conditionals in lambda statements

Question

I'm trying to find duplicates in a list by using a lambda function:

f = lambda z,y: z=[] if z[0]==y[0] and z[1]==y[1]

I have a list like

[['hey','ho'], ['hey','ho'], ['howdy','no']]

and I would like

['hey','ho'], ['howdy','no']]

I get the error:

>>> f = lambda z,y: z=[] if z[0]==y[0] and z[1]==y[1] else z=z
  File "<stdin>", line 1
SyntaxError: can't assign to lambda

Don't understand the downvotes, just trying to ask why python disagrees with the assignment — Falcata, Jun 05 '15 at 21:11
This is the solution without lambda: http://stackoverflow.com/questions/2213923/python-removing-duplicates-from-a-list-of-lists — fsacer, Jun 05 '15 at 21:17
@Falcata Downvotes reflect a perceived lack of research, given that you could have answered the question by looking up the correct syntax for both lambda expressions and conditional expressions. — chepner, Jun 05 '15 at 21:50

score 3 · Answer 1 · answered Jun 05 '15 at 21:20

The lambda needs to be an expression that evaluates to some value. It should not be an assignment to a variable. Get rid of the assignments to z.

f = lambda z,y: [] if z[0]==y[0] and z[1]==y[1] else z

or more simply

f = lambda z,y: [] if z==y else z

(Strange variable names, by the way. Why z and y, and why are they backwards?)

1 Answers1