<｜begin▁of▁sentence｜>### Instruction:
Given a set of pairs where the first element is the key and the second element is the value, how do you organize these pairs into a dictionary where each key is associated with a list of values, provide functionality to access, modify, and remove those lists of values, and how do you count the number of keys in this dictionary?
### Response:
from collections import defaultdict

# Creating a multidict using defaultdict
multidict = defaultdict(list)

# Adding items to multidict
multidict['spam'].append('eggs')
multidict['spam'].append('bacon')
multidict['spam'].append('ham')

# Accessing items
print(multidict['spam'])  # Output: ['eggs', 'bacon', 'ham']

# Setting a new item, which replaces the old list
multidict['spam'] = ['lobster']
print(multidict['spam'])  # Output: ['lobster']

# Getting the list of all values associated with 'spam'
print(multidict.get('spam'))  # Output: ['lobster']

# Iterating over the multidict
counter = 0
for key in multidict:
    counter += 1
print(f'There are {counter} keys in the multidict.')

# Removing an item
del multidict['spam']
# Now 'spam' should no longer exist in the dictionary
print('spam' in multidict)  # Output: False
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