Adventures in Machine Learning

Mastering File Reading in Python: Types Methods and Use Cases

File types and methods for reading

1. Text Files

Python can read several types of files, including text and CSV files. Text files are plaintext files that contain no formatting information.

2. CSV Files

CSV (comma-separated values) files are used to store data in tabular form, with each row separated by a newline and each column separated by a comma.

3. Python File Reading Methods

  • read(): Reads the entire file and returns its contents as a string.
  • readline(): Reads a single line from the file.
  • readlines(): Reads all the lines in the file and returns them as a list.

Access modes for reading a file

To read a file in Python, we need to specify the access mode. The access mode is a string that specifies the purpose of opening the file. Here are some common access modes:

  • ‘r’: Used for reading an existing file.
  • ‘r+’: Used for both reading and writing.
  • ‘w+’: Used for reading and writing, truncating the file if it exists.
  • ‘a+’: Appends content to an existing file.
  • ‘rb’: Used for reading a binary file.

Steps for reading a file in Python

  1. Specify the file’s path: The path is the location on the computer where the file is stored.
  2. Open the file using the open() function: Specify the access mode you want to use.
  3. Use a read method to read the file’s contents: For example, use read(), readline(), or readlines().
  4. Close the file using the close() function: This is crucial to release resources.

Error Handling

When opening an existing file, it’s important to handle errors such as FileNotFoundError. You can use a try-except-finally block to catch exceptions and release resources.

Example: Reading a text file

Let’s say we have a text file named ‘example.txt’ that contains the phrase “Hello, world!”.

Using absolute path:

try:
    file = open('C:UsersUserDocumentsexample.txt', 'r')
    content = file.read()
    print(content)
  finally:
    file.close()

Using the with statement:

try:
    with open('example.txt', 'r') as file:
      content = file.read()
      print(content)
  except FileNotFoundError:
    print("The file does not exist.")

Read text file line by line

We can use the readline() method to read one line at a time, or a for loop to iterate through each line in the file.

with open('lines.txt', 'r') as file:
    for line in file:
      print(line)

Example: Reading and writing to the same file

We can use the ‘r+’ mode to read and write to the same file simultaneously. However, writing without first seeking to a specific position can cause an UnsupportedOperation exception.

try:
    with open('example.txt', 'r+') as file:
      content = file.read()
      file.write(' world!')
      print(content)
  except FileNotFoundError:
    print("The file does not exist.")
  except UnsupportedOperation:
    print("Cannot write to file.")

Another approach is to use a temporary file to avoid the UnsupportedOperation exception.

Reading a file in reverse order

The reversed() function can be used to read the file line by line or in chunks, in reverse order. This can be applied to both text and binary files.

with open('example.bin', 'rb') as file:
    content = file.read()
    for chunk in reversed(content):
      print(chunk)

Conclusion

Reading files is a crucial aspect of Python programming. By understanding the different file types, methods for reading, access modes, and steps involved, we can efficiently handle files in various programming tasks.

Techniques like reading and writing to the same file, opening files in different modes, and handling file exceptions are essential for practical programming applications.

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