python - Using local variables with multiple assignments with pandas eval function

Question

The pandas help file says (for eval): As a convenience, multiple assignments can be performed by using a multi-line string.

However, I'm finding that doesn't work with variables (using ipython):

This works:

df_price.eval("op = op * @mult", inplace = True)

But this does NOT work (op, cl, hi, lo are cols in dataframe df_price where mult is a float):

df_price.eval("""op = op * @mult
              cl = cl * @mult
              hi = hi * @mult
              lo = lo * @mult""", inplace = True)

error: pandas.computation.ops.UndefinedVariableError: local variable 'mult' is not defined

Answer 1

I can confirm that the local variables appear to only work on the first line of a multi line eval expression. A possible work around:

df_price.eval("""mult = @mult
              op = op * mult
              cl = cl * mult
              hi = hi * mult
              lo = lo * mult""", inplace = True)

This does however have the side effect of creating an extra column.

Update:

I have submitted a Pull Request with a fix for this issue.