Python File Handling Tutorial

Python provides robust support for managing files, allowing users to perform operations such as reading from and writing to files with ease. The ability to handle files is crucial, particularly when there is a need to retain data permanently within a file. A file serves as a designated space on the disk to hold associated data. This stored information remains accessible (non-volatile) even after the program has concluded.

In Python, files can be handled in two distinct modes: text mode or binary mode. A file can exist in either text or binary format, with each line concluding with a specific character, such as a comma (,) or a newline character. Python processes code sequentially, executing one line at a time before prompting the interpreter to begin the next line. This operation is an ongoing cycle within the Python environment.

Why do we need File Handling?

We need file handling for various purposes such as:

• ✅ We can safely save our data even after the program terminates.
• ✅ We can access various types of files, like .txt, .json, and .csv files.
• ✅ Without using a lot of memory, we can manage large files much efficiently.
• ✅ Using the file handling, we can automate various tasks such as reading configs or saving the output.
• ✅ We can also handle input/output operations in real-world applications and tools using file handling.

A file operation can be done in the following order:

• ✅ Open a file
• ✅ Read or write - which is a performing operation
• ✅ Close the file

1. Opening a file

A file operation begins with the process of opening the file. Initially, you need to open the File, after which Python will commence the operation. The opening of a file is accomplished using the open function in Python. This function requires two parameters: the name of the file and the mode of access that dictates how the file is to be interacted with. It is essential to define the mode when invoking the open function. Upon execution, the function provides a file object, which can then be utilized to carry out a range of tasks, such as reading and writing.

Syntax:

It has the following syntax:

file object = open(<file-name>, <access-mode>, <buffering>)

Files can be accessed through multiple modes such as reading, writing, or appending. Below are the specifics regarding the access modes utilized when opening a file.

Python Example for Opening a file

Let's consider an example that illustrates the process of opening a file in Python.

#opens the file file.txt in read mode

fileptr = open("file.txt","r")

if fileptr:

    print("file is opened successfully")

Output:

<class '-io.TextIOWrapper'>

The file is opened successfully

Explanation:

In the code provided above, the filename is supplied as the initial argument, and the file is accessed in read mode by specifying 'r' as the second argument. The variable fileptr contains the file object, and if the file is opened without issues, the subsequent print statement will be executed.

2. Reading a File

To access the contents of a file with a Python script, the language offers the read function. This function retrieves a string from the specified file. It is capable of processing data in both text and binary formats.

Syntax:

It has the following syntax:

fileobj.read(<count>)

In this context, the count refers to the total number of bytes that will be read from the file, commencing from the file's start. If the count parameter is omitted, the operation may read through the file's entire content until it reaches the end.

Python Example for read Method

To illustrate the process of reading a file using Python, let’s consider a practical example.

#open the file.txt in read mode. Causes an error if no such file exists.

fileptr = open("file2.txt","r")

#stores all the data of the file into the variable content

content = fileptr.read(10)

# prints the type of the data stored in the file

print(type(content))

#prints the content of the file

print(content)

#closes the opened file

fileptr.close()

Output:

<class 'str'>

Python is

Explanation:

In the code presented above, the content of file2.txt has been accessed utilizing the read method. We specified a count parameter of ten, indicating that the method will retrieve the initial ten characters from the file.

Read Lines of the file

Python provides the capability to read a file one line at a time through the use of the readline method. This method retrieves the lines from the file starting at the very beginning.

As an illustration, invoking the readline function twice enables us to retrieve the initial two lines from the file. In essence, the readline method facilitates the reading of a single line at any given moment.

Python Example to Read Lines of the File:

To illustrate the process of reading lines from files with the readline function in Python, we can consider the following example.

#open the file.txt in read mode. It may cause an error if no such file exists.

fileptr = open("file2.txt","r");

#stores all the data of the file into the variable content

content = fileptr.readline()

content1 = fileptr.readline()

#prints the content of the file

print(content)

print(content1)

#closes the opened file

fileptr.close()

Output:

Python is a modern-day language.

It makes things so simple.

