Reading and Writing Text and Numbers from/to a File

Reading Text Files in Python

Python provides several methods to read the contents of a text file.

Opening a File

The first step is to open the file using the open() function. The function takes two arguments: the filename and the mode. The most common mode for reading is 'r'.

Python

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

  # Perform file operations here

The with statement ensures proper closing of the file even if an exception occurs.

Reading Methods

There are three primary methods to read the contents of a file:

1. read()

Reads the entire contents of the file as a single string.

Python

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

  content = file.read()

  print(content)

2. readline()

Reads a single line from the file.

Python

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

  line = file.readline()

  print(line)

3. readlines()

Reads all lines of the file and returns them as a list of strings.

Python

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

  lines = file.readlines()

  for line in lines:

    print(line, end='')

Additional Considerations

·         Encoding: If you know the character encoding of the file, you can specify it using the encoding parameter in the open() function.

·         Error handling: Use try-except blocks to handle potential errors like file not found or permission denied.

·         Large files: For large files, consider reading the file in chunks using read(size) to avoid loading the entire file into memory.

Example:

Python

with open('my_file.txt', 'r', encoding='utf-8') as file:

  for line in file:

    line = line.strip()  # Remove leading/trailing whitespace

    if line:  # Skip empty lines

      print(line)

By understanding these methods and considerations, you can effectively read text files in your Python applications.

Writing to a Text File in Python

Opening a File for Writing

To write to a text file in Python, you'll use the open() function with the 'w' mode (write) or 'a' mode (append).

·         'w': Overwrites the entire file if it exists or creates a new file if it doesn't.

·         'a': Appends data to the end of the file, creating the file if it doesn't exist.

Python

with open('my_file.txt', 'w') as file:

  # Write to the file

Writing to the File

Use the write() method to write strings to the file:

Python

with open('my_file.txt', 'w') as file:

  file.write("This is the first line.\n")

  file.write("This is the second line.\n")

Writing Multiple Lines

You can write multiple lines using a loop or by creating a list of strings and using the writelines() method:

Python

lines = ["Line 1\n", "Line 2\n", "Line 3\n"]

with open('my_file.txt', 'w') as file:

  file.writelines(lines)

Important Considerations

·         Encoding: Specify the encoding if needed using the encoding parameter in the open() function.

·         Error Handling: Use try-except blocks to handle potential errors like file not found or permission denied.

·         Closing the File: The with statement automatically closes the file, but you can also use file.close() explicitly.

Example

Python

import datetime

with open('log.txt', 'a') as file:

  now = datetime.datetime.now()

  file.write(f"{now}: Something happened.\n")

This code appends a timestamped message to an existing log file.

Deleting a File

To delete a file in Python, you'll use the os module's remove() function. However, it's essential to check if the file exists before attempting to delete it to avoid errors.

Python

import os

def delete_file_if_exists(file_path):

  """Deletes a file if it exists."""

  if os.path.exists(file_path):

    os.remove(file_path)

    print(f"File '{file_path}' deleted successfully.")

  else:

    print(f"File '{file_path}' not found.")

# Example usage:

file_to_delete = "my_file.txt"

delete_file_if_exists(file_to_delete)

Explanation:

1.     Import the os module: This module provides functions for interacting with the operating system.

2.     Define a function: The delete_file_if_exists function takes the file path as input.

3.     Check file existence: Use os.path.exists() to verify if the file exists.

4.     Delete the file: If the file exists, use os.remove() to delete it.

5.     Handle non-existent file: If the file doesn't exist, print a message indicating so.

Key points:

·         Always check for file existence before deletion to avoid errors.

·         Use os.path.exists() to verify file existence.

·         Employ os.remove() to delete the file.

·         Provide informative messages for success or failure.

By following these steps, you can safely delete files in your Python scripts without encountering errors.