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How to Handle Multi-Line User Input in Python

Collecting multi-line user input is a common requirement in interactive Python applications. Whether you need to gather several lines of text or handle input until a specific signal (like EOF), mastering different input methods is essential.

This guide explores various techniques for handling multi-line user input in Python.

Collecting Multi-Line Input with a Loop​

One approach to handling multi-line input is using a while loop combined with the input() function. You can control the loop based on user input to gather multiple lines.

lines = []

while True:
    user_input = input()

    if user_input == '':
        break
    else:
        lines.append(user_input + '\n')

print(lines)
print(''.join(lines))

Explanation:

  • We initialize an empty list called lines.
  • The while True loop continuously prompts the user for input using input().
  • If the user presses Enter without typing any text, the input will be an empty string (''). In this case, the if statement executes a break to exit the loop.
  • If the user types text, the else statement executes, and we append the input string along with a newline character \n to the lines list, ensuring proper line separation.
  • Finally, the code prints the list of strings, followed by a single string with the multiple lines concatenated together using join.

This approach is flexible and allows you to customize the exit condition based on your needs (e.g., a specific "stop word").

Reading Input Until EOF using sys.stdin.readlines()​

The sys.stdin.readlines() method offers a more direct way to read multi-line input until an End-Of-File (EOF) signal is encountered. The EOF signal is triggered by pressing Ctrl + D (Unix/macOS) or Ctrl + Z (Windows) in the terminal.

import sys

print('Press CTRL + D (Unix) or CTRL + Z (Windows) to exit')
user_input = sys.stdin.readlines()

print(user_input)
print(''.join(user_input))

Explanation:

  • We import the sys module, which provides access to system-specific parameters and functions, including standard input.
  • sys.stdin.readlines() reads all input lines from the terminal until an EOF signal is received and returns a list of strings, where each string represents a line of input.
  • The code prints this list and then joins the elements into a single string for display.
note

This method is ideal for capturing multi-line input from standard input, such as when piping data from another process.

Reading Input Until EOF using sys.stdin.read()​

If you only need the input as one single string containing all the lines, the sys.stdin.read() method is a good fit. This method returns the entire input stream as a string.

import sys

user_input = sys.stdin.read()
print(user_input)

Explanation:

  • sys.stdin.read() reads the entire input stream until an EOF signal is received and returns it as a single string including newline characters.
  • The code prints this single string.
note

This is useful if you don't need the individual lines.

Reading Input Until EOF with Try/Except Blocks​

You can also use a try/except block to handle input until EOF. In this case, the EOFError is captured when the EOF signal is sent.

lines = []

while True:
    try:
        lines.append(input())
    except EOFError:
        lines_str = '\n'.join(lines)
        print(lines_str)
        break
print(lines)

Explanation:

  • We start with an empty lines list.
  • The while True loop continuously attempts to get input using input().
  • When the user sends an EOF signal (Ctrl+D or Ctrl+Z), the input() function raises an EOFError exception.
  • The except EOFError block catches the exception.
  • We join the lines together with newline characters into a single string lines_str, and then print it.
  • The break statement is used to exit the loop.
  • Finally, the code prints the list of the input lines.
note

This approach provides a more explicit way to handle EOF and allows you to perform specific actions before exiting the loop.

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