Ternary operator example

If you come to Python from a C (or related language as C++ and Java) experience, you have probably developed a taste for the ternary conditional operator (?:). However, Guido van Rossum didn't like it, and it wasn't part of the original language. Luckily for us, in the end he changed his mind, and since version 2.5 it is available a new construct that we can happily use to get this effect. See PEP 308 - Conditional Expressions for details. It goes in this way:

first if test else second

And it reads: check test, if it is true returns first, otherwise second. I found it sort of perlish, but I guess in a while I should get used to it. I reckoned it was sort of fun showing how to use it by a simple programming problem. Say that you have a file containing a bunch of integers, each one on a different line, do not worry about any error handling. You have to write a python script that read that file and output for each number in input a 0 for any odd number and 1 for the even ones. Here is how I solved it:

import sys

data = open(sys.argv[1], 'r')
for line in data:
    print(1 if int(line) % 2 == 0 else 0)

As comparison, In C++ I would have written the same piece of code like this:

int value;
while(file >> value)
    std::cout << (value % 2 == 0 ? 1 : 0) << std::endl;

Fibonacci for CodeEval

Just to have some fun, I was solving a not too complex problem on CodeEval. The description was sort of dodgy, but in the end I understood that it boiled down to calculate the Fibonacci number of the values passed as input (increased by one, to make the waters a bit muddier). I usually play those games in C++, that is my preferred programming language. Alas, on CodeEval we are forced to use a 32 bit C++98 compiler. Not exactly what you could call a state of the art tool. This is particularly annoying in this case, where I need to calculate huge numbers as the Fibonacci ones are. Luckily my basic knowledge of Python is enough to get me out of it. Here is my 2.7 solution, I know it is nothing special, but it sufficed to get me a shiny 100%:

import sys


def fib(n):
    if n == 0:
       return 0

    prev, cur = 0, 1
    for i in range(n - 1):
        prev, cur = cur, prev + cur
    return cur


if __name__ == '__main__':
    for line in open(sys.argv[1]):
        if len(line) > 0:
            print fib(int(line) + 1)