In Python, there is no need for importing an external library to read and write files. Python provides an inbuilt function for creating, writing, and reading files.

In this file handling in Python tutorial, we will learn:

How to Open a Text File in Python

To open a file, you need to use the built-in open function. The Python open file function returns a file object that contains methods and attributes to perform various operations for opening files in Python.

Syntax of Python open file function

file_object  = open("filename", "mode")

Here,

  • filename: gives the name of the file that the file object has opened.
  • mode: attribute of a file object tells you which mode a file was opened in.

More details of these modes are explained below

How to Create a Text File in Python

With Python Write to File, you can create text files (novicekoder.txt) by using the code, we have demonstrated here:

Step 1) 

	f= open("novicekoder.txt","w+")
  • We declared the variable f to open a file named novicekoder.txt. Open takes 2 arguments, the file that we want to open and a string that represents the kinds of permission or operation we want to do on the file
  • Here, we used the "w" letter in our argument, which indicates Python write to file and it will create a file if it does not exist in the library
  • Plus sign indicates both read and write for Python create file operation.

Step 2) 

for i in range(10):
     f.write("This is line %d\r\n" % (i+1))
  • We have a for loop that runs over a range of 10 numbers.
  • Using the write function to enter data into the file.
  • The output we want to iterate in the file is "this is line number", which we declare with Python write to text file function and then percent d (displays integer)
  • So basically we are putting in the line number that we are writing, then putting it in a carriage return and a new line character

Step 3) 

	f.close()
  • This will close the instance of the file novicekoder.txt stored

Here is the result after code execution for Python create file


When you click on your text file in our case "novicekoder.txt" it will look something like this


How to Append to a File in Python

You can also append/add a new text to the already existing file or a new file.

Step 1) 

f=open("novicekoder.txt", "a+")

Once again if you could see a plus sign in the code, it indicates that it will create a new file if it does not exist. But in our case we already have the file, so we are not required to create a new file for Python append to file operation.

Step 2) 

for i in range(2):
     f.write("Appended line %d\r\n" % (i+1))

This will write data into the file in append mode.


You can see the output in the "novicekoder.txt" file. The output of the code is that earlier file is appended with new data by Python append to file operation.


How to Read Files in Python

You can read a file in Python by calling the .txt file in a "read mode"(r).

Step 1) Open the file in Reading mode 

	f=open("novicekoder.txt", "r")

Step 2) We use the mode function in the code to check that the file is in open mode. If yes, we proceed ahead 

	if f.mode == 'r':

Step 3) Use f.read to read file data and store it in variable content for reading files in Python 

	contents =f.read()

Step 4) Print contents for Python read a text file

Here is the output of the Python read file example:


How to Read a File line by line in Python

You can also read your .txt file line by line if your data is too big to read. readlines() code will segregate your data in easy to read mode.


When you run the code (f1=f.readlines()) to read file line by line in Python, it will separate each line and present the file in a readable format. In our case the line is short and readable, the output will look similar to the read mode. But if there is a complex data file which is not readable, this piece of code could be useful.

File Modes in Python

Following are the various File Modes in Python:

Mode Description
'r' This is the default mode. It opens a file for reading.
'w' This Mode Opens a file for writing.
If a file does not exist, it creates a new file.
If the file exists it truncates the file.
'x' Creates a new file. If the file already exists, the operation fails.
'a' Open file in append mode.
If a file does not exist, it creates a new file.
't' This is the default mode. It opens in text mode.
'b' This opens in binary mode.
'+' This will open a file for reading and writing (updating)

Here is the complete code for Python print() to File Example

Python 2 Example 

def main():
     f= open("novicekoder.txt","w+")
     #f=open("novicekoder.txt","a+")
     for i in range(10):
         f.write("This is line %d\r\n" % (i+1))
     f.close()   
     #Open the file back and read the contents
     #f=open("novicekoder.txt", "r")
     #   if f.mode == 'r': 
     #     contents =f.read()
     #     print contents
     #or, readlines reads the individual line into a list
     #fl =f.readlines()
     #for x in fl:
     #print x
if __name__== "__main__":
  main()

Python 3 Example

Below is another Python print() to File Example: 

def main():
    f= open("novicekoder.txt","w+")
    #f=open("novicekoder.txt","a+")
    for i in range(10):
         f.write("This is line %d\r\n" % (i+1))
    f.close()
    #Open the file back and read the contents
    #f=open("novicekoder.txt", "r")
    #if f.mode == 'r':
    #   contents =f.read()
    #    print (contents)
    #or, readlines reads the individual line into a list
    #fl =f.readlines()
    #for x in fl:
    #print(x)
if __name__== "__main__":
  main()

Conclusion

  • Python allows you to read, write and delete files
  • Use the function open("filename","w+") for Python create text file. The + tells the python interpreter for Python open text file with read and write permissions.
  • To append data to an existing file or Python print to file operation, use the command open("Filename", "a")
  • Use the Python read file function to read the ENTIRE contents of a file
  • Use the readings function to read the content of the file one by one.