occurrences of old are replaced with new.

Example:

my_string = "Python"
s = my_string.replace("Python", "PythonGuides")
print(s)

After writing the above code (python 3 string replace), you will print “s” then the output will appear as “ PythonGuides ”. Here, the replace() method replaces the specified string with another specified string.

You can refer to the below screenshot python 3 string replace() method.

Python 3 string replace
Python 3 string replace() method

This is a simple example of Python string replace() method.

Read: Python remove substring from a String

Replace a letter in a string python

The replace() is an inbuilt function in python programming which is used to replace a letter in a string and it returns a copy of the string after replacing.

Example:

str = ['P', 'y', 't', 'h', 'o', 'n', 'g', 'u', 'i', 'd', 'e', 's']
str[6] = 'G'
print (str)

To get the output when you will print(str) then it will return a copy of the string after replacing the letter from the string. So, str[6] index is replaced with ‘G’ in the output.

You can refer to the below screenshot replace a letter in a string python.

Replace a letter in a string python
Replace a letter in a string python

Python replace a string in a file

Replace a string gives us the ability to replace content and the shrimp by creating a new file showing with the replaced contact.

  • It is used for removing a specified character or substring from another one.
  • Replace[] method which replaces one pattern from another and returns a new string as a result.

Syntax:

Here is the syntax of replace[]

replace[
        old_str1,
        new_str2,
        instance
]

In python, there are two types of files binary and text. So either file gets to be a binary that contains 0 and 1 or it can have some literal text.

Text files are structured as a sequence of lines where each line includes characters. Every line is terminated with the special character is called EOL [End of line character].

How to replace a string in a file in Python

  • Let us see, how to replace a string in a file in Python.
  • Let’s take an example, we will replace a string file with python in the test.txt file, and overwrite the test.txt file with the replaced text.

Syntax:

Here is the syntax of replace a string in a file.

str = open (" .txt"," ")
data = str.read()

Example

#read input file
str1 = open("/home/arvind/Documents/test.txt", "rt")
data = str1.read()
data = data.replace('python', 'pyton')
#close the input file
str1.close()
str1 = open("/home/arvind/Documents/test.txt", "wt")
#overwrite the input file
str1.write(data)
str1.close()
print(data)

Here is the screenshot of the following given code.

Python replace string in file
Python replace string in file

The above Python code we can use to replace a string in a file in Python.

Python replace a string in file regex

  • In this section, we will learn how to replace a string in a file using regex in Python.
  • Regular Expression is basically used for describing a search pattern so you can use regular expression for searching a specific string in a large amount of data.
  • You can verify that string has a proper format or not you can find a string and replace it with another string and you can even format the data into a proper form for importing so these are all uses of the regular expression.
  • Use the regex module we have used two functions that are
    • re.compile()
    • re.escape()
  1. re.compile() is used to compile a regex pattern.
  2. re.escape() is used to escape characters in regex pattern.

Syntax:

re.compile(re.escape(text)
pattern.sub(subs)

Example

Let’s take an example to check how to replace a string in file regex.

import re
def replace(filePath, text, subs, flags=0):
    
   #open file
   with open(filepath, "r+") as file:
       #read the contents
       contents = file.read()
       text_pattern = re.compile(re.escape(text), flags)
       contents = text_pattern.sub(subs, contents)
       file.seek(0)
       file.truncate()
       file.write(contents)
       
filepath="/home/arvind/Documents/test.txt"
text="pyton"
subs="tinkter"
#calling the replace method
replace(filepath, text, subs)
print(subs)

Here is the screenshot of following given code.

Python replace string in file regex
Python replace string in file regex

The above Python code, we can use to replace a string in file using regex in Python.

Python replace a string in a file using a dictionary

  • In this section, we will learn how to replace a string in a file using a Dictionary in Python.
  • We can easily use the regex method that is basically used for describing a search pattern so you can use regular expression for searching a specific string in a large amount of data.

Syntax:

text = re.sub(" .txt",k,l,text)
str4= replace_all(str4,dict)

Example

Let’s take an example to check Python replace a string in a file using a Dictionary

import re

dict1 = {1:'a',2:'b',3:'c'} 

f3 = open("/home/arvind/Documents/test.txt","r")
str4 = f3.read() 

def replace_all(text, dic):
    for k, l in dic.items():
        text = re.sub(r"\b%s\b"%k, l, text) 
        
    return text

str4 = replace_all(str4,dict1)
print(str4) 

Here is the screenshot of the following given code.

