Fast I/O for Competitive Programming in Python

In Competitive Programming, it is important to read input as fast as possible to save valuable time. Input/Output in Python can be sometimes time taking in cases when the input is huge or to output any numbers of lines or a huge number of arrays(lists) line after line.

Fast Input

Normally, the input is taken from STDIN in the form of String using input(). And this STDIN is provided in the Judge’s file. So try reading the input directly from the Judge’s file using the Operating system(os) module, and input/output (io) module. This reading can be done in the form of bytes. By using this method, integer input works normally, but for string input, it will store the string as a byte like an object. For correcting this, the string can be decoded using the decode function.

Below is the implementation for Fast I/O in Python:

Python3

# Python program to illustrate the use
# of fast Input / Output
import io, os, time

# Function to take normal input
def normal_io():

      # Stores the start time
    start = time.perf_counter()

    # Take Input
    s = input().strip();

      # Stores the end time
    end = time.perf_counter()

    # Print the time taken
    print("\nTime taken in Normal I / O:", \
                      end - start)

# Function for Fast Input
def fast_io():

    # Reinitialize the Input function
    # to take input from the Byte Like
    # objects
    input = io.BytesIO(os.read(0, \
         os.fstat(0).st_size)).readline

    # Fast Input / Output
    start = time.perf_counter()

    # Taking input as string
    s = input().decode()

      # Stores the end time
    end = time.perf_counter()

    # Print the time taken
    print("\nTime taken in Fast I / O:", \
                      end - start)

# Driver Code
if __name__ == "__main__":

    # Function Call
    normal_io()

    fast_io()

Output:

Fast Output

Instead of outputting to the STDOUT, we can try writing to the Judge’s system file. The code for that would be to use sys.stdout.write() instead of print() in Python. But remember we can only output strings using this, so convert the output to a string using str() or map().

Below is the implementation for the Fast Output:

Python3

# Python program to illustrate the use
# of fast Input / Output
import time, sys

# Function to take normal input
def normal_out():

      # Stores the start time
    start = time.perf_counter()

    # Output Integer
    n = 5
    print(n)

    # Output String
    s = "GeeksforGeeks"
    print(s)

    # Output List
    arr = [1, 2, 3, 4]
    print(*arr)

      # Stores the end time
    end = time.perf_counter()

    # Print the time taken
    print("\nTime taken in Normal Output:", \
                      end - start)

# Function for Fast Output
def fast_out():

    start = time.perf_counter()
    # Output Integer
    n = 5
    sys.stdout.write(str(n)+"\n")

    # Output String
    s = "GeeksforGeeks\n"
    sys.stdout.write(s)

    # Output Array
    arr = [1, 2, 3, 4]
    sys.stdout.write(
        " ".join(map(str, arr)) + "\n"
    )

    # Stores the end time
    end = time.perf_counter()

    # Print the time taken
    print("\nTime taken in Fast Output:", \
                      end - start)

# Driver Code
if __name__ == "__main__":

    # Function Call
    normal_out()

    fast_out()

Output: