Use pd.concat instead because df.append is deprecated

[thomasjpfan]

pd.concat is deprecated in pandas 1.X and was removed in 2.0. XREF: pandas-dev/pandas#35407

pd.concat does not error if the columns do not match. It results in nan values:

import pandas as pd

df1 = pd.DataFrame(data={"col1": [10, 2], "col2": [10, 4]})
df2 = pd.DataFrame(data={"col3": [5, 10], "col4": [5, 10]})

print(pd.concat([df1, df2]).to_markdown())

	col1	col2	col3	col4
0	10	10	nan	nan
1	2	4	nan	nan
0	nan	nan	5	5
1	nan	nan	10	10