Python Input and Output

Practical Examples

Simple Text Editor

def simple_text_editor():
    """A very simple text editor."""
    filename = input("Enter filename to edit: ")
    
    # Try to load existing file
    try:
        with open(filename, "r") as file:
            content = file.read()
        print(f"Loaded file: {filename}")
    except FileNotFoundError:
        content = ""
        print(f"New file: {filename}")
    
    # Show current content
    print("\nCurrent content:")
    print("-" * 40)
    print(content)
    print("-" * 40)
    
    # Edit content
    print("\nEnter new content (type 'EOF' on a new line to finish):")
    new_content = []
    while True:
        line = input()
        if line == "EOF":
            break
        new_content.append(line)
    
    # Save or discard changes
    save = input("\nSave changes? (y/n): ").lower()
    if save == "y":
        with open(filename, "w") as file:
            file.write("\n".join(new_content))
        print(f"Changes saved to {filename}")
    else:
        print("Changes discarded")

# Uncomment to run the editor
# simple_text_editor()

CSV Data Processor

import csv

def process_csv_data(input_file, output_file):
    """Read CSV data, process it, and write results to a new CSV file."""
    
    # Read input data
    with open(input_file, "r", newline="") as infile:
        reader = csv.DictReader(infile)
        data = list(reader)
    
    print(f"Read {len(data)} rows from {input_file}")
    
    # Process data (simple example: calculate age in months)
    for row in data:
        try:
            age_years = int(row["Age"])
            row["Age_Months"] = age_years * 12
        except (ValueError, KeyError):
            row["Age_Months"] = "N/A"
    
    # Write output data
    with open(output_file, "w", newline="") as outfile:
        # Get all field names, including new ones
        fieldnames = list(data[0].keys())
        writer = csv.DictWriter(outfile, fieldnames=fieldnames)
        
        writer.writeheader()
        writer.writerows(data)
    
    print(f"Processed data written to {output_file}")

# Example usage
# process_csv_data("people.csv", "people_processed.csv")

Log File Analyzer

def analyze_log_file(log_file):
    """A simple log file analyzer that counts error types."""
    error_types = {}
    
    try:
        with open(log_file, "r") as file:
            line_count = 0
            error_count = 0
            
            for line in file:
                line_count += 1
                
                # Simple example: count lines containing "ERROR"
                if "ERROR" in line:
                    error_count += 1
                    
                    # Extract error type (simple example)
                    parts = line.split("ERROR:", 1)
                    if len(parts) > 1:
                        error_message = parts[1].strip()
                        # Get first few words as error type
                        error_type = " ".join(error_message.split()[:3])
                        
                        error_types[error_type] = error_types.get(error_type, 0) + 1
        
        # Print summary
        print(f"Log File Analysis: {log_file}")
        print(f"Total lines: {line_count}")
        print(f"Error lines: {error_count} ({error_count/line_count:.1%} of total)")
        
        if error_types:
            print("\nError Types:")
            for error_type, count in sorted(error_types.items(), key=lambda x: x[1], reverse=True):
                print(f"- {error_type}: {count} occurrences")
    
    except FileNotFoundError:
        print(f"Error: Log file '{log_file}' not found.")
    except Exception as e:
        print(f"Error analyzing log file: {e}")

# Example usage (create a sample log file first)
with open("sample.log", "w") as log:
    log.write("2025-04-15 12:30:45 INFO: Application started\n")
    log.write("2025-04-15 12:31:10 ERROR: Database connection failed\n")
    log.write("2025-04-15 12:31:15 INFO: Retrying connection\n")
    log.write("2025-04-15 12:32:20 ERROR: Database connection failed\n")
    log.write("2025-04-15 12:33:45 ERROR: Invalid user input\n")
    log.write("2025-04-15 12:35:12 INFO: User logged in\n")

# analyze_log_file("sample.log")