Explanation:

We invoked the readline function two times; consequently, it retrieved two lines from the file. This implies that if you invoke the readline function n times within your program, it will read n lines from the file. This demonstrates the functionality of the readline function in Python. Additionally, Python offers the readlines method, which serves the purpose of reading multiple lines. It returns a list of lines until the end of the file (EOF) is encountered.

Python Example for Write Mode

This is a write operation in Python. We begin by opening an already existing file using the provided code, after which we proceed to write to it. Below is an example to illustrate this:

file = open('file.txt','w')

file.write("Here we write a command")

file.write("Hello users of our site")

file.close()

Output:

> Hi

ERROR!

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

NameError: name 'Hi' is not defined

3. The close Method

The close method serves the purpose of concluding the program's execution. After completing all tasks involving the file, it is essential to close it via the Python script by utilizing the close method. Any data that has not been written will be lost when the close method is invoked on the file object. It is considered a best practice to ensure the file is closed after all operations have been finalized.

Syntax:

It has the following syntax:

fileobject.close()

Python Example for Closing Method

Let's consider an example to illustrate the process of closing a file in Python.

# opens the file file.txt in read mode

fileptr = open("file.txt","r")

if fileptr:

    print("The existing file is opened successfully in Python")

#closes the opened file

fileptr.close()

Once the file is closed, no further operations can be executed on it. It is essential to ensure that the file is closed correctly. If an exception arises during any file operations, the program may end abruptly without properly closing the file. To address this issue, we should implement the following method.

try:

   fileptr = open("file.txt")

   # perform file operations

finally:

   fileptr.close()

4. The with statement

The with statement made its debut in Python version 2.5. This statement proves to be advantageous when handling files. It is particularly beneficial in situations where two statements need to be executed with a block of code situated in between them.

Syntax:

It has the following syntax:

with open(<file name>, <access mode>) as <file-pointer>:

    #statement suite

Python Example to demonstrate with Statement

To illustrate the usage of the with statement in Python file manipulation, let's consider an example.

with open("file.txt", 'r') as f:

    content = f.read();

    print(content)

File Related Methods

The file object includes a variety of methods that allow for the management of files across different operating systems.

Conclusion

In this guide, we will provide an overview of file management in Python. Python allows users to effectively manage files, including reading from and writing to them. In this tutorial, we will explore different functions available in Python that facilitate the processes of reading, writing, deleting, and opening files. Each of these functions will be illustrated with examples, their corresponding outputs, and comprehensive explanations.

Python File Handling FAQs

1. How can we open a file in Python?

In Python, we can utilize the built-in open function to access a file. Let’s explore the process:

f = open("file.txt", "r")  # "r" = read mode

In this instance, we need to substitute "file.txt" with the actual name of the file.

2. What are the different file modes available in Python?

There are various file modes available in Python, such as:

• ✅ "r" → Read (default, error if file doesn't exist)
• ✅ "w" → Write (creates new or overwrites existing file)
• ✅ "a" → Append (adds data at the end of the file)
• ✅ "x" → Create (error if file already exists)
• ✅ "b" → Binary mode (e.g., "rb", "wb")
• ✅ "t" → Text mode (default, e.g., "rt", "wt")

3. How do we read from a file?

To access data from a file, we can utilize the "r" mode along with the read function, readline function, and readlines function. Let's explore this further with an illustrative example:

Code:

with open("file.txt", "r") as f:

    content = f.read()      # To Read the entire file

    line = f.readline()     # To Read one line

    lines = f.readlines()   # To read all lines into a list

4. How do we write to a file?

To write data to a file, we can utilize the "w" mode in conjunction with the write and writelines functions. Let’s explore this with an example in code:

Code:

with open("file.txt", "w") as f:

    f.write("Hello World\n")

    f.writelines(["Line1\n", "Line2\n"])

5. How can we read/write a CSV file?

import csv

# Write to a CSV file

with open("data.csv", "w", newline="") as f:

    writer = csv.writer(f)

    writer.writerow(["Name", "Age"])

    writer.writerow(["Example", 14])

# Read to a CSV file

with open("data.csv", "r") as f:

    reader = csv.reader(f)

    for row in reader:

        print(row)