This code won't output anything:

def print$\_$solution$($houses$)$:

for i$,$ house in enumerate$($houses$)$:

print$($f$"$House $\{$i $+1\}$:$")$

print$($f$"-$ Nationality: $\{$house$[\text{'}$nationality$\text{'}]\}")$

print$($f$"-$ Color: $\{$house$[\text{'}$color$\text{'}]\}")$

print$($f$"-$ Drink: $\{$house$[\text{'}$drink$\text{'}]\}")$

print$($f$"-$ Smoke: $\{$house$[\text{'}$smoke$\text{'}]\}")$

print$($f$"-$ Pet: $\{$house$[\text{'}$pet$\text{'}]\}$

$")$

def solve$\_$houses$()$:

houses $=[\{\text{'}$nationality$\text{'}$: 'Norwegian', 'color': 'yellow', 'drink': 'milk', 'smoke': 'Dunhills', 'pet': 'walleye pike'$\},$

$\{\text{'}$nationality$\text{'}$: 'Brit', 'color': 'red', 'drink': 'tea', 'smoke': 'Blends', 'pet': 'birds'$\},$

$\{\text{'}$nationality$\text{'}$: 'Swede', 'color': 'blue', 'drink': 'coffee', 'smoke': 'Pall Malls', 'pet': 'dogs'$\},$

$\{\text{'}$nationality$\text{'}$: 'Dane', 'color': 'white', 'drink': 'tea', 'smoke': 'Princes', 'pet': 'cats'$\},$

$\{\text{'}$nationality$\text{'}$: 'German', 'color': 'green', 'drink': 'beer', 'smoke': 'Bluemasters', 'pet': 'horses'$\}]$

def print$\_$solution$($houses$)$:

for i$,$ house in enumerate$($houses$)$:

print$($f$"$House $\{$i $+1\}$:$")$

print$($f$"-$ Nationality: $\{$house$[\text{'}$nationality$\text{'}]\}")$

print$($f$"-$ Color: $\{$house$[\text{'}$color$\text{'}]\}")$

print$($f$"-$ Drink: $\{$house$[\text{'}$drink$\text{'}]\}")$

print$($f$"-$ Smoke: $\{$house$[\text{'}$smoke$\text{'}]\}")$

print$($f$"-$ Pet: $\{$house$[\text{'}$pet$\text{'}]\}$

$")$

def backtrack$($house$\_$index$)$:

if house$\_$index $==$ len$($houses$)$:

return True

for house in houses:

if house$\_$index $==0$:

house$[\text{'}$color$\text{'}]=$ 'yellow'

elif house$\_$index $==1$:

house$[\text{'}$color$\text{'}]=$ 'blue'

elif house$\_$index $==2$:

house$[\text{'}$color$\text{'}]=$ 'red'

elif house$\_$index $==3$:

house$[\text{'}$color$\text{'}]=$ 'green'

elif house$\_$index $==4$:

house$[\text{'}$color$\text{'}]=$ 'white'

if house$\_$index $==0$:

house$[\text{'}$nationality$\text{'}]=$ 'Norwegian'

elif house$\_$index $==1$:

house$[\text{'}$nationality$\text{'}]=$ 'Dane'

elif house$\_$index $==2$:

house$[\text{'}$nationality$\text{'}]=$ 'Brit'

elif house$\_$index $==3$:

house$[\text{'}$nationality$\text{'}]=$ 'German'

elif house$\_$index $==4$:

house$[\text{'}$nationality$\text{'}]=$ 'Swede'

if house$\_$index $==0$:

house$[\text{'}$drink$\text{'}]=$ 'water'

elif house$\_$index $==1$:

house$[\text{'}$drink$\text{'}]=$ 'tea'

elif house$\_$index $==2$:

house$[\text{'}$drink$\text{'}]=$ 'milk'

elif house$\_$index $==3$:

house$[\text{'}$drink$\text{'}]=$ 'coffee'

elif house$\_$index $==4$:

house$[\text{'}$drink$\text{'}]=$ 'beer'

if house$\_$index $==0$:

house$[\text{'}$smoke$\text{'}]=$ 'Dunhills'

