pandas assign with new column name as string
You can pass the keyword arguments to assign as a dictionary, like so:
kwargs = {"ln(A)" : lambda x: np.log(x.A)}df.assign(**kwargs) A B ln(A)0 1 0.500033 0.0000001 2 -0.392229 0.6931472 3 0.385512 1.0986123 4 -0.029816 1.3862944 5 -2.386748 1.6094385 6 -1.828487 1.7917596 7 0.096117 1.9459107 8 -2.867469 2.0794428 9 -0.731787 2.1972259 10 -0.686110 2.302585
assign expects a bunch of key word arguments. It will, in turn, assign columns with the names of the key words. That's handy, but you can't pass an expression as the key word. This is spelled out by @EdChum in the comments with this link
use insert instead for inplace transformation
df.insert(2, 'ln(A)', np.log(df.A))df
use concat if you don't want inplace
pd.concat([df, np.log(df.A).rename('log(A)')], axis=1)