examples/pitfalls/compare_equal.py
x = 2
y = "2"

print(x == y)

with open(__file__) as fh:
    print(fh == x)

In both Python 2 and Pyhton 3 these return False

examples/pitfalls/compare_input.py
import sys

hidden = 42   # would be random

if sys.version_info.major < 3:
    guess = raw_input('Your guess: ')
else: 
    guess = input('Your guess: ')

if hidden == guess:
    print("Match!")

Will never match. Even if user types in 42. - Hard to debug and understand as there is no error.