elif house$\_$index $==1$:

house$[\text{'}$smoke$\text{'}]=$ 'Blends'

elif house$\_$index $==2$:

house$[\text{'}$smoke$\text{'}]=$ 'Pall Malls'

elif house$\_$index $==3$:

house$[\text{'}$smoke$\text{'}]=$ 'Princes'

elif house$\_$index $==4$:

house$[\text{'}$smoke$\text{'}]=$ 'Bluemasters'

if house$\_$index $==0$:

house$[\text{'}$pet$\text{'}]=$ 'cat'

elif house$\_$index $==1$:

house$[\text{'}$pet$\text{'}]=$ 'horses'

elif house$\_$index $==2$:

house$[\text{'}$pet$\text{'}]=$ 'birds'

elif house$\_$index $==3$:

house$[\text{'}$pet$\text{'}]=$ 'fish'

elif house$\_$index $==4$:

house$[\text{'}$pet$\text{'}]=$ 'dogs'

if check$\_$constraints$($house$\_$index$)$:

if backtrack$($house$\_$index $+1)$:

return True

reset$\_$house$($house$\_$index$)$

return False

def check$\_$constraints$($house$\_$index$)$:

if house$\_$index $==0$:

return houses$[1][\text{'}$nationality$\text{'}]==$ 'Norwegian' and houses$[1][\text{'}$color$\text{'}]==$ 'yellow' and houses$[1][\text{'}$drink$\text{'}]==$ 'water' and houses$[1][\text{'}$smoke$\text{'}]==$ 'Dunhills' and houses$[1][\text{'}$pet$\text{'}]==$ 'cats'

elif house$\_$index $==1$:

return houses$[0][\text{'}$nationality$\text{'}]==$ 'Dane' and houses$[0][\text{'}$color$\text{'}]==$ 'blue' and houses$[0][\text{'}$drink$\text{'}]==$ 'tea' and houses$[0][\text{'}$smoke$\text{'}]==$ 'Blends' and houses$[0][\text{'}$pet$\text{'}]==$ 'horses'

elif house$\_$index $==2$:

return houses$[2][\text{'}$nationality$\text{'}]==$ 'Brit' and houses$[2][\text{'}$color$\text{'}]==$ 'red' and houses$[2][\text{'}$drink$\text{'}]==$ 'milk' and houses$[2][\text{'}$smoke$\text{'}]==$ 'Pall Malls' and houses$[2][\text{'}$pet$\text{'}]==$ 'birds'

elif house$\_$index $==3$:

return houses$[3][\text{'}$nationality$\text{'}]==$ 'German' and houses$[3][\text{'}$color$\text{'}]==$ 'green' and houses$[3][\text{'}$drink$\text{'}]==$ 'coffee' and houses$[3][\text{'}$smoke$\text{'}]==$ 'Princes' and houses$[3][\text{'}$pet$\text{'}]==$ 'fish'

elif house$\_$index $==4$:

return houses$[4][\text{'}$nationality$\text{'}]==$ 'Swede' and houses$[4][\text{'}$color$\text{'}]==$ 'white' and houses$[4][\text{'}$drink$\text{'}]==$ 'beer' and houses$[4][\text{'}$smoke$\text{'}]==$ 'Blue Masters' and houses$[4][\text{'}$pet$\text{'}]==$ 'dogs'

def reset$\_$house$($house$)$:

initial$\_$house $=\{\text{'}$nationality$\text{'}$: 'Norwegian', 'color': 'yellow', 'drink': 'milk', 'smoke': 'Dunhills', 'pet': 'walleye pike'$\}$

for key, value in initial$\_$house.items$()$:

house$[$key$]=$ value

if $\_\_$name$\_\_=="\_\_$main$\_\_"$:

houses $=[\{\text{'}$nationality$\text{'}$: 'Norwegian', 'color': 'yellow', 'drink': 'milk', 'smoke': 'Dunhills', 'pet': 'walleye pike'$\},$

$\{\text{'}$nationality$\text{'}$: 'Brit', 'color': 'red', 'drink': 'tea', $\text{'}$