Find the element in a list that has the most consecutive repetitions

Longest Repetition in a List

# Question 8: Longest Repetition

# Define a procedure, longest_repetition, that takes as input a 
# list, and returns the element in the list that has the most 
# consecutive repetitions. If there are multiple elements that 
# have the same number of longest repetitions, the result should 
# be the one that appears first. If the input list is empty, 
# it should return None.

def longest_repetition(input_list):
    if len(input_list) == 0:
        return None
    u_elements = unique_elements(input_list)
    counter_list = []
    for element in u_elements:
        i = 0
        freq, in_a_row = 1, 1
        while i < len(input_list) - 1:
            if element == input_list[i] and input_list[i] == input_list[i+1]:
                freq = freq + 1
                in_a_row = freq
            else:
                freq = 1
            i = i + 1
        counter_list.append([element, in_a_row])
    return get_first_highest(counter_list)

# Finds the unique elements of a list
def unique_elements(input_list):
    unique_elements = [input_list[0]]
    for element in input_list:
        if element not in unique_elements:
            unique_elements.append(element)
    return unique_elements

# Returns the most frequent element in 'counter' list in form [[element,frequency],...]; if multiple, returns the first, "maximum" frequency element. 
def get_first_highest(counter_list):
    last_highest_freq = 0
    for key_value_pair in counter_list:
        if key_value_pair[1] > last_highest_freq:
            last_highest_freq = key_value_pair[1]
            highest_freq_element = key_value_pair[0]
    return highest_freq_element
   
#For example,

print longest_repetition([1, 2, 2, 3, 3, 3, 2, 2, 1])
# 3

print longest_repetition(['a', 'b', 'b', 'b', 'c', 'd', 'd', 'd'])
# b

print longest_repetition([1,2,3,4,5])
# 1

print longest_repetition([])
# None