Python replace a string in file using dictionary
Python replace a string in file using Dictionary

Read: How to convert dictionary to JSON in Python

This is how to replace a string in a file using a dictionary in Python.

Python replace a string in a CSV file

In this section, we will learn how to replace a string in a CSV file in Python. For replacing a string in a CSV file we can easily use the method replace().

Syntax:

str4=str4.replace("ID NUMBER","UNIQUE ID")

Example

Let’s take an example to check how to replace a string in a csv file.


str4 = open("/home/arvind/Documents/app.csv", "r")
str4 = ''.join([i for i in str4]) 
str4 = str4.replace("ID NUMBER", "UNIQUE ID") 

y = open("output.csv","w")
  
y.writelines(str4)
y.close()
print(str4)

Here is the screenshot of following given code.

Python replace string in csv file
Python replace string in csv file

Python replace a string in the XML file

  • XML stands for an extensible Markup language. It is similar to HTML in its appearance but XML is used for data preparation while HTML is used to define what data is being used.
  • XML is exclusively designed to send and receive data back between clients and servers.
  • XML is also a metalanguage this means, XML can be used to describe another markup language like XHTML, SVG, RDF.
  • XML was developed as a standard for data storage and data exchange.
  • The main advantages of XML are
    • XML is device and platform-independent.
    • XML is not written in binary language.
    • XML is human and machine-readable.
  • In this section, we will learn how to replace a string in the XML file.
  • For replacing a string in an XML file we can easily use the pop() method.

Example

Let’s take an example to check how to replace a string in the XML file

import xml.etree.ElementTree as ET

tree = ET.parse("/home/arvind/Documents/test.xml")
root = tree.getroot()
root[0][0].attrib.pop('name', None)
 
tree.write('output.xml')
print(root)

Read: Python Pandas CSV Tutorial

Python replace multiple strings in a file

  • In this section, we will learn how to replace multiple strings in a file in Python.
  • For replacing multiple strings in a file we can easily use replace() method.

Example

Let’s take an example to check how to replace multiple strings in a file

str1 = open("/home/arvind/Documents/test.text", "rt")
data = str1.read()
data = data.replace('java is ', ' C++ is a')
#close the input file
str1.close()
str1 = open("/home/arvind/Documents/test.txt", "wt")
#overwrite the input file
str1.write(data)
str1.close()
print(data)

Here is the Screenshot of following given code

Python replace multiple strings in a file
Python replace multiple strings in a file

Read: How to write Python array to CSV

Python replace a string in a text file

Replace a string gives us the ability to replace content and the shrimp by creating a new showing with the replace contact.

  • It is used for removing a specified character or substring from another one.
  • Replace[] method which replaces one pattern from another and returns a new string as a result.
  • In this section, we will learn how to replace a string in a file.
  • Let’s take an example, we will replace a string file with python in the test.txt file, and overwrite the test.txt file with the replaced text.

Syntax:

Here is the syntax of replace[]

replace[
        old_str1,
        new_str2,
        instance
]

Example

Let’s take an example to check how to replace a string in a text file

#read input file
str1 = open("/home/arvind/Documents/test.txt", "rt")
data = str1.read()
data = data.replace('mongodb', 'SQL')
#close the input file
str1.close()
str1 = open("/home/arvind/Documents/test.txt", "wt")
#overwrite the input file
str1.write(data)
str1.close()
print(data)
Python replace a string in a text file
Python replace a string in a text file

Read: Python Read CSV File and Write CSV File

Python code to replace a string in a file

  • In this section, we will learn how to Python code to replace a string in a file.
  • Let’s take an example, we will replace a string file with python in the test.txt file, and overwrite the test.txt file with the replaced text.

Example

Let’s take an example to check how to Python code to replace a string in a file

#read input file
str1 = open("test.txt", "rt")
data = str1.read()
data = data.replace('Python', 'JAVA')
#close the input file
str1.close()
str1 = open("test.txt", "wt")
#overwrite the input file
str1.write(data)
str1.close()
print(data)

Here is the screenshot of following given code

Python code to replace a string in a file
Python code to replace a string in a file

This is how to replace a string in a file in Python.

You may like the following Python tutorials:

In this Python tutorial, we learned, how to use Python 3 string replace() method with a few examples.

  • Python 3 string replace() method
  • Replace a letter in a string python
  • Python replace a string in a file
  • How to replace a string in a file in Python
  • Python replace a string in file regex
  • Python replace a string in a file using a dictionary
  • Python replace a string in a CSV file
  • Python replace a string in the XML file
  • Python replace multiple strings in a file
  • Python replace a string in a text file
  • Python code to replace a string in a file