Some easy tasks solved

Easy tasks solved for Coding Horror

import doctest
 
def reverse(string):
"""
Reverses a string.
 
>>> reverse("hello")
'olleh'
>>> reverse("panda")
'adnap'
"""
result = []
start = len(string) - 1
for index in range(start,-1,-1):
result.append(string[index])
return ''.join(result)
 
def gen_fibs(limit):
"""
Generates the first 'limit' fibonacci numbers.
>>> list(gen_fibs(10))
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34]
"""
a,b = 0,1
for _ in range(limit):
yield a
a,b = b,a+b
 
def get_fib(n):
"""
Returns the 'n'th fibonacci numbers.
 
>>> get_fib(0)
0
>>> get_fib(4)
2
"""
if n == 0: return 0
return list(gen_fibs(n))[-1]
 
def multiplication_tables(limit):
"""
Returns the multiplication tables up to 'limit'.
>>> multiplication_tables(2)
[[1, 1, 1], [1, 2, 2], [2, 1, 2], [2, 2, 4]]
"""
return [[i,j,i*j] for i in range(1,limit+1)
for j in range(1,limit+1)]
 
def sum_from_file(filename):
"""
Returns the sum of all the integers in a textfile,
one integer per line.
"""
with open(filename) as f:
return sum([int(i) for i in f.splitlines()])
 
def odd_numbers(limit):
"""
Returns all the odd numbers up to 'limit'.
 
>>> odd_numbers(10)
[1, 3, 5, 7, 9]
"""
return [i for i in range(1,limit+1) if i % 2 != 0]
 
def largest(array):
"""
Returns the largest value of the array.
 
>>> largest([3,5,7,8,2,1])
8
>>> largest([5,2,10,12])
12
"""
largest_so_far = array[0]
for i in array:
if i > largest_so_far:
largest_so_far = i
return largest_so_far
 
def to_hex(n):
"""
Converts the given number to hexadecimal.
 
>>> to_hex(20)
'14'
>>> to_hex(50)
'32'
"""
digit_symbol_dict = {
10 : "A",
11 : "B",
12 : "C",
13 : "D",
14 : "E",
15 : "F"
}
result = []
while n:
digit = n % 16
digit = str(digit) if digit <= 9 \
else digit_symbol_dict[digit]
result.append(digit)
n //= 16
return reverse(''.join(result))
def format_rgb(triplet):
"""
Converts and rgb triplet to hexadecimal.
>>> format_rgb((100,122,255))
'647AFF'
"""
return ''.join([to_hex(i) for i in triplet])
 
def _test():
doctest.testmod()
 
if __name__ == "__main__":
_test()