Python iterate over stdin line by line using input()

Python iterate over stdin line by line using input()

To iterate over standard input (stdin) line by line using the input() function in Python, you can use a while loop or a for loop. Here's how you can do it:

Using a while loop:

while True: try: line = input() if not line: break # Exit loop when an empty line is encountered # Process the line print("Read:", line) except EOFError: break # Exit loop when EOF is reached

Using a for loop and iter() function:

import sys for line in iter(sys.stdin.readline, ''): line = line.rstrip('\n') # Remove newline character # Process the line print("Read:", line)

In both examples, the input() function or sys.stdin.readline() is used to read input from stdin. The while loop continues until an empty line or EOF is encountered, while the for loop iterates over lines until an empty line or EOF is reached.

In the for loop example, the iter() function is used to create an iterator that reads lines from stdin until an empty line or EOF is encountered. The rstrip('\n') method is used to remove the newline character from each line.

Remember that when you're running these scripts, you can input lines manually, and the scripts will process each line until you provide an empty line or the end of the input is reached (often signaled by pressing Ctrl+D on Linux/Unix or Ctrl+Z on Windows).

Examples

  1. How to iterate over stdin line by line in Python using input()?

    • Description: To iterate over standard input (stdin) line by line, you can use a loop with input(). This approach is helpful for processing lines from a user or from piped input.
    • Code:
      import sys print("Enter lines of text (CTRL+D to stop):") for line in sys.stdin: # Reads stdin line by line print(f"Line: {line.strip()}")

  2. How to exit a loop reading from stdin with a sentinel value?

    • Description: To exit a loop reading from stdin, you can use a sentinel value or specific input to break the loop.
    • Code:
      print("Enter lines of text (type 'quit' to exit):") while True: line = input() if line == 'quit': # Exit condition break print(f"Received: {line}")

  3. How to read a limited number of lines from stdin in Python?

    • Description: You can read a limited number of lines from stdin by controlling the iteration with a counter or range-based loop.
    • Code:
      print("Enter 3 lines of text:") for _ in range(3): # Limit to 3 lines line = input() print(f"Line: {line.strip()}")

  4. How to handle empty input lines when reading from stdin in Python?

    • Description: When reading from stdin, you might encounter empty lines. You can skip them or handle them as needed during iteration.
    • Code:
      print("Enter lines of text (CTRL+D to stop):") while True: try: line = input().strip() # Remove leading/trailing whitespace if line == "": # Skip empty lines continue print(f"Valid line: {line}") except EOFError: # End of input break

  5. How to read from stdin in Python and save input to a list?

    • Description: To read from stdin and save the input to a list, you can append each line to a list during iteration.
    • Code:
      input_lines = [] print("Enter lines of text (CTRL+D to stop):") try: while True: line = input().strip() if line: input_lines.append(line) # Save to list except EOFError: pass print("Saved lines:", input_lines)

  6. How to read from stdin and convert input to specific data types in Python?

    • Description: When reading from stdin, you might need to convert the input to specific data types (like integers). You can use type casting and error handling to ensure safe conversion.
    • Code:
      print("Enter numbers (CTRL+D to stop):") numbers = [] try: while True: line = input().strip() if line: try: number = int(line) # Convert to integer numbers.append(number) except ValueError: # Handle conversion error print("Invalid number") except EOFError: pass print("Collected numbers:", numbers)

  7. How to process stdin input to separate key-value pairs in Python?

    • Description: If you're reading key-value pairs from stdin, you can split each line by a delimiter to extract keys and values.
    • Code:
      print("Enter key-value pairs (CTRL+D to stop):") kv_pairs = {} try: while True: line = input().strip() if line: key, value = line.split(':') # Split by colon kv_pairs[key.strip()] = value.strip() # Save to dictionary except EOFError: pass print("Collected key-value pairs:", kv_pairs)

  8. How to read lines from stdin and write to a file in Python?

    • Description: To read lines from stdin and write them to a file, you can open a file in write mode and write each input line to the file.
    • Code:
      filename = "output.txt" with open(filename, 'w') as f: print(f"Enter lines of text to save to {filename} (CTRL+D to stop):") try: while True: line = input() if line: f.write(line + '\n') # Write to file except EOFError: pass print(f"Data saved to {filename}")

  9. How to iterate over stdin with a timeout in Python?

    • Description: To iterate over stdin with a timeout, you can use libraries like select to add a timeout condition during input reading.
    • Code:
      import sys import select print("Enter lines of text (timeout after 5 seconds of inactivity):") while True: if select.select([sys.stdin], [], [], 5)[0]: # Timeout after 5 seconds line = input().strip() if line: print(f"Received: {line}") else: print("Timeout reached, no more input.") break

  10. How to handle Ctrl+C or KeyboardInterrupt while iterating over stdin in Python?

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