When working with dictionaries in Python, it is common to encounter situations where we need to assign multiple values to a single key. This can be particularly useful when dealing with data from Excel spreadsheets, as it allows us to store and access multiple values associated with a specific key.

Option 1: Using a List as the Value

One way to solve this problem is by using a list as the value for each key in the dictionary. We can then append new values to the list whenever needed.

excel_data = {
    'key1': [],
    'key2': [],
    'key3': []
}

# Read data from Excel and assign values to keys
for row in excel_rows:
    key = row['key']
    value = row['value']
    excel_data[key].append(value)

In this example, we initialize an empty list as the value for each key in the dictionary. Then, for each row in the Excel data, we retrieve the key and value and append the value to the corresponding list in the dictionary.

Option 2: Using a Dictionary as the Value

Another approach is to use a nested dictionary as the value for each key. This allows us to store multiple values associated with different attributes of the key.

excel_data = {
    'key1': {'value1': [], 'value2': []},
    'key2': {'value1': [], 'value2': []},
    'key3': {'value1': [], 'value2': []}
}

# Read data from Excel and assign values to keys
for row in excel_rows:
    key = row['key']
    value1 = row['value1']
    value2 = row['value2']
    excel_data[key]['value1'].append(value1)
    excel_data[key]['value2'].append(value2)

In this example, we create a nested dictionary where each key has multiple attributes (e.g., ‘value1’, ‘value2’). For each row in the Excel data, we retrieve the key and values and append them to the corresponding attributes in the nested dictionary.

Option 3: Using the defaultdict Class

The third option involves using the defaultdict class from the collections module. This class automatically initializes the values for new keys, allowing us to directly append values without explicitly initializing them.

from collections import defaultdict

excel_data = defaultdict(list)

# Read data from Excel and assign values to keys
for row in excel_rows:
    key = row['key']
    value = row['value']
    excel_data[key].append(value)

In this example, we create a defaultdict with the list class as the default factory. This means that whenever a new key is accessed, it will automatically be initialized as an empty list. We can then directly append values to the list without explicitly initializing it.

After considering these three options, the best choice depends on the specific requirements of your project. If you only need to store and access multiple values for each key, option 1 using a list as the value is a simple and efficient solution. However, if you need to associate multiple attributes with each key, option 2 using a nested dictionary provides more flexibility. Finally, if you prefer a more concise syntax and automatic initialization of values, option 3 using the defaultdict class is a convenient choice.