Python 3 Read from Standard Input (stdin) Like C or Java

I will be using Python3 to read from standard input (or console). I will present two ways of doing this.

First Example

Input (data.txt)

First line of input will contain an integer which tells how many of lines (of data) will follow up. In each of the following lines, there will be one integer and and one floating-point (decimal) number, separated by a space:

3
1 2.3
3 4
5 6.0

Code (iotest.py)

if __name__ == '__main__':
    # Reading the first line and converting it to an integer
    num_entries = int(input())

    # Running a for loop to read each of the following lines
    for i in range(num_entries):
        current_line = input()
        # Getting the two values separated by space in variables `a` and `b`
        a, b = current_line.split()
        a, b = int(a), float(b)
        print(a, b)

Run the program

python3 iotest.py < data.txt

Second Example

Input (data.txt)

In this example, data file exactly looks like the one from first example, except that the first line is missing. Which means, we do not know how many data to read. We would have to run a while loop to read lines till there is and EoF (End of File) which tells us there is nothing more to read.

1 2.3
3 4
5 6.0

Code (iotest2.py)

if __name__ == '__main__':
    try:
        # Running a while loop since we don't know how many lines to read.
        while True:
            current_line = input()
            # Getting the two values separated by space in variables `a` and `b`
            a, b = current_line.split()
            a, b = int(a), float(b)
            print(a, b)
    except EOFError:
        # There is nothing more to do when we reach End of File (EOF)
        pass

Run

python3 iotest2.py < data.txt

Concluding Notes

  • You can run the programs without saving input data in a file. Just type python3 iotest.py and then enter data.
  • Be sure to use Python 3 only as the code will not work in Python 2
  • We are using input() built-in method of Python 3 which reads a single line and returns it as a string. So we have to convert them to appropriate data type (int/float).
Advertisements