There is no magic bullet that leads to the fastest input and output in a programming contest. Having said this, there are typically multiple ways of performing and processing input and output in Python3. By understanding the options that are available and how to optimize them (e.g., conducting tests) you can see a real world performance increase, in particular when faced with high volumes of reads and writes.

Input in Python3 is handled via the input() function, and reads a newline-terminated string from standard input.¹⁾ Additional processing is done to the resulting string.

>>> x = input()
Hello World! # x="Hello World!"

>>> x = int(input())
42 # x=42

>>> x = input().split()
Hello World! # x=["Hello", "World!"]

>>> (x, y) = map(int, input().split())
1 2 # x=1, y=2

map() applies a function across a sequence or iterable structure. The comma , unpacks the map object into x and y.

>>> x = list(map(float, input().split()))
1.2 2.3 3.4 4.5 # x=[1.2, 2.3, 3.4, 4.5]

Output is handled with the print() function.

>>> print() # '\n'

>>> print("Hello World!") # "Hello World!\n"

>>> print("Hello", "World!") # "Hello World!\n"

>>> print(1, 2, 3, sep='') # "123\n"

>>> print(1, 2, 3, end='-')
>>> print("a b c") # "1 2 3-a b c\n"

Like the interpreted semantics of Python3, input() and print() are slow compared to their C++ and Java counterparts. The sys library provides faster counterparts.

<code python>

<code python>

10 characters per line (n= number of lines):

1000 characters per line (n= number of lines):

The readline() version is actually slower on the largest dataset. It is attempting to store about 1GB in memory here, causing a slowdown, but still faster than input().

input.py

num_lines = int(input())
 
for i in range(num_lines):
    line = input()

readline.py

from sys import stdin
 
num_lines = int(input())
 
for i in range(num_lines):
    line = stdin.readline()

readlines.py

from sys import stdin
 
num_lines = int(input())
 
lines = stdin.readlines()

read_test.py

from sys import argv
from random import *
from string import *
 
for i in range(int(argv[1])):
    print(''.join(choice(ascii_lowercase + ' ') for _ in range(int(argv[2]))))

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