Fast I/O for Competitive Programming in Python

Last Updated : 03 Nov, 2020

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() 