Notes on File Handling in Python

Introduction to File Handling

• File Handling: Allows reading from and writing to disk files in Python. It enables data storage beyond program execution.

Data Files

• Text Files:
  • Store data as ASCII or Unicode characters.
  • Example: "computer" takes 8 bytes, 11237.9876 takes 10 bytes.
  • End-of-Line (EOL) characters: '\n' or '\r'.
• Binary Files:
  • Store data in its raw memory format (e.g., integers, floats).
  • No EOL delimiters.
  • Faster and more efficient but requires specific reading through Python.

Steps in Data File Handling

1. Opening Files:
   • Syntax: file_object = open(filename, mode)
   • Default mode: 'r' (read). Other modes include 'w' (write), 'a' (append).
2. Performing Read/Write Operations:
   • Read:
     • file_object.read([n]): Reads n bytes or the entire file if n is omitted.
     • file_object.readline([n]): Reads a line or n bytes.
     • file_object.readlines(): Reads all lines into a list.
   • Write:
     • file_object.write(str): Writes string str to the file.
     • file_object.writelines(list): Writes a list of strings to the file.
3. Closing Files:
   • Syntax: file_object.close()
   • Ensures data is saved and file resources are released.

File Modes and Paths

• Opening File Modes:
  • 'r': Read (default).
  • 'w': Write (overwrites file).
  • 'a': Append (adds to the end).
• File Path Syntax:
  • Absolute Path: Full path from the root, e.g., C:\SALES\2018\REVENUE.TXT.
  • Relative Path: Relative to the current directory, e.g., .\2019\SHEET.XLS.
  • Double Backslash (\): Used in paths to escape the backslash, e.g., d:\\mydata\\poem.txt.
  • Raw Strings: Use r before the string to treat backslashes literally, e.g., r"d:\mydata\poem.txt".

File Operations

• File Handle: The reference to the file used for reading/writing operations.
• Flush: file_object.flush() forces the buffer to write to the file.
• Stripping Whitespace: Use .strip(), .lstrip(), or .rstrip() to remove whitespace from strings.

Standard Input, Output, and Error

• Standard Input (stdin): Reads from the keyboard.
• Standard Output (stdout): Writes to the monitor.
• Standard Error (stderr): Writes errors to the monitor.
  • Using sys module:pythonCopy codeimport sys sys.stdin, sys.stdout, sys.stderr

Using with Statement

• Context Manager:
  • Syntax: with open(filename, mode) as file_handle: # file operations
  • Automatically closes the file after the block of code.

Binary File Operations

• Pickle Module:
  • Dump: pickle.dump(object, file_handle) writes an object to a binary file.
  • Load: pickle.load(file_handle) reads an object from a binary file.

Current Working Directory

• Getting Current Directory:
  • import os pwd = os.getcwd() print("Current Directory:", pwd)