How do I do multiple things inside one lambda function?

Question

I am learning Python and I want to do multiple things inside one lambda function.

Just for a small example if I want to do addition, subtraction, and multiplication in one function, how do I do that?

I tried to use code like this just to see if it would work and it didn't:

a = 1
b = 2
myFunction = lambda a, b: a + b, b - a, a * b
print(myFunction(a, b))

Don't use a lambda if you are going to give it a name anyway — DeepSpace, Jul 10 '21 at 16:59
did u check https://stackoverflow.com/questions/14843777/how-to-write-python-lambda-with-multiple-lines — Epsi95, Jul 10 '21 at 17:02
Sidenote: [named lambdas are bad practice](/q/38381556/4518341). Use a `def` instead. — wjandrea, Jul 10 '21 at 17:41

mozway · Answer 1 · 2021-07-10T17:13:08.590

2

You can group those operations in a tuple

a = 1
b = 2
myFunction = lambda a, b: (a + b, b - a, a * b)
myFunction(a, b)

output:

(3, 1, 2)

NB. The mistake in you code is that myFunction was a tuple containing your lambda as first element, not a function.

edited Jul 10 '21 at 17:13

answered Jul 10 '21 at 17:00

mozway

score 0 · Accepted Answer · answered Jul 10 '21 at 17:01

0

I think there is a slight syntax issue around a lambda returning a tuple.

Use this syntax:

a = 1
b = 2
myFunction = lambda a, b: (a + b, b - a, a * b)
print(myFunction(a, b))

answered Jul 10 '21 at 17:01

quamrana

1

There is no syntax issue with `lambda` (or at all), it just makes `myFunction` a tuple (just like it would in any other case) – DeepSpace Jul 10 '21 at 17:03
The parenthesis are needed here because Python has no idea if the intention is `lambda a, b: a + b, b - a, a * b`, `lambda a, b: (a + b, b - a), a * b` or `lambda a, b: (a + b, b - a, a * b)` – DeepSpace Jul 10 '21 at 17:06
@DeepSpace: Ok, so what is the name of the issue that requires the programmer to use parentheses to indicate that the lambda should return a `tuple`? – quamrana Jul 10 '21 at 17:06
@DeepSpace is right, the issue is with the grouping. When you do `myfunction = lambda x:x, x`, this creates a tuple that contains the function in the first item and x as the second element. Thus myfunction is a tuple containing a function, not a function. – mozway Jul 10 '21 at 17:12
@mozway: Yes, Is there a reason for that interpretation? Does it have a name? – quamrana Jul 10 '21 at 17:14
2

@quamrana: this is called [operator precedence](https://docs.python.org/3/reference/expressions.html#operator-precedence) – mozway Jul 10 '21 at 17:56

2 Answers2