[Python] How to concatenate n rows of content, to current row, in a rolling window, in pandas?

I'm looking to transform a dataframe containing

[[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]

into [[1, 2, 3, []], [4, 5, 6, [1, 2, 3, 4, 5, 6]], [7, 8, 9, [4, 5, 6, 7, 8, 9]], [10, 11, 12, [7, 8, 9, 10, 11, 12]]]

So far the only working solution I've come up with is:

import pandas as pd
import numpy as np

# Create the DataFrame
df = pd.DataFrame(np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9], [10, 11, 12]]))

# Initialize an empty list to store the result
result = []

# Iterate over the rows in the DataFrame
for i in range(len(df)):
# If it's the first row, append the row with an empty list
if i == 0:
result.append(list(df.iloc) + [[]])
# If it's not the first row, concatenate the current and previous row
else:
current_row = list(df.iloc)
previous_row = list(df.iloc[i-1])
concatenated_row = current_row + [previous_row + current_row]
result.append(concatenated_row)

# Print the result
print(result)


Is there no build in Pandas function that can roll a window, and add the results to current row, like the above can?

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