I used to perform operations such as df.query("a > 10") and they work fine.
However, I noticed that when I tried df.query("(a + b) / 2 > 10"), it failed.
Fortunately, when I tried df.eval("(a + b) / 2 > 10"), it works fine.
This leads me to the question what makes eval different from query and when should we use one vs the other?
The df.query is to get the selected rows (where condition is fulfilled) and df.eval is to get boolean output for each row.
e.g.
df123 = pd.DataFrame({'A': range(1, 6),
'B': range(10, 0, -2),
'C C': range(10, 5, -1)})
print(df123)
A B C C 0 1 10 10 1 2 8 9 2 3 6 8 3 4 4 7 4 5 2 6
df123.query('A > B')
A B C C 4 5 2 6
df123.eval('A > B')
0 False 1 False 2 False 3 False 4 True dtype: bool
Hope this helps!