<s>[INST] import pandas as pd
df = pd.DataFrame({'A': [1, 2, 3, 4, 5], 'B': [6, 7, 8, 9, 10]})
df['C'] = df['A'] * df['B']
print(df)

# Output:
#    A   B   C
# 0  1   6   6
# 1  2   7  14
# 2  3   8  24
# 3  4   9  36
# 4  5  10  50

# Later in the code...
df.drop(columns=['A'], inplace=True)
print(df)
# Output:
#    B   C
# 0   6   6
# 1   7  14
# 2   8  24
# 3   9  36
# 4  10  50

# Now we want to recalculate column C by multiplying A and B.
df['C'] = df['A'] * df['B']

# Traceback (most recent call last):
#  File "<stdin>", line 1, in <module>
# KeyError: 'A'

# What's the issue here?[/